I received this question in the summer:
I enjoyed reading about the good in leaving the fallen leaves in the Fall, and I am wondering what you suggest for them in the spring and summer. Do you recommend that they stay on the lawn then, too?
-Frank
And here was my answer to this question:
So great to hear from you!
What a great question about leaving the leaves. As mentioned in the article, the leaves and debris are a valuable source of nutrient and fertilizer for the plants and micro-organisms. And so, it would be best to leave this mulch on your garden beds for the spring and summer as well. Essentially, leave the mulch on year round! The wee creatures that live in the soil will continue to feed on this plant matter and break it down further and further into humus. These creatures need food year-round, and in the summer with all the fresh green growth happening, there is not much opportunity for eating fallen plant debris unless it was left from the previous fall.
Admittedly, leaving a healthy mulch layer does leave the door a little open for some pest soil organisms, such as slugs, to flourish in your garden. However, if habitat for their predators, such as snakes, hedgehogs, raccoons, crows, snakes and some types of beetles, is provided then slug numbers can be controlled far more easily. Sort of a circle of life type of thinking, right?
From my experience, the mulch as whole leaves doesn’t actually last much past late spring or early summer! Those little creatures are indeed hungry little critters and will work their way through much of that debris and break it down fairly quickly. This is especially true if the garden is pretty spare and doesn’t contribute much to that mulch layer, and even more so if one lives in a climate that is rather mild, such as the Pacific Northwest where I used to live.
Having large trees is a bit of a different matter, though. Some of those trees drop an amazing amount of leaves and that will persist a fair bit longer.
Also touched on in the article, this mulch layer has the added benefit of sheltering the soil from the elements, such as harsh spring rains/storms and then the strong baking summer sun. This translates into less erosion and increased water holding capacity. It will also help suppress weeds in the garden, leaving less of a need to weed during the growing months.
I would not recommend that leaves be left on a lawn unless they are mowed over several times with a strong mower or put through a debris mulcher, which will break them down into much smaller pieces. Otherwise as whole leaves they will smother the grass and eventually kill it. This is especially true for trees such as black walnuts (juglone hormone) and black oaks (high tannins).
Trees/shrubs and grass actually have a fairly antagonistic relationship as grass is what is called allelopathic. Allelopathy is when one plant uses either physical or biological methods to reduce competition from other plants that would grow near it (such as black walnut and black oak mentioned earlier). In the case of grass, most species of grass put out hormones that affect nearby plants. This is why ryegrass and other green manures work so well to suppress weeds in crop rotation systems on farms. Trees and shrubs fight back by dropping their leaves and smothering the grass. We interrupt that subtle battle by removing the leaves and allowing grass to creep right up to tree trunks.
This is one of many reasons why young trees planted in orchards, boulevards and most places in the city often struggle to get established. It is essential to maintain a sizeable grass-free zone around tree trunks (far bigger than the scant foot they are given these days), at the very least when the trees are quite young and more vulnerable to disease and stress.
In the end, it might be best to simply use the leaves to cover the bare soil in garden beds, or compost them separately and then spread that compost back onto the lawn when it is a fair bit finer and more broken down.
In summary, with careful consideration, leaving the leaves is an all-around amazing way to improve your soil and feed your soil organisms year-round.
If you have a question you think I could help you with, please feel free to connect with me!