Autumn Leaves: Should You Collect Them or Leave Them in Place?
We love to watch autumn leaves as they morph from green to red, orange, or yellow, but once they fall to the ground, many gardeners no longer see them as beautiful, but instead as a mess to be contained and removed.
Often, however, it's best to leave your leaves in place. Leaf litter contributes to soil health, and it's a critically important habitat in the life cycles of insects like bees, butterflies, and fireflies, as well as larger animals like salamanders and toads.
Using blowers or other power tools to remove leaves from your garden burns fossil fuels and generates air pollution, not to mention noise pollution, and sending your leaves to a landfill contributes to methane emissions. Raking leaves by hand can be time consuming and comes with environmental costs, too. Even if you live in one of the select NYC neighborhoods where leaves are picked up curbside for composting, the trucks that come and collect those leaves are producing exhaust fumes.
How do you decide when to let leaves be and when to remove them? Here are some questions to help you decide:
Are the leaves on your hardscape?
Hardscape includes paved areas of your garden like stone or brick and you should always remove any leaves (or other organic matter) from these areas because they can become slippery and dangerous, especially after rain or snow. Instead of taking them to the curb, consider moving all or some them to your garden bed instead. Read on for more advice on that.
You could also transfer some to your compost bin if you compost at home. If your bin can’t accommodate them all now, consider keeping them on standby for future use.
Could your plants get smothered by the leaves?
If you have a garden bed with small plants and large fallen leaves (bigger than those on your garden plants) or a large volume of them, the leaf drop could smother the plants. In BBG’s Rock Garden, for instance, there are several beds with very small evergreen succulent plants like stonecrops and hens and chicks. I move the fallen leaves from those beds so they don’t block the plants’ access to sunlight and air circulation, especially important for evergreens, which don’t go into winter dormancy.
If you have a bed with mostly large, vigorous plants or an area with mostly bulbs (which are dormant for the winter), there is no need to remove the leaves. In fact, leaving them in place could help protect your plants and suppress weeds.
Lawns, on the other hand, can be smothered by a heavy covering of leaves. If you are trying to cultivate a vigorous lawn in a spot that receives a lot of leaf drop, it is best to remove most of it. A light amount of leaves can enrich the soil without smothering the plants. To further help the fallen leaves do their winter work, you can chop them with a lawn mower. Again, consider moving excess leaves from your lawn to appropriate garden beds or your compost bin instead of putting them out on the curb.
Do you want your plants to self-sow?
If you are trying to grow self-sowing plants, a heavy layer of leaves could inhibit the seeds’ ability to germinate. Conversely, if you are not trying to cultivate any self-sowing plants, any leaves not raked out of your beds may help to prevent weed seeds from germinating.
Do the pH needs of the plants you are cultivating match the pH of the fallen leaves?
The pH level is important because it influences how readily the plants in your garden are able to access nutrients from the soil. Most plants have a range in which they will do well, and most common garden plants tend to do well in soil on the more acidic side of the spectrum (which is what you will usually find in the Northeast). Leaves from acid-loving trees, like oak and pine, will further acidify the soil over the years as they decompose. This will be particularly beneficial for more acid-loving plants like rhododendrons, heaths, and heathers.
But if you’re trying to maintain a bed with plants that need alkaline soil—for instance alpine plants like gentians and rock jasmines—acidic leaf litter will undermine your efforts. If your neighbor’s oak leaves and pine needles keep blowing into your garden, you’re better off moving them.
Can your garden accommodate the weight?
If you have a garden with a weight limit, like a rooftop garden, you should remove the leaves. Over several seasons, the gradual accumulation of leaf debris could make your garden exceed that weight limit.
Do the leaves harbor any diseases or pests?
Just as leaf litter can provide shelter and sustenance to beneficial organisms, they can also harbor pests and disease. If the plant that the leaves came from seems diseased or infested with pests in any way, remove its leaves and dispose of them.
Do your plants like rich soil?
Leaving the leaves is a great way to add organic matter to your soil. Most common garden plants thrive in rich, moisture-retentive soil with a diverse food web of worms, insects, and other organisms, so the additional organic matter will do a lot of good. Instead of removing the leaves each fall and then trucking in mulch each spring, save time, energy and money by just letting the leaves decompose and act as mulch.
If instead you have plants in your garden that prefer a leaner, dryer soil—say, desert plants (like ice plant) or prairie natives (like coneflowers)—you would do well to move at least some of the leaves to another area.
We often think of a garden like a picture—a static and unmoving tableau—and in response to that image, we make choices from a purely aesthetic point of view. If the leaves look messy, we remove them. But a garden is really an ecosystem where only a small part of what is taking place is apparent. So much is happening underground and inside the plants themselves. When you are considering what to do with the brown leaves in your garden this fall, don’t just think about how they look. Think about what they can do for your garden, and about what you can do for the environment, by letting all or some of them stay put.