Dealing with weeds: the garden’s uninvited guest
By Dawn Pettinelli - UConn Home & Garden Education Center
Featured Article - posted Wed., Jun. 26, 2013
With the growing season underway, most people are delighted as the grass greens up, spring shrubs and trees burst into bloom, and perennials start to poke their heads out of the ground. Not so happy are they to discover a multitude of weeds in their shrub and garden beds, or in their lawns. A weed is defined as a plant in a place that it is not wanted. One person’s weed is often another’s treasure. For instance, I don’t really mind the violets, Robin’s plantain, wild strawberries, and buttercups in the lawn. They remind me of wildflower meadows in Montana, and the blossoms are essential to pollinators, like bees. A weed-free lawn is the equivalent of a food desert to pollinators! That being said, I know numerous land owners deplore non-turf species and want to limit their range.
Many weed problems can be avoided by proper cultural practices. Plants that are healthy and well cared for will have a greater ability to out-compete weed species. It is important to select plants suitable to the site where they will be planted, regardless of whether you are selecting annuals, perennials, trees or shrubs.
Trying to establish a bluegrass lawn in a heavily-shaded area is just begging to be invaded by weeds. Better you should choose a shade-tolerant groundcover or just put some mulch under trees. If one insists on a lawn, then some tree branches will need to be removed to allow more light into the area. No lawn does well with little direct sun, even ones planted with shade-tolerant fescues. They still need a minimum of four hours of direct sunlight each day.
A newly-established garden bed may harbor weed seeds if it was recently rototilled. Usually one will see some weed seeds germinating after it rains or the bed is watered. Use a hoe or other weeding tool to make quick work of these uninvited guests before they go to seed or take over.
Mulches are a great way to reduce weed growth, along with their many other benefits. Organic mulches such as grass clippings (provided the lawn wasn’t treated with herbicides), shredded leaves, pine needles, cocoa hulls and bark mulches not only reduce water loss while helping to control weeds, but they will eventually break down and be incorporated into the soil. This will increase the organic matter content of the soil.
Black plastic mulches were popular in the vegetable garden and were used to raise the soil temperatures for earlier planting of tender vegetables. These have largely been replaced by black landscape fabric which will warm the soil but also let air and water pass through it. I remember a number of people having problems when they used the black plastic around shrubs in foundation plantings. Because it wasn’t permeable, it was difficult to get enough water to the plants’ root systems in dry years, and in wet years, the root systems remained saturated because the water could not easily evaporate.
The best time to apply mulch is right now. After removing any weeds from an area, lay down a 2- to 3-inch layer of organic mulch. Keep the mulch from touching the stems of trees and shrubs and the bases of perennials. Rolls of biodegradable paper mulch might be useful in the vegetable garden. Large staples can be made from metal coat hangers, or purchased, to use to hold the mulch down so it won’t blow away. They are also needed when putting down the black fabric mulches for the same reason.
The old-fashioned but most thorough way to remove weeds is by hand-digging. One distinct advantage of hand-weeding, however, is that it puts the gardener in very close proximity to the garden. Plant growth and development, as well as insect and disease problems, become quite evident when in your face!
Just-emerging weeds can be sliced at ground level, but older ones need to have their root system completely pulled up. Hand-weeding, as most of us know, is quite time- and labor-intensive, not to mention hard on the knees.
Because of this, some people look to chemical controls. To kill plants, one would use an herbicide, which is a chemical that kills weeds. Herbicides are placed in several categories, depending on how they affect plants. They fall into the broad categories of selective or non-selective, pre-emergent or post-emergence, and contact or systemic.
Selective herbicides are generally used on lawns and will kill certain target plant species (say broad-leaved weeds like dandelions) while not harming others (like turfgrasses) if used at rates according to the direction. If overapplied, or if applied when the plant you do not want to harm is under temperature or water stress, they may harm non-target species. A non-selective herbicide will kill all vegetation it comes in contact with.
A pre-emergent herbicide is used to prevent germination of certain weed species before the weeds germinate and the seedling emerges. This type of herbicide would be found in a crabgrass preventer. It is essential to water the pre-emergent herbicides in, as they form a chemical barrier on top of the soil which inhibits annual weed seed germination for a period of six to eight weeks or so.
Post-emergence herbicides would be used when the unwanted plant is in full leaf. Ideally they should be applied and left on the weed species for several hours to a couple of days before watering or mowing for greatest control. The chemical herbicide needs time to be taken in by the plant and translocated to the root.
Contact herbicides kill mainly just the part of the plant that they are applied to, while systemic herbicides are absorbed by the plant and then taken into the root system. Some of the organic herbicides, like acetic acid, are contact herbicides. Herbicides are not for everyone. If you do decide to use one, always follow the directions and safety precautions thoroughly.
Another option for some areas is to use a flame thrower. There are small portable units that are useful for weeds in walkways and patios and in other areas where there is little danger of igniting mulch or other flammable materials.
Do your best not to let weeds go to seed, as most are prolific seed producers. Get rid of them when young and top your garden beds with mulch. Seed any bare spots in the lawn so weed species can’t move in. If you have questions about weed control, or on other indoor or outdoor gardening topics, call the UConn Home & Garden Education Center, toll-free, at 877-486-6271, visit www.ladybug.uconn.edu, or contact your local Cooperative Extension Center.