COLUMBIA, Mo. -Over time, a sunny garden may become a shady one as surrounding trees and shrubs mature.

"Landscapes change their degree of shade, making it a challenge to grow garden plants," said Chris Starbuck, University of Missouri Extension horticulturalist.

"Analyze the degree of shade in your garden periodically to determine if changes in plant materials may be needed," he said. "Choose plants that do well in less light."

Shrubs like junipers and lilacs require full sun and will decline as shade increases. Replacing them with shade-tolerant species like azaleas, Japanese kerria or certain viburnums will improve the appeal of the garden considerably.

Plants growing in shade must cope with low light levels and poor air circulation and compete with shading trees for water and nutrients, Starbuck said. Shallow-rooted trees such as maples and willows are particularly troublesome.

Cool-season salad vegetables such as lettuce, spinach and radishes may benefit from light shading during the summer heat. Beans, beets, broccoli, cabbage, kohlrabi, peas, potatoes, rhubarb and turnips will grow in light shade, but not produce as large a crop.

Currants and gooseberries tolerate medium shade and still produce a crop. Bramble fruits such as blackberries and raspberries grow in light shade, but with reduced yields.

Adding organic matter to shade garden soil will help. In the typical landscape, removing leaves each fall disrupts plants' natural nutrient-recycling process. However, if leaves are not removed they can mat down and smother garden plants. Shredded leaves can be safely applied as mulch.

Another option is to compost the leaves and apply the compost in core-aeration holes or in small pockets dug in the garden, he said.

Don't haul in several inches of compost-rich amendment to till into the soil under shade trees. Some species, such as oaks, are extremely sensitive to changes in soil depth within their root zone.

Branches or walls that cast shade block air movement. Poor air circulation coupled with lower light levels means foliage stays wet longer.

"Most plant-disease problems are worse under these conditions. Plant farther apart in the shade to allow more air movement. Water with soaker hoses or drip-irrigation systems to avoid wetting the foliage," he said.

Removing lower tree limbs or entire trees and shrubs that are too crowded will increase air movement and light penetration below the tree canopy. This will reduce disease problems and allow a wider palette of plants to grow in the garden.

For more information, see the MU Extension guide "Gardening in the Shade" (G6911) at extension.missouri.edu/publications/g6911.

Writer: Robert Thomas