Gardening under mature conifers and big leaf maples

Asked May 21, 2019, 12:49 AM EDT

I am wanting to plants shade tolerant shrubs and perennials in an a area of very compacted soil with many exposed roots from mature Douglas Fir and big leaf maples. Info on internet is contradictory, ie, don’t cover roots, cover with 4-6 inches of compost or bark chips twice a year, don’t plant near big roots, etc. can you advise?

Washington County Oregon shade gardening

4 Responses

To plant successfully under conifer trees recognize that the area will probably have slightly acidic soil from the needles which are mildly acidic. Compacted soil will need to be gradually built up and drainage improved. The chosen plants need to be shade tolerant, and be able to withstand dry conditions. Trees take up an enormous amount of water, leaving the soil around them very dry. That said, many shade-tolerant, drought-tolerant plants do well under trees. This article has a good discussion and includes several plant options, Plants that grow well under pine trees https://www.backyardgardenlover.com/plants-that-grow-well-under-pine-trees/.

Trees have 2 main kinds of roots, non-woody and woody. Non-woody, fibrous roots appear in the first few inches of the soil. Their purpose is to absorb water and nutrients. They are sometimes called "feeder roots". Woody roots are large, lateral roots. They exist in the top 8-12 inches of the soil. Because they are perennial, growing with annual growth rings, they can become exposed. The purpose of woody roots is to support and anchor the tree, as well as transport water and minerals to the body of the tree. They also store carbohydrates. This article has additional information, Tree Root Systems https://hortnews.extension.iastate.edu/1992/4-1-1992/treeroot.html

To plant around exposed roots use small plants at first that can develop in the spaces between the roots. Adding a large amount of soil to the area will suffocate the trees' roots. Mulch the area after planting with a couple inches of loose compost or bark dust. This will retard soil moisture evaporation, add nutrients, improve drainage and allow the roots to become established. Make sure you keep the tree trunks mulch free for at least 12 inches from the tree, as the trunk needs to "breathe". Water weekly when weather is dry, even more often when conditions are hot and dry. A soaker hose will provide long slow moisture. Avoid fertilizing for the first year, as it encourages top growth rather than the roots which need to develop. Mulch the area every spring with 2-3 inches of organic matter like compost, shredded leaves, well-rotted manure, etc. The exposed roots can be covered as well. Soil organisms will gradually bring the nutrients down into the soil..

There really is quite a selection of plants that will work in your situation: sweet woodruff, hostas, ferns, bleeding heart, rhododendron, hydrangea, wild geranium, violets, trillium, hardy cyclamen. Great Plant Picks https://www.greatplantpicks.org/plantlists/search/, a site managed by PNW nurserymen has great information, pictures, growing conditions, size, etc. and is specific for our area. Look at shade tolerant and drought tolerant lists for plants. The main goal is to use plants that are of the right size and type to be happy in that environment; and to ensure they have access to enough moisture to thrive. This is especially important during the first couple of years while the young plant

Thank you so very much, Anne. The is very helpful! And the links were also great. I really appreciate this service, your time and dedication!!

Connie

Thank you so very much, Anne. The is very helpful! And the links were also great. I really appreciate this service, your time and dedication!!

Connie

Thank you so very much, Anne. The is very helpful! And the links were also great. I really appreciate this service, your time and dedication!!

Connie