Leaves as Fall Fertilizer

It’s a bright sunny morning as I write this column, the wind has been whipping leaves off the trees and there’s whitecaps on the water. My tomato support cages were blown over this past weekend and it looks like the vegetable garden has finally gone down for the season. The leaves are nicely covering the ground and pretty wet after all the rain we’ve had so they’re not blowing too far at the moment. My plan this week is to run the lawn mower over them to blow the bits onto the new shade gardens. And that of course got me thinking about how to use leaves in the garden.

We already know that the single best use of leaves is to return them to the garden soil around the trees. Doing this will keep your trees healthy and happy. Given that grass under trees never grows very well anyway, making sure the leaves are chopped up and left under there is the single easiest way of keeping a tree healthy. It always amazes me that folks take away the leaves in the fall, never feed the tree in the spring and wonder why the trees get sick or don’t grow very quickly. The deal here is that allowing tree tree leaves to stay around the base of the tree is the single best thing you can do for your trees.

I know. You’re afraid of smothering out the grass. Well, if you have anything other than maple or poplar trees, this isn’t a major concern. Do run the lawn mower over top of these leaves to chop them up and the grass (such as it is in the shade) will be just as happy with the extra organic matter as the trees are. If you have large leaved trees, the leaves will indeed mat down and prevent grass from emerging. So chopping them up is step one and blowing the extra leaves onto the gardens is step two. The perennials and vegetable transplants will benefit from the extra organic matter and your lawn won’t suffer from being matted under leaves. I note that matting leaves is one way that maples deal with the competition; they simply smother it.

The second thing I’m coming to understand is that there are some chemical effects of leaves that act to delay the germination of some seeds. This is true of many plants, from evergreens to deciduous plants. The hormones in the leaves or needles work in the ground to delay the germination of competitive plants. It is only when the leaves are several years old that they begin to lose their ability to stop seeds from germinating (the hormones wear out). So a layer of leaves under and around trees also acts to stop weed seeds from germinating. This little know fact is why you want to be careful about adding a lot of fresh leaves to vegetable gardens when you’re starting a lot of your plants from seed. Started plants or transplants are not bothered by these chemicals but seed germination is slowed down or stopped. Personally, I love getting rid of weeds in my perennial beds so a layer of chopped-up leaves is exactly what the doctor ordered.

If you have a great many maple trees and you want to have a lawn around them, then yes, you’re going to have to rake up these leaves because the excessive layers of maple leaves will really slow down grass. But these leaves should then be composted and the compost spread under the trees if you want the trees to thrive and continue growing. In the larger scheme of things, a tree is either healthy and growing or dying. There’s no middle ground. Handling leaves properly and ensuring the composted leaves get returned to the trees is the first step in long term tree growth.

I also note that with the changes coming to the herbicide and chemicals available to Ontario homeowners next spring, the first line of defense in your garden is going to be compost and leaf mould. If you have large amounts of this material now, then you’re already ahead of the curve in getting ready to make the transition to organic gardening. You see the core component of a great garden, a weed-free lawn and garden health without chemicals, is compost. And starting by chopping up and collecting leaves this fall is an excellent first step.

A better first step if you don’t have tree leaves is to plant trees now. There are some great deals going on and you can plant deciduous trees right up to freezeup. Not only will this give you a source of garden leaves in the future, it will increase the value of your property now. Numerous studies show that trees increase property values and that each tree adds several thousand dollars to the value of a home. Not only that but several studies point out that property owners who have trees on their properties tend to get along better with their neighbors and tree lined neighborhoods are seen as better places to live. And to make the entire property value thing even greater, it is now understood that trees even work to prolong the life of nearby roads and sidewalks. The shade from trees cools down the roads and sidewalks lessening the impact of tires and wear. The hotter the asphalt or concrete, the more likely it is to wear and produce dust from traffic so trees actually protect infrastructure instead of being a problem for it.

Bottom line. You really want to get out there, save your leaves and plant even more trees. Your garden will thank you and so, it turns out, will your friends and neighbours.