ASK THE GARDENERS

Q Would you please name some shrubs that would grow into a good thick hedge and would provide food for birds, also? The area is in full sun. J.McK. St. Paul, Minn. Four of the best would be: (1)high-bush blueberry (Vaccinium corymbosum), fruits in fall; (2)Siberian dogwood, also called shrub dogwood (Cornus alba siberica), fruits in July; (3)hemlock (Tsuga canadensis), evergreen that has seed-filled cones all year; (4)viburnum, European cranberry (Viburnum opulus), fruit matures in fall and provides food all winter. Q Would you please send your leaflet on ``Garbage Can Composting''? Also, would you please tell me how I can improve my soil? It is clay, clay, clay! I have not been able to grow any kind of flowers or vegetables successfully. K.A. Chicago

The secret is to add organic matter to your soil. Clay soil has fine particles that pack together so plant roots cannot ``breathe.''

Humus (organic matter) makes larger particles and adds porosity. It encourages earthworms to live in the soil and help revitalize it.

The decomposed household waste from your composter will be a boon, as will leaves, grass clippings, and other yard waste. You may not have it in Chicago, but rotted manure makes a fine soil amendment.

Cover crops are excellent soil builders. Oats can be sown in early fall - ryegrass in July or August, buckwheat in July. These are plowed under in spring. There are other crops, such as clover or alfalfa, but lime must be added in order to make soil alkaline for them to grow well.

Your agricultural extension agent from your state college can have your soil tested and make fertilizer recommendations.

Don't worry about adding too much organic matter. A friend of ours adds two to three feet of rotted leaves and other humus every year. He has the best garden around.

Q Is there a product that can effectively control weeds until a ground cover can establish itself? B.S. Walsenburg, Colo.

We do not recommend chemical weedkillers.

A number of manufacturers are producing woven matting called weed barriers. Many are made of polypropylene. Landscapers are using it extensively. It is easy to lay, and it's simple to slit for inserting plants into the soil.

A mulch of wood chips or shredded bark can be used to cover in-between plants, if desired. Ground covers can spread, and their roots and water can penetrate it, but weeds cannot grow up through it. It is now available in most garden stores.