Organic Horticulture in the Mid-Atlantic/Printable version

Organic Horticulture in the Mid-Atlantic

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Weed Management

Weed Management

Weed control is at the core of gardening, since without it the garden would eventually revert to meadow, scrubland, and eventually forest. As with most garden chores, prevention and diligence are key, since weedy plants tend to grow much faster than ornamentals and crops.

Long-term control requires three steps when engaging in weed control: knowing the weeds, removing the weeds, and preventing the re-emergence of the weeds.

1. Know the Weeds

Like cultivated plants, each species of weed has its unique optimal growth conditions, habit, and life cycle, so being able to identify the weeds is essential for achieving effective control. Some weeds are easily controlled within a season, while others may require a longer-term commitment, but knowing how a weed spreads and reproduces enables the gardener to come up with a management plan for each type.

For professional gardeners, learning the common weeds found in the region is both easier and more useful than knowing the cultivated plants, since most gardens will only have perhaps 20 species of weed, while on the other hand having many more species and cultivars of desired plants. Knowing which plants should always be removed -- and knowing the best way to remove and dispose of them -- makes it much easier to simply jump into a garden and clean it up, rather than needing a "tour" of each new site to see what the "good plants" are.

Annual vs. Perennial

The simplest distinction that needs to be made is whether a weed is an annual (growing from seeds each year), or perennial (growing from persistent roots or woody parts). Annual weeds can in most cases be controlled with greater ease, since one needs only interrupt the reproductive cycle, while perennials need to be controlled at the root as well as breaking the reproductive cycle.

Perennial weeds tend to have more substantive root systems, and most will grow back if at least the vast majority of the root is not removed or otherwise destroyed. Serious infestations of rhizomatous or stoloniferous plants (such as canada thistle, mugwort, nutsedge, or bindweed) may require soil barriers to smother the plants over a season.

Annual weeds, on the other hand, tend to be much easier to pull, but also produce very large amounts of seed, since they do not use any energy on building up reserves of starches to survive winters (or summers, in the case of winter annuals).

Biennial weeds are somewhere in between, since they spend their first year building up starches, and then use up all these starches at the end of their life cycles to produce seeds.

The second most important thing to know is when the seeds are produced and how they are spread. Removing weeds after they have gone to seed does nothing to prevent further germination (which can be an even greater problem when herbicides are used, since even after the weed appears to be "dead", the seeds can in many cases continue to develop). Grubbing before flowers are produced is the best time. If flowers are already present, the weeds should be treated as if seeds were present when deciding on a disposal method.

Roots

Knowing the type of root that a weed has, how firmly it is attached to the above ground parts, as well as how much of the root is needed for the plant to re-grow is important for proper, long-term control. Weeds with taproots or woody roots require digging tools for removal, while plants with shallow or noncomplex root systems can often simply be pulled by hand. See the chapter on weeding tools.

How weeds spread

All weeds spread by seed, and some perennials also spread vegetatively (through roots, stolons, etc.). How seeds are transported from the parent plant to the garden is important to understand, particularly since some weeds are easily spread on feet or on tools.

Weeds that spread vegetatively are often the most intractable, since stoloniferous and rhizomatous weeds often grow back from even the smallest root fragments. Such weeds can best be controlled by soil barriers (such as newspaper and mulch), by removing and replacing the soil outright, or when those methods are simply not an option (for example, when perennial weeds are growing among desirable plants that cannot be transplanted away), control can be achieved after a time by diligent and regular grubbing.

Weeds that spread by seed can often be managed with a preventative approach. The most effective preventative is simply ensuring that the soil is always covered by a layer of seed-free mulch, since this will prevent any seeds on the soil surface from being exposed to light, which is the signal that causes many seeds to germinate. For this same reason, any time the soil is disturbed (by grubbing weeds, planting, or any other reason), fresh mulch should be added to cover up the disturbed area, since weed seeds will have been brought to the surface.

Weeds can also be controlled using Corn Gluten Meal (CGM), which is a byproduct of corn processing. While this only works for smaller seeds, it is an excellent choice for lawns and other areas (such as vegetable gardens) where mulches can't be used. CGM breaks down into nitrogen and other fertilizers after 4-6 weeks, after which it must be re-applied.

Seed dispersal methods vary from plant to plant. Many plants rely on birds or other animals to disperse the seeds. Others are spread by wind. Finally, many are spread by foot traffic, tools, lawn mowers, etc.

Birds spread seeds by eating the fruits, then passing the seeds a short while later. Bird-spread weeds are thus most common around the edges of shrubs, under power lines or other places where the bird perches. Little can be done to prevent birds from spreading these seeds, so the soil underneath regular perching spots should simply be kept well-mulched or otherwise shaded (by dense ground covers, etc.) to prevent germination, and regularly patrolled for seedlings (particularly tree seedlings) that are able to germinate despite preventative measures.

Nut-producing trees generally rely on squirrels and other rodents to plant the seeds deep in the soil. Neither mulch nor CGM provides any control to these plants, since their germination is triggered by soil temperature and moisture. Discouraging squirrels or removing any nearby nut-producing trees are the only preventatives. Weeds of this group need to be pulled as soon as they are seen, since most of them quickly develop deep taproots that make larger plants very difficult to remove.

Wind-spread seeds end to settle against windbreaks or in low areas. The germination of smaller seeds can be prevented by either CGM or diligent mulching. Larger seeds (such as maple, ash, tuliptree, etc.) should be blown off after they fall, before additional mulch is laid down.

Finally, weed seeds are also found in the soil itself, lying dormant under the surface (these seeds are known as the "soil seed bank"). This is why it is important to always add fresh mulch after weeds are removed, because once these dormant seeds are exposed to sunlight, they will germinate almost immediately.

Many of the most common weeds of the region produce very small seeds that are dispersed on feet, tools, and other equipment. While these weeds are among the most numerous found in the field, their numbers can be drastically reduced by proper hygiene in the garden. When pulling these weeds, hey should be immediately put into a container (never left on the lawn, soil, or even on hard surfaces), tools should be wiped down after working near them or in soil where they are present, and shoes should be wiped or hosed off when moving from a weedy area to an area already cleaned.

With all weeds, a key management strategy is to prevent seeds from being produced whenever possible. For example, nearby waste areas, unkempt woodlands, or invaded wildflower meadows should be monitored for problem weeds, and where possible mown or cleared before the seeds ripen. In many cases it is certainly worthwhile to eradicate seed sources even on neighboring properties (even just mowing or trimming weeds before the seeds ripen).

2. Preparation and the waste stream

Once the weeds found on a site have been identified, the next step is to have the right tools ready, prepare for dealing with the waste stream, and finally make sure the site is ready to be worked on.

Tools include a hand cultivator to loosen soil around the roots, a hoe for larger areas that have only seedlings, a tote to put the weeds in (or two totes, if using "split-stream" disposal), pruners for tree seedlings that are too well-established to pull out effectively, and finally a pair of gloves for removing spiny, thorny, or poisonous plants.

For disposal a compost area should be kept ready to accept materials. If using "hot" composting, all materials can go to the same place. If a cold compost system is being used on-site, seed-bearing materials must be kept separate in order to prevent further dispersal when the compost is used in the garden.

To prepare the site, make sure the edges are well-defined, if possible make sure the lawn was recently mown, and (again, if possible) the soil should me moist but not wet to make roots easier to remove.

Finally, a supply of mulch should be on-hand to cover any areas of soil that are disturbed during the process.

3. Removing the weeds and preventing re-emergence

Once the weeds are identified and the tools and site are prepared, it's time to start grubbing them out. Different weed species require different removal methods, but the control method will also depend on where they are growing, the density of the desired plantings, etc.

In large, open areas where there are not currently any desirable plants, hoeing (particularly with stirrup hoes or offset hoes) is often the most efficient way to get the weeds out. If some plants are unable to be hoed, follow up with a mattock-type cultivator or if necessary with a spade for deeply tap-rooted plants. When hoeing, always follow up immediately by raking off the area, and then adding a layer of mulch.

In areas that are more densely planted, use the claw part of a mattock-type cultivator to loosen the soil below the weed by hitting just behind it and prying gently. This allows the root system to be removed intact, and is especially important for weeds that spread by rhizomes or are easily broken away from the root system when pulling. Mulch areas where the soil has been loosened immediately in order to prevent any newly-exposed soil seeds from germinating.

If the soil is soft and moist enough, simply manually pulling is often the easiest way. When pulling by hand, use a slow, firm motion rather than trying to jerk the weeds out, since this will more often than not cause the top of the weed to simply break off of the root. If gloves are worn, make sure the gloves fit very tightly so that the gardener can grab the plant just beneath the soil surface at the crown, rather than trying to pull by the above-ground stems. Again, add mulch to prevent new weeds from germinating.

If weeds are growing within the crowns of desirable plants, first try simply pulling, making sure to grab just below the soil line and also making sure that the weed (not the garden plant) is what's being pulled.

In more extreme cases (such as when lawn grass or other grasses get into a perennial forb), it may be necessary to dig up the plant, separate out the weed roots (bare-rooting may be necessary), and replant. Bear in mind that the perennial will be stressed in the process, and may need shelter from direct sunlight for a few days, and may need extra irrigation for several weeks if this is done in summer. Alternatively, simply snip the weeds at the soil line and return regularly, putting off digging until fall when the plant will not be as badly stressed.

In all cases, remember to put the weeds directly into a container for disposal, since putting the weeds on soil, lawn, or other surfaces will give the plant an opportunity to drop its seeds as it dries out, and risks leaving perennial root fragments behind that may regrow under the new mulch.

See also:

For more about weed control, see:

• Composting methods
• Quarantine
• Soil barriers

Pinkweeds

Persicaria spp. (Pinkweeds, Lady's Thumb)

Pinkweeds, otherwise known as smartweeds or lady's thumbs are any of a number of plants in the genus Persicaria (formerly Polygonum), including both native and invasive species. The weedy species are all annual plants with simple, smooth-margined leaves, and often have a dark marking (a "lady's thumbprint") in the center of each leaf. The leaves and branches are alternate, with each node somewhat swollen and covered by a thin sheath (the old genus name "Polygonum" roughly means "many-knees"). Pinkweeds have a fibrous root system and may root at the nodes where the stems touch the ground. Grubbing out is generally easy, and cultivators may be used on young plants. With the exception of the young seedlings, plants should be composted only in hot systems, since the plants can continue to grow and/or set seed in cold piles. Some species of Persicaria are grown as garden plants as well, though these species tend to look quite different from the weedy types.

Along a garden edge P. maculosa, showing root Closeup of stem node

Common ragweed

Ambrosia artemisiifolia (Common Ragweed)

Ambrosia artemisiifolia (Common Ragweed) is an annual native plant which emerges from any exposed soil in mid-spring. Leaves are opposite and finely dissected. The root consists of a thick white taproot, developing axillary hairs as the season goes on. The plants are easily grubbed, and can be composted safely until flowers are produced in summer (the small yellow flowers are held on terminal green spikes). Young plants can sometimes be mistaken for seedlings of garden plants such as Acer japonicum. Seeds are produced in early autumn, and are spread by foot traffic and wind.

Flowering plant young plant Plant with roots

Chenopodium album

Chenopodium album (Lamb's quarters)

Lamb's Quarters (Chenopodium album) is an annual invasive weed most commonly found in dry, nitrogen-rich soils. The alternate, somewhat "kite-shaped" leaves have a dusty appearance. Stems are stout, longitudinally ridged, and also whitish. Roots consist of large taproots with numerous laterals. Pulling and grubbing is relatively easy, since the root and shoot are strongly connected. This plant is safe to compost in cold piles before the flowers appear in summer. Flowers are greenish terminal spikes. While rarely seen in Mid-atlantic gardens, the culinary grain Quinoa (C. quinoa) is almost indistinguishable from the weed species, so maintenance crews should always be advised if that species is being grown in the garden. Epazote, or Wormseed (Dysphania ambrosioides) is somewhat similar when in flower, but the foliage is markedly different from Lamb's Quarters.

young plant flowerbuds flowers

Bidens frondosa

Bidens frondosa (Devil's Beggarticks)

Bidens frondosa (devil's beggarticks) is an annual native plant found naturally in low meadows but also a common weed of gardens. The plants emerge in mid spring, flowering in mid to late summer, then producing seeds that stick to clothing. Despite being an annual, the plant can produce very tough root systems. Cold-pile composting is safe before flowers are produced. Plant

Flower seeds

Oxalis

Oxalis (Woodbines)

The genus Oxalis (Woodbines) contains both native and invasive weedy species that are common throughout the region. Two species are erect annuals, while the third is a creeping perennial. All species have trifoliate leaves with heart-shaped leaflets. On the annual types the leaves are a pale green, while on the perennial creeping species the leaves are purplish. Flowers are small, yellow, and trumpet-shaped with 5 lobes. Horn-like seed pods soon follow, opening explosively when ripe. When pulling oxalis, plants should always be put directly into a container (not piled) to avoid broadcasting the seeds. With the exception of very small seedlings, they should never be composted in a cold pile. The creeping species (O. corniculatus) will regrow from small root fragments, so care must be taken to get the entire root. It can be distinguished from the other species by the purplish cast to the foliage and a lower growing habit rooting at the nodes.

O. stricta Creeping woodsorrel, O. corniculatus flower

Grasses

Weedy Grasses

Weedy grasses are a large group of plants that pop up in nearly every garden. These grasses include escaped lawn grasses, seedlings of ornamental grasses, and any number of native and invasive grasses that get into the garden. The trick with weedy grasses lies in being able to identify them in contrast to desirable plants which may have grass-like leaves.

Illustration Crabgrass Young plant

Wild Onions

The weedy species of wild onions in the Mid-Atlantic are generally one of two species: the invasive Allium arvense or the native Allium canadensis. For horticultural purposes, they are both treated in the same way as weeds, though A. arvense tends to form larger clumps and is more likely to become a weed of lawns.

Both plants need to be grubbed using a weeding tool that can get the roots out, since the roots tend to be deep and the stems easily break away allowing the plant to regrow. Both species will grow back from either the main bulb or the bulblets, so the area should be inspected for weed regrowth a week or two after the initial grubbing.

Pokeweed

Phytolacca americana (Pokeweed)

Phytolacca americana (pokeweed) is a shrub-like native herbaceous perennial with green or reddish stems, large leaves, and a long, fleshy taproot. The plant's seeds are berries that are spread by birds, and frequently are found around the driplines of trees, shrubs, and along fencerows. Pokeweed can be difficult to pull due to the very heavy and deep taproots, and a full-sized mattock may be required for large specimens. Seed supplies can be reduced by at least cutting down plants in adjacent uncultivated areas before the berries ripen. Seeds may germinate under mulch, and paper barriers are ineffective as the plant can push through. Pokeweed shoots can be composted in cold piles if berries are not present (roots should not be added to cold piles).

Flowers Root

Chinese Bittersweet

Chinese Bittersweet (Celastrus orbiculatus) is an invasive vine spread by birds which eat the fruits in fall and winter. The vine climbs by twining, and can grow quite rapidly over garden plants or other structures.

The vines have a shallow root system and are thus easily pulled. Larger vines on trees and shrubs need to be cut off the tree rather than pulled off to avoid breaking branches.

Rudbeckia triloba

Rudbeckia triloba, the Brown-eyed Susan, is a native wildflower in the Mid-Atlantic, but can also become quite weedy in the garden or field. It is a short-lived perennial, producing flowers in summer and fall. Germination occurs any time during the growing season.

Plants are usually best controlled by pulling. Prevent reseeding by removing spent flowers.

The plant is sometimes cultivated, so consult the garden planner before eradicating. Spent flowers are sometimes left on the plant to attract birds such as the goldfinch or house finch.

Cold-pile composting is safe if flowers or seeds are not present.

Cyperus esculentus

Cyperus esculentus (Yellow Nutsedge)

Cyperus esculentus (yellow nutsedge) is a perennial, grass-like plant that is a common perennial weed of gardens and lawns. The leaves are shiny and yellowish, with spiny flowers appearing in late summer. The plant spreads aggressively by underground stolons, and in late summer also produces small starchy tubers. The plant can grow back from very small root fragments, so the soil should be loosened with a claw-type cultivator when pulling, and diligence is required for several months to attain full control Wet or compacted soils favor the growth of this plant, so improving soil structure and drainage is the most effective long-term control. Plant

Flowering plant in a lawn (the yellow patch) Plant with roots

Euphorbia maculata

Euphorbia maculata (Creeping Spurge) Euphorbia maculata (creeping spurge) is a mat-forming native annual weed common throughout the region. It grows on any exposed soils, in sunny or partially shaded locations. The leaves are opposite, usually with a purple center on the upper side, on reddish stems. The tiny white flowers are quickly followed by very small seeds which are easily moved on shoes, tools, etc. Remove by pulling, or by hoeing followed by mulch. Plants should not be disposed of in cold composting systems, since they produce copious seed. The stems of this plant contain a milky sap that can cause skin irritation in susceptible people.

