Are You Making These 5 BIG MISTAKES with Fall Leaves?

It's almost fall and the leaves are coming. They're a great resource for the garden if you use them correctly, but there are many mistakes that you can make and a lot of myths surrounding fall leaves. Should they be left on the lawn? Is it okay to compost leaves that have black spots on them like on maple trees? What about other types of fung? Is it okay to compost those? Can you leave leaves on the garden bed and will those harm your plant? Do leaves rob your soil of nitrogen? I'm going to have a look at all of these and a bunch of other myths. Should leaves be left on the lawn? The simple answer is no, but there are some exceptions. Cool season lawn grass grows best in spring and fall when temperatures are lower. They need sunlight to grow and leaves can reduce that to such a low level that grass dies. Having leaves on a lawn is no different than covering it with cardboard to kill the grass. It is best to have no leaves, but there are a few exceptions. The odd leaf will not kill the grass because light can get around the sides. Small leaves like the ones from birch trees are not nearly as big a problem as large maple leaves. Small leaves from perennials are also okay. If you can't see most of the grass, it's a problem. Should you compost infected leaves? Some maples get black spots and it is recommended that you don't compost. Leaves with powdery mildew are also a concern. The fear is that if you use such infected leaves in your garden, even after composting, the fungal spores will survive and infect plants in spring. Surviving fungal spores will indeed infect plants the following year, but not all fungi can survive a cold winter. Although the logic seems sound, it really does not matter much in most cases. By fall, virtually every leaf in the garden is infected with some type of fungi, even if you can't see anything on the leaf. If you don't use infected leaves, you would not use any plant material. Not only are the leaves infected, but fungal spores cover every inch of soil, mulch, and leaf debris. They are everywhere. Fungal spores move long distances by air currents, and all the fungi in your neighborhood will end up in your garden. No matter how careful you are, you will have powdery mildew and black spots next year, so you might as well get some benefit from the leaves. Besides, this is what nature does. Nobody removes infected leaves from the forest floor or meadow. Leaves are good for flowerbeds. Cover your flowerbeds with whole leaves, or even better, shredded leaves. They keep the soil warmer and protect plants. They also keep moisture in the soil, which is important, unless you have very wet winters. Perennials, bulbs, and tree roots all benefit from a blanket of leaves. If you have a thick layer of leaves, you can remove some in early spring before new growth starts. If the layer is less than 3 inches or 7 centimeters, just leave them as mulch in spring. They will slowly decompose by mid-summer. Can leaves smother and kill plants? Yes, provided your winters are not too wet. The leaves will not harm the plants in winter. However, if the layer is too thick, they can prevent short plants from growing properly the following spring, and may even kill them. Most plants have no problem poking their way through a thick layer of leaves. Except for very tiny rock garden plants, a layer that is less than 3 inches or 7 centimeters will not harm plants. The exception to this rule is gardens that have a wet winter, or plants that are very sensitive to water around their crowns in winter. Our winter can be wet, so I keep leaves off the rock garden because these plants are both small and tend to be sensitive to moisture. The rest of the garden gets leaves. Do leaves rob soil of nitrogen? This is a common belief, but it is not true, provided the leaves are sitting on the soil. Since leaves have a high CN ratio, they have little nitrogen relative to carbon, and if they are buried in soil, they do compete with plants for nitrogen. They should only be used as a mulch. Nature will decompose them and take them underground when appropriate. Mulching leaves with a lawn mower. Is this a good idea? Raking leaves is better for the environment than mowing them. Gas mowers cause pollution. While raking keeps you healthier. You might think battery-operated mowers are okay, but remember that the electricity they use needs to be produced somewhere, and that has environmental consequences. Is shredding better than raking? Some of the claims for chopped up leaves are not valid. For example, improves the health of your soil. Both shredded and unshredded leaves do that. Shredding does speed up the decomposition process by a few weeks. Beneficial for insects, critters, and microorganisms. Shredding probably does more harm to insects and critters than not shredding. Saves money on garbage bags. This has nothing to do with mulching. Create mulch for other areas of the garden. Leaves work just as well. Saves time and effort since mowing is quicker. This one is true. Shredding does allow you to leave the leaves on a lawn, provided you don't have too much material. The best option is to rake the leaves off the lawn and use them somewhere else in the garden. If you want to reduce the amount of raking, mow the ones that you can leave on the grass and rake thicker layers for use in the garden or compost bin. Lawn mowers work better for mulching if you use a mulching blade and cover the exit hole. You can mow six inches of leaves. There are quite a few sites that repeat the claim that you can mow six inches of leaves at one time and leave them on the lawn. This is a myth. A mulching mower does not work on six inches of leaves at one time. Less lawn weeds. Mulched leaves can be left on the lawn, provided you do not leave too many. When you are done, you should clearly see the grass. Michigan University studied the effects of leaving mulched leaves on the lawn and found that after three years, they needed to add less fertilizer and there were fewer weeds. The chopped leaves cover bare spots in the lawn, keeping light from reaching the soil, which reduces weed seed germination. It can dramatically reduce dandelions and crabgrass. Composting leaves. Fall leaves have a fairly high CN ratio of 30 to 80, and there are a couple of different ways to compost them. Produce leaf mold. Pile them up and let nature take care of them. This method is easy and produces a nice compost, but it is a slow method. Use a traditional compost bin. Provided the leaves are mixed with enough greens, this makes compost fairly quickly. A smaller compost tumbler can also be used, