Tarp And Hoe Discourage Weeds From Moving In

Q: We removed all the plants from the back yard in preparation for later planting. How can we control weeds that come up before we plant?

A. Unwanted weeds return either from pieces of root and plant parts left in the ground, or from seeds emerging when newly exposed to light and good growing conditions. Shading or covering the ground will help. The ground can be shaded by a tarp, by putting mulch on the soil surface or by planting.

A tarp prevents plant growth by excluding light. Many weed seeds can remain viable for decades underground; they sprout when soil is turned and they are pulled up to light and air. If the top layer of seeds are allowed to sprout before the tarp is spread out, the exclusion of light will kill those new plants.

This technique will reduce the reservoir of weed seeds in the ground by knocking off one set of germinated plants. If, after doing this and leaving the tarp down for a few weeks, planting is accomplished with relatively little soil disturbance, you'll have fewer new weeds emerging into the final landscape.

If you can distinguish between annual weeds (those which complete their life cycle in one year) and perennial weeds (those, like dandelions, which live many years subsisting on stored energy in roots and other structures), your ultimate weed control choices will be easier.

All weeds are easiest to control when they are seedlings. If you didn't want to cover the ground with a tarp, but were willing to scuffle hoe the area regularly to dig or cut out new seedlings, you'd also get some control.

Mulch is a layer of 2 to 3 inches of organic matter - home-grown compost, commercial compost, leaves, sawdust, or chipped tree prunings - spread on the surface of the soil. It obviously works to shade out the weeds, just as a tarp will. However, some perennial weeds will grow through the mulch, and some annual weeds can germinate from seeds blown or dropped by birds on the mulch surface.

Mulches are excellent weed management options for established or new landscapes, and it would be advisable to add a mulch when the final planting is completed. Even if a few weeds emerge or sprout, they are much easier to control in a mulched area.

One of the best ultimate weed control techniques is to shade the weeds out with plants, installing a landscape that will fill in the spaces and prevent weeds from taking over. An effective combination is planting, plus mulch.

Spot treatment with herbicides can be used on perennial weeds that persist through the mulch. (Read the label carefully when using any pesticides.)

The last recommendation for controlling weeds is to be consistent, patient and persistent! (those ingredients don't come from retail stores.)

Q: Is it too early to prune fruit trees?

A: Fruit trees can be pruned anytime from about now until they bud out; complete all pruning before plants bloom. Do not prune when the temperature is below freezing.

If you need more information about pruning the home orchard, you can order a bulletin from Washington State University Cooperative Extension. Ask for PNW 400 "Pruning, and Training the Home Orchard." This bulletin can be ordered in King County at (206) 296-3900, in Pierce County at (206) 591-7170, and in Snohomish County at (206) 338-2400.

Gardening runs Friday in Scene and Sunday in Home/Real Estate. It is prepared by Mary Robson, area horticulture agent; Holly Kennell, Washington State University/King County Cooperative Extension agent, Susan Miller, integrated-pest-management specialist, and volunteer Master Gardeners.