Flowering plant with roots closeup of flowers Young plant

Grasses

Weedy Grasses

Weedy grasses are a large group of plants that pop up in nearly every garden. These grasses include escaped lawn grasses, seedlings of ornamental grasses, and any number of native and invasive grasses that get into the garden. The trick with weedy grasses lies in being able to identify them in contrast to desirable plants which may have grass-like leaves.

Illustration Crabgrass Young plant

Poison ivy

Toxicodendron radicans (Poison Ivy) Toxicodendron radicans (poison ivy) is a deciduous woody vine or shrub common throughout the Mid-Atlantic, and is one of the most problematic weeds because the oils it contains causes severe rashes in most people. The plant can be difficult to identify because the leaflets have a great variation in shape, but they are always trifoliate, alternate on the stem, and usually have a reddish petiole. The bark is a warm gray color to cinnammon reddish brown. Mature vines exhibit hair like rootlets resemble rusty steel wool when climbing. Like English ivy and many other climbing vines, the mature form has branches that grow perpendicular to the main vine produce small yellowish white flowers and greenish looking fruits. Flowers are yellowish green in early summer, while the white/grey drupes (seeds) mature in autumn, often persist through winter. All parts of the plant contain the oil urushiol, which is the chemical responsible for causing an allergic reaction (Urushiol-induced contact dermatitis). The toxin is present all year, and persists in dormant branches and dead fallen leaves. The prolific plant seeds are spread by wind, small rodents, and birds. The drupes serve as an important persistent food source. Once spring arrives seedlings will be found growing anywhere birds, mammals congregate, particularly where they perch or hide, such as on fences, shrubs, and small trees. Removal Removal of poison ivy requires special care, especially by susceptible individuals. Slightest skin contact can be neutralized by "washing" the skin immediately with soil to bind the urushiol (urushi oil), and there are a number of soaps available to remove the oils as well. Tools exposed to the plant, especially its sap, should not be reused or handled without thorough cleansing. While the hazard of the urushiol makes it difficult to work with this plant, its root systems tends to be shallow and relatively easy to remove. The roots contain the highest urushiol concentrations When removing from trees, the vine can simply be cut at the base by removing a 1-2" x - section using pruners, lopers or a straight bladed saw (it is difficult to avoid cutting the tree's bark using a curved saw). When cutting large vines or cutting up trees that are covered in the vine with a chainsaw, always use the top of the cutting blade to throw any sap away from the chainsaw operator. Disposal Disposal of poison ivy must always be approached with utmost care, since the plant material, dead or alive always contains urushiol, and can cause the known rash to occur. It never should be burned, since burning causes the urushiol to vaporize into aerosol, makes it airborne, and can cause severe respiratory problems or even death if inhaled. As it causes your lungs to internally blister next causing you to drown in your own fluids. Vines located on fire wood thoroughly need to be removed prior to burning of wood Poison ivy can be chipped and hot composted, but care should be taken to segregate the chips since they should not be used as uncomposted mulch on pathways.

Illustration foliage with entire margins Young foliage with lobed margins vine on a tree

Epilobium

Euphorbia maculata (Creeping Spurge) Epilobium (willow-herbs) are a group of erect herbaceous plants in the evening primrose family. A few species are native wildflowers, and in the garden commonly present as weeds. The plants pull easily, and can be cold-composted before flowers are produced, or heat composted after flowering.

No images available yet

Clearing multiflora rose

Rosa multiflora (multiflora rose) is a highly invasive plant that colonizes woodlands, roadsides, and open areas. Its presence is in part du to its having been introduced as a "habitat plant" for birds along railroads and highways, and it does in fact provide nesting habitat and winter food for many songbirds. However, over the years it has become a very problematic plant, since it crowds out native understory plants and is quite difficult to remove due to the sharp, recurved thorns.

Aside from the use of herbicides, the plant can be controlled organically using mechanical methods and/or by grazing with goats.

Mechanical removal

While very young stems can be simply cut down my mowing, larger plants require heavier equipment, such as chainsaws, brush saws, and/or tractors. Roots can be removed by digging, or with the use of tractors or stump grinders, or can be left in place if regular mowing is an option.

Mechanical removal using a front loader, forklift tines, and chainsaw

The tops of large plants can be quickly removed using a front-loader with forklift tines, by lifting the crowns and then cutting the exposed trunks underneath. This has the added benefit of making disposal easier.

Disposal of tops

Because of the thorns, chipping is generally not a good option. Tops can instead be piled and compacted for slow composting, or else burned.

In the winter, multiflora rose also makes a good winter fodder for goats (which eat the bark, small stems, and fruits), so it can be piled in the barnyard for this purpose. After the rose dries, it can be disposed of by composting or burning.

Newspaper and mulch weed barriers

One of the most effective ways to control perennial weeds in the organic garden is to use the "newspaper-and-mulch method". The way it works is quite simple: the newspaper acts as a physical barrier which prevents perennial weeds from growing above-ground, which over time starves the plants, since they are unable to photosynthesize. The results are very good if it’s done properly.

This method should not be used around some shallow-rooted shrubs (particularly some plants in Ericaceae). Digging dogs and squirrels can undo the barriers as well, so the treated areas need to be monitored carefully if these animals are present in the garden. The method works very well for some of the worst common weeds in the region, including:

• Cirsium arvense (Canada Thistle)
• Trifolium (Clover)
• Artemisia vulgaris (mugwort)

It can also be used to kill lawns in preparation for adding a bed the following year, or as a base layer for raised beds.

Tools and Materials

• Newspaper or cardboard: A large amount of newspaper of cardboard is needed, since to be effective the barrier beeds to be at least 1 cm (about 1/3 inch) thick when wet. Newspaper can often be attained from local recycling centers, cardboard from supermarkets (call the market first and ask them to save it).
• Plastic or metal bins: Shallow, flat bottomed containers to hold water, large enough to fit a folded newspaper section. This might not be useful when using cardboard, depending on the size of the boxes.
• Covering material: Mulch, compost, soil, or gravel needs to be put on top of the paper to keep it from blowing away (and to hide it from sight).

Site preparation

Once all the materials are together, it’s time to prepare the area for application. If it is a new bed (without ornamental plants already growing), start by mowing or weed-wacking as close to the ground as possible. Tilling is also an option, as long as you can get the soil good and smooth afterwards, and compact it a bit with a rake. Make sure that the outermost 6 inches or so of the bed are as weed-free as possible, so plants can't just grow around the barrier.

If there are already ornamental plants growing, more care is needed. Shrubs and small trees with shallow root systems will not appreciate having paper on their roots, so you’ll need to carefully hand-weed within their driplines. Outside the dripline, cultivate just as you would on a new bed. Perennials are usually OK with the newspaper laid within 4” of their crowns.

If the bed is badly invaded with running weeds like bindweed, thistle, goutweed, it’s usually better to just cut everything down to the ground, transplant and quarantine the shrubs, and apply newspaper to the entire area.

Application

Prepare the newspaper by thoroughly soaking it in water to give it weight and help it bind together. The easiest system for doing this is to have two tubs of water, so one tub can be used for soaking while you pull paper out of the other one.

Once the paper is thoroughly wet, begin laying it down on top of the soil. Use whole sections, not unfolded, and let them overlap by 1/2, so that the entire soil surface has 2 sections on it, at least 1/4 inch thick (1/2 inch is even better). Once the paper is down, pat the sections together so they’ll start to form a continuous layer. This layer will keep perennial weeds or turf from poking through, effectively smothering the weeds and denying them light. Leave at least 2 inches on the outer portion of the bed to allow for edging without having to cut through the paper.

Once the paper is down, and before it starts to dry, start laying down mulch on top. Don’t dump wheelbarrows on the paper, but instead place it by hand, to avoid disturbing the newspaper as much as possible (unlike mulching without a barrier, it's actually better to go from front to back, rather than back to front). Put on enough mulch to thoroughly cover the paper, as this will not only look nicer, but will also prevent the wind from blowing the paper around the yard.

If it’s a “must plant” location, use 6 inches of compost instead of mulch, and grow annuals and shallow rooting vegetables on top (keep in mind that you’ll need to water the bed more often than the surrounding soil, because soil moisture will not wick up through the paper barrier as much as it would if the paper wasn’t there). With that much compost sitting atop the bed, it’s a good idea to use some logs on the edge (on top of the paper) to keep it from washing into adjacent areas.

Maintenance

As a rule, you’ll want to leave the bed alone for about a year to ensure that the perennial weeds are completely smothered. Use the area in the meantime for containers, ornaments, to store new plant acquisitions in, or as the quarantine site for any shrubs you might have moved.

Make a regular inspection for tenacious weeds that might try to pop through the paper, and if you see any, brush the mulch aside, find the hole they’re using, and add a patch layer of newspapers to seal it up.

Once you’ve had a full year without any weeds poking through, it’s safe to till the bed and start growing in it. Keep in mind that there will still be weed seeds in the soil, but the pernicious perennials will be history, as long as you keep on top of the new seedlings. If using a tiller, remove any large pieces of paper and add them to the compost pile, as they are a carbon source and may divert nitrogen from the soil.

Tree rings

In the horticultural sense, a tree ring is an area around the trunk of the tree that is maintained as a barrier between the surrounding lawn and the tree's base to avoid unintentional damage from mowing equipment. This area is generally kept mulched or planted with a ground cover or other ornamental plants. "Tree ring" is also a colloquial term for the annual growth rings found in a tree's wood.

Tree rings provide an important purpose in protecting the tree, since being bumped by mowers or hit by rotary weed trimmers can cause severe damage to the base of the tree by either crushing or removing the cambium layer (thus causing a dead area), or by simply exposing the cambium which makes the tree susceptible to infection or insect damage since the protective bark is removed. Eventually this can cause the parts of the tree above the damaged area to die, or in extreme cases the whole tree can die due to disease or unintentional girdling.

Tree rings should at a minimum be at least 1 foot (30 cm) beyond the flare of the tree's base, though wider is better. If there are surface roots beyond the tree ring that are being hit by mowing equipment, the ring should be expanded to include those roots, since scarfing the roots also created open wounds and thus make the tree susceptible to infection.

While tree rings are often maintained by simply maintaining a layer of mulch, the use of ground covers is a much better option in most cases, since the presence of a ground cover will discourage people from walking on the soil within the ring, and so helping to avoid soil compaction. Dense ground covers such as Pachysandra terminalis, Epimedium, and so on are the best choices, since they require less weeding and so less foot traffic within the ring.

In cases where surface roots continue to appear outside of an existing tree ring, vertical mulching can be used to provide better air, water, and nutrient circulation within the deeper soil, which will encourage the tree to grow deep roots rather than surface roots.

Print version 6.16.08-001

This is a print version for "Organic Horticulture in the Mid-Atlantic", prepared June 16, 2008 by --SB_Johnny | ^PA!

Chenopodium album (Lamb's quarters)

Lamb's Quarters (Chenopodium album) is an annual invasive weed most commonly found in dry, nitrogen-rich soils. The alternate, somewhat "kite-shaped" leaves have a dusty appearance. Stems are stout, longitudinally ridged, and also whitish. Roots consist of large taproots with numerous laterals. Pulling and grubbing is relatively easy, since the root and shoot are strongly connected. This plant is safe to compost in cold piles before the flowers appear in summer. Flowers are greenish terminal spikes. While rarely seen in Mid-atlantic gardens, the culinary grain Quinoa (C. quinoa) is almost indistinguishable from the weed species, so maintenance crews should always be advised if that species is being grown in the garden. Epazote, or Wormseed (Dysphania ambrosioides) is somewhat similar when in flower, but the foliage is markedly different from Lamb's Quarters.

young plant flowerbuds flowers

Oxalis (Woodbines)

The genus Oxalis (Woodbines) contains both native and invasive weedy species that are common throughout the region. Two species are erect annuals, while the third is a creeping perennial. All species have trifoliate leaves with heart-shaped leaflets. On the annual types the leaves are a pale green, while on the perennial creeping species the leaves are purplish. Flowers are small, yellow, and trumpet-shaped with 5 lobes. Horn-like seed pods soon follow, opening explosively when ripe. When pulling oxalis, plants should always be put directly into a container (not piled) to avoid broadcasting the seeds. With the exception of very small seedlings, they should never be composted in a cold pile. The creeping species (O. corniculatus) will regrow from small root fragments, so care must be taken to get the entire root. It can be distinguished from the other species by the purplish cast to the foliage and a lower growing habit rooting at the nodes.

O. stricta Creeping woodsorrel, O. corniculatus flower