Is it all right to leave fallen leaves in my foundation beds?
William DiLeo, Falls Village, CT
Shreadded leaves make good mulch for winter plantings.
Photo/Illustration: Steve Aitken
Cheryl Cadwell, a University of Rhode Island master gardener and owner of Bittersweet Cottage Gardens, replies: As autumn drops its red and gold glory all over our yards, it would be nice to take the easy path and rake those leaves into the foundation shrubbery or leave them where they fall. A few stray leaves under your foundation plants won’t be a problem. In large quantities, however, the leaves will pack down and form a dense mat that can prevent sufficient moisture and air from reaching the soil. Even in winter, plants need an adequate supply of water and oxygen to survive.
As the season progresses, the leaf mat absorbs moisture and turns into a dense, soggy mass lying against the stems of your plants. This constantly wet environment can soften bark and break down stems, making them vulnerable to pests, disease, and frost breaks.
A good but slightly labor-intensive solution is to rake all the leaves out into the lawn and shred them with the mower. The result will be a tidy, loose mulch that won’t pack down; water and oxygen will be able to move into the soil, and the roots of plants will have protection. A bonus is that shredded deciduous leaves break down in just a few months, quickly adding organic matter to the soil, which is always a good thing.
There may be some concern about possibly altering the pH level of the soil by using maple or oak leaves. Changing the pH level of the soil can inhibit a plant’s ability to absorb some nutrients. I have used these leaves as my only mulch for two decades, however, and my soil tests have been consistently in the neutral range.
If pine needles make up the majority of what is dropping into your beds, don’t bother to shred them. The shape and rigidity of the needles will keep them from packing down, and they make an excellent mulch. Pine needles break down slowly; adding lime every few years will counteract any acid buildup. Let a soil test be your guide to any adjustments.
Come spring, most of the shredded-leaf mulch should have decomposed, but if there is still a layer of leaf material, rake it out. Pests and disease may be lurking under this cover.