In addition to fall being a great time to get new plants in the ground, it can also be an ideal season to fertilize your lawn, trees, shrubs, and perennials. But you have to do it correctly: During these cooler months, plants are slipping into dormancy and not actively growing. Depending on how severe or mild your winter is, they can be anywhere between completely dormant to growing very, very slowly. If you fertilize right, you’ll be giving them the best send-off to their winter sleep.
Before you start, you may want to get in touch with your local cooperative extension. They can help you get a soil test (you can’t help your plants if you don’t know what they need). And they can tell you the first frost date for your area (for practical purposes, fertilizing should be done before the first frost). They know your climate best and can give you advice specific to your location.
Note: We don’t recommend using synthetic fertilizers because of the large environmental impacts associated with them, including water contamination from run off and decimation of soil microbes. Restoring soil health naturally should always be the first option.
Here’s what you need to know about fertilizing (naturally) in the fall.
For the Lawn
The best and easiest way to fertilize is to do one last mow with a mulching mower and leave the clippings on the lawn. Mulching the clippings back into the lawn can provide up to 50% of the needed nutrients for the grass. To make up the rest of what your lawn needs, there are two low-cost and environmentally sustainable ways to fertilize. First, you can aerate the lawn and top dress with compost. Second, if you have fallen leaves, mulch them into the lawn as well. Just remember to rake them around so they aren’t too thick. It is a smart idea to keep the nutrients created on your property, on your property. (See Ask the Expert: Doug Tallamy Explains Why (and How to) Leave the Leaves.)
A more expensive, less eco-conscious option is to use organic lawn fertilizer. While organic fertilizers are certainly better than chemical fertilizers, there are still manufacturing and transportation costs to the environment. If you go this route, follow the directions exactly. More is not better.
For Trees and Shrubs:
A closed loop is the best type of fertilizer. Keep the leaves from the trees under them. They have everything the trees need—for free. They help on so many levels. They act as mulch and keep the moisture in the soil, which in turn helps the microbes that break down the leaves, making their nutrients available to the trees. The leaves also become winter homes for good bugs. Just be sure to keep the root flare exposed; piling the leaves up the trunk can cause can cause the bark to rot. No trees on your property? Organic compost is your next best choice.
For shrubs that were healthy over the growing season, a leaf well around the base will be enough. If they didn’t do well over the summer, they may need a bit of help. Aerate the soil and add some compost and water well.
If you want to add store-bought organic fertilizer to your tree or shrub, you may want to consider consulting with an arborist first. It’s easy to over-fertilize and cause damage. Leave it to the professionals.
For Perennials:
Yes, leaves again. Really. And compost. Both the leaves and the compost break down slowly. Nobody is in a rush here, it’s winter and nothing is growing. The idea is that the nutrients will be ready and in a form the plant can use once it wakes up in the spring. If you’re concerned about burying your plants too deep in leaves, lightly cover what remains of your almost dormant plants, but pack the leaves thickly around them.
There are no other real options. If you use synthetic fertilizer while they are going into dormancy, they could come out of dormancy early during an extended warm spell—and then when a cold snap follows, the new growth may be killed. This can weaken the plant, causing it to fail to thrive in the spring or even die.
Our gardens are part of a larger ecosystem, so it’s important to prioritize soil health and natural methods over synthetic fertilizers. Aeration of compacted soil and addition of organic matter will have a better and a longer-lasting effect on plant health.
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