Organic mulch is the key to gardening under trees
As a younger gardener, I preferred gardening in the bright, toasty sunshine. As I get older, however, I would rather garden under trees, their branches offering respite from the sun and heat. But gardening under trees poses unique challenges.
The roots of trees grow horizontally, extending far beyond the drip line of their tree. In heavy clay soils, like most of us have, tree roots are often not more than a couple of feet deep. Feeder roots grow upward from large anchor roots and take up water and nutrients near the surface of the soil.
Mature trees are thirsty, robbing the soil of more than a hundred gallons of water to quench their thirst each day. In addition, the tree's canopy prevents rainfall and sunshine from reaching the ground underneath it. These conditions do not create a hospitable environment for growing perennials. Do you still want to garden under trees?
Care must be taken when planting under a tree to avoid damaging too many roots and causing severe injury to the tree. Instead of cultivating the entire area under the tree and amending the soil with organic matter (as it often recommended when preparing a new bed), plant perennials in spaces between roots, amending the soil as you go.
Never add a deep layer of soil over tree roots to create a new bed. It may make it easy to plant without damaging roots with a shovel, but instead, it may smother the root system of the tree. If some soil is going to be added, use good quality top soil mixed with large amounts of organic matter and only add a couple inches at a time, giving the tree's roots time to adjust. Of course, over time, the roots will move up into the new soil. Do you still want to garden under trees?
I did, and I found the secret for gardening under trees — organic mulch. Organic mulch breaks down over time, creating a growing environment rich in nutrients for perennials and the trees.
Letting leaves remain where they fall is one example of organic mulch. Leaves from beech, honey locust, hornbeam and oaks break down quickly, but the leaves of some of my trees are large and take longer to break down. Too many of these left under trees may suffocate perennials, so I remove the first half that fall and let the rest stay where they fall.
An ideal way to use leaves as an organic mulch is to rake and then shred them before returning them to the garden. Leaves can be put through a shredder or run over several times with the lawn mower.
Homemade compost is another source of organic mulch. Lawn clippings (free of chemicals), garden debris (free of disease), shredded newspaper and kitchen waste, like coffee grounds, fruit and vegetable peels, can all be turned into nutrient-rich compost.
Shredded wood chips are another option. The finer they are shredded, the faster they will break down. Shredded wood chips are very attractive and can also be used to create walking paths through the garden.
In instances where a garden under a tree is desired but is not practical or possible, consider a mulched sitting area with a garden bench and a collection of containers. Combine hostas, ferns and shade-loving annuals in gorgeous designs of color and texture. Another small space nearby could be carved out for an old wheelbarrow filled with annuals and a birdbath. Or bring in a group of old stumps and create a charming fairy garden.
• Diana Stoll is a horticulturist, garden writer and speaker. She blogs at gardenwithdiana.com.