Environmentally Responsible Gardening Practices

These are practices that have been used here in Chapel Hill, NC, located near latitude 35.93 and longitude 79.04. The Garden is located in USDA Plant Hardiness Zone 7B. Our goal is to grow healthy plants while simultaneously preserving diversity and the overall balance of nature. Where control measures are warranted, we seek to use the minimum approach necessary to manage the problem.

a staff member gardens in the fern display

Please remember that it is imperative to read all of the direction on any product's label and observe all of the precautions recommended by the manufacturer. Even less-toxic products must be handled with care. In some cases brand names are mentioned to help locate an appropriate product.

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Most insects are benign or beneficial in the garden. Many insects, for instance, play an invaluable role in pollination resulting in the production of fruits and viable seeds. Learn more about pollinators and how you can help them at this N.C. Cooperative Extension website.

Students in Garden

Great Spangled Fritillary on Asclepias tuberosa.
(Photo courtesy of Joanna Massey Lelekacs)

Some species are true pests. It is very important to identify an unknown insect as the first step of management, and make sure that it is harmful, rather than immediately using an insecticide. For insects that turn out to be pests, there are a variety of options for treatment. See http://attra.ncat.org/pest.htm for more information.

A few insect species that people think of as beneficial in their gardens are not really so helpful.

Praying mantises are often considered beneficial, but they indiscriminately kill any insects that catch their eye, including valuable pollinators such as honeybees. Most mantis egg cases that are sold are actually Chinese mantises, a non-native species, that have in many areas almost eliminated the native mantises. Similarly, Asian ladybugs were introduced into the United States in hopes of their controlling pests such as aphids. Native ladybugs can no longer be found in many areas due to the Asian ladybugs' predation.

Ants are often beneficial in the garden. They aerate the soil as well as doing an excellent job mixing different kinds of materials throughout the soil.

It is rarely necessary to control ants. If ants move into an area that is unsuitable, such as plant containers, you can flood the pot with water from a hose. This usually will cause them to move elsewhere. If necessary, you can also use boric acid liquid baits that will specifically target ants. These must be kept away from children and pets.

The red imported fire ant can pose more of a threat. This species has moved into our area within the last few years and it can cause serious hazards, since it stings with little provocation. Its stings are very painful, and can cause a life-threatening situation, if an individual receives numerous stings. For least-toxic controls for fire ants, see http://attra.ncat.org/attra-pub/fireant.html for more information.

Caterpillars eat the leaves of a number of plant species, both in the nursery and the landscape. In some cases, no control is needed. Established plants survive partial defoliation well, though they may look ratty for a while. An important part of gardening for wildlife is to provide host plants for larvae. You can identify the species of caterpillar to learn more about its habits by going to http://ipm.ncsu.edu/AG136/caterkey.html

Physically protecting plants is one option, with a lightweight row cover fabric such as Reemay. If you find you need to control caterpillars while you have only a few, they can be hand-picked and dropped into a cup of soapy water. Products containing Bt (Bacillus thuringensis) that specifically target caterpillars can be used for more widespread populations. This bacterium selectively kills only caterpillars, and is only toxic to them after they have eaten it.

Chewing or sucking insects, such as aphids and flea beetles, can occasionally cause problems on a wide variety of plants. Aphids can often be controlled simply by washing them off plants, using a strong stream of water from a hose. Susceptible plants can be protected from flea beetles by covering them with floating row cover fabric. Repellents such as those containing garlic, hot pepper or neem may help.

Fungus gnats can be troublesome in the containers of house plants or in greenhouses. These small pests, resembling fruit flies, lay their eggs on damp soil. Their larvae eat plant roots, especially those of seedlings. Pyrethrin spray is effective for controlling adult fungus gnats. During the springtime, we have used scheduled applications of beneficial nematodes to control the larvae of fungus gnats in NCBG's greenhouse. There are also forms of Bt (Bacillus thurigensis) that are only toxic to the larvae of fungus gnats.

Other Pests

Snails and slugs may eat plants, especially during wet weather. Look for the silvery trails they leave behind that indicate their activity. Sometimes it is possible to improve cultural conditions, such as by removing objects under which snails and slugs can hide. Physical barriers, such as strips of copper or a ring of crushed eggshells, also can help protect the most susceptible plants.

If you have more widespread damage, you may want to use a bait against snails and slugs. Many products on the market contain metaldehyde are also highly toxic to mammals. There are also snail and slug baits available that contain iron phosphate as their active ingredient. These less-toxic products, such as Sluggo and Escar-Go, are not poisonous to birds and small animals. These products have been highly effective in controlling slugs and snails in our nursery and greenhouse.

Deer are likely to eat many ornamental plants. It is a good idea to choose species that are less likely to be grazed. Please be aware that many lists of deer-resistant plant species include plants that are invasive in the southeastern United States. By cross-checking our list of invasive exotic plants you can avoid these troublesome species. Keep in mind, however, that if deer are hungry enough, they have been known to eat almost any plant.

If you can prevent deer from establishing a habit of grazing in your garden, that will help. Repellents may be useful, if you are diligent about applying them as recommended. Some people use three different repellents in rotation in the hope that when applied in this way, they will act as a greater deterrent.

Physical barriers such as chicken wire can be used to block access to new plants. While there is expense and time involved in its installation, in the long run a fence is the best defense against deer. Plan on building a fence that is a minimum of 6 1/2 feet tall. A fence topped with an electrified wire can be particularly effective over time. You can also purchase fence netting that is nearly invisible from a distance. A double barrier, that is, a fence within a fence, works especially well because it is confusing to the deer. Netting that is laid flat on the ground is also an effective deterrent, because deer hate to step on it. You can find more information about repelling and excluding deer from your landscape at http://www.attra.org/attra-pub/deercontrol.html

Moles and voles have some similarities but are very different creatures. Moles have a characteristic large snout. They dig tunnels beneath the surface of the soil. They aerate the soil and eat insects, grubs, and earthworms rather than plants so overall they can be considered beneficial. You may want to press down areas in your turf where the soil surface has been disrupted.

Voles are smaller than moles, about the size of a mouse. They sometimes dig tunnels, and also have been known to travel about in the tunnels that were previously dug by moles. Meadow voles are a different species that lives above ground. Voles eat plant parts including roots and bulbs, and can be very destructive to ornamental plants.

Some have found it helpful to mix sharp-edged pea gravel throughout the soil as they prepare to put in new plants. Products called Perma-Till (www.permatill.com) and VoleBloc (www.volebloc.com) are also useful deterrents when used in this way.

Rabbits can cause damage to plants. They are particularly drawn to the tender new growth of some species. Repellents such as those containing hot pepper can be helpful in deterring their grazing, if you are conscientious about applying them according to the label directions. Physical barriers can be used to block access, such as chicken wire.

Plant Diseases

Powdery mildew is caused by a fungus characterized by gray patches on the foliage. Many species are prone to this disease in our climate. Powdery mildew can be unattractive, but often does not pose a hazard to the plant's health. For severe cases, baking soda has been used against powdery mildew and other fungi. Visit the National Sustainable Agriculture Information Service website for more information on using baking soda as a fungicide.

For plants growing from a basal rosette of foliage, such as columbine (Aquilegia canadensis) the affected leaves can be cut back and removed, if powdery mildew becomes troublesome.

There are numerous species of leaf-spot funguses can cause dark blotches on foliage. In some cases, the dead tissue drops away, leaving a hole in the leaf. These are called shothole fungi. Conventional fungicides often contain some of the most dangerous chemicals on the market. Even organic fungicides such as Bordeaux mix contain sulfur and can be very toxic to humans, pets, and other organisms. There are other fungicidal products available that contain less hazardous substances.

In our climate, the temperature range and humidity levels are suitable for many fungi to reproduce for a period of many months: from April through November. Fungicides must be applied every 7 to 10 days over this time period to remain effective. Considering the cost of the fungicides, and the time spent applying them, as well as their limited effectiveness overall, you may choose to remove the susceptible plants and find more substitutes.

Alternatively, in some instances you may find it is sufficient to make cultural changes, such as improving the air circulation in the plant's area. Applying a quick-drying mulch beneath the plant such as a layer of pea gravel or sand may help, too.

Weeds and Invasive Plants

Weeds are often defined simply as plants that are growing in the wrong place. Most weeds are annual or biennial herbaceous plants. Weeds may be either native or exotic in origin. While they can be troublesome or unsightly within an area, they are not a threat to the balance of nature by reducing desirable species overall.

Invasive plants are also plants that are out of place. Many, though not all, are woody species. Most invasive plants are shrubs, trees, vines, or aquatic plants. These plants outcompete more desirable species. Generally they are not subject to the diseases or insect pests that kept them in check in the areas where they originated. Unlike weeds, invasive species reduce species diversity and cause degradation of natural areas.

Most invasive species initially were grown as ornamental plants. Many produce fruits and seeds that are eaten by birds, who then disseminate the seed widely. Some species, such as bamboo grass (Microstegium vimineum) were first introduced to this area by accident.

In many areas, a combination of timely applications of mulch and regular spot weeding controls weeds very effectively. Preventing weeds from maturing and producing seeds is the key to weed management. If you keep weeds from going to seed in your yard, that saves you time and effort in the years to come. Perhaps there is bamboo grass (Microstegium vimineum) growing on the property of your neighbor who lives uphill from you, that has the potential to disperse seed onto your land, too. Ideally, you can network with your neighbors on controlling plants that can adversely affect all of you.

Recognizing new weeds as they begin to appear in your garden will help control them in a timely way. Most weed seedlings can be identified by the time their second set of leaves have appeared. You may notice a weed that was previously unknown to you that germinates from seed brought in with new plants, topsoil, or mulch.

A topical application of corn gluten, spread before weed seeds begin to germinate, is an organic way to inhibit seed germination. These products such as WOW from Gardens Alive (www.gardensalive.com) are produced as a byproduct of corn wet-milling. Corn gluten is effective in retarding germination in an area for approximately six weeks. It degrades into a form of nitrogen that acts as a fertilizer and is not harmful to people or pets. Corn gluten should not be applied where the germination of desirable seeds is anticipated within the next six weeks.

Hand-held flame and infrared heat weeders that burn propane gas are useful for killing weeds without the use herbicides. Organic farmers have found these to be very useful. In order to be most effective and use your time well, it is important to choose an appropriately sized tool for the task at hand. Flame weeders (www.flameengineering.com/Weed_Dragon.html) are particularly useful for killing weeds in open areas, not close to desirable plants. Infrared heat weeders cost more than flame weeders but are more useful for working in close quarters. Another alternative, the steam weeder, we have not tried at the North Carolina Botanical Garden, but it is becoming more widely available for sale to home gardeners.

Tools such as the Weed-Wrench (www.weedwrench.com) are very useful for physically pulling larger woody plants, root and all. There are four different sizes of Weed-Wrench that work well for various sizes of invasive exotic woody plants. Another lighter-weight tool called the Root Talon (www.invasive.org/gist/tools/rtalon.html) is designed for killing shallow-rooted undesirable plants.

Herbicides kill plants via a variety of mechanisms. Careful timing is important in order for these products to work most effectively. Some herbicides are soap-based, such as the brand Scythe. The product BurnOut is in another group of less-toxic herbicides that are made with lemon juice and fermented vinegar. Another option is AllDown by Summerset (www.alldownherbicide.com) that is approved for certified organic growers. These products work particularly well in controlling annual weeds that do not have an extensive root system.

RoundUp and similar herbicides with the active ingredient glyphosate can be used to control perennial weeds and invasive plants. These nonselective systemic herbicides can be sprayed on the foliage of weeds, or a concentrated form is painted on the freshly cut stems of woody plants. They work best on perennial weeds that are actively growing and not stressed by drought or other factors. The cut-and-paint method works best in late summer and fall, when the plant is concentrating energy reserves in its roots.

The long-term effects of herbicides on human health and the environment are unknown. RoundUp herbicide contains a surfactant that helps the spray stick better to whatever it contacts. Some tests have indicated that the surfactant in RoundUp may pose more hazards than glyphosate.

Physical barriers can be used to eradicate aggressive plants. We have used cardboard in conjunction with a thick layer of mulch to smother English ivy and other aggressive groundcovers. This is an excellent control for large areas without the use of herbicides. It works most effectively during the cooler months of the year. To be most effective, the ivy should be first be sheared back close to ground level by using a string trimmer. Then lay down a couple of sheets of corrugated cardboard, such as flattened boxes. Spread three inches of leaf or bark mulch on top to create a thick barrier. You will need to be attentive and keep clipped to ground level any branches of ivy that grow up through the mulch for the next few years. This method is much more successful, and is much less labor-intensive, than trying to pull all the ivy by hand.

Additional Resources


General Info


Integrated Pest Management (IPM)

Questions about gardening?
Visit our Green Gardener Clinic! A garden curator, trained volunteer, or Orange County Master Gardener is available every weekday from noon to 2 pm at the Green Gardener Desk in the Education Center (central building). You may also call (919-962-0522) at that time with your gardening/plant questions.

Published on March 06, 2013 at 11:26:22 am.

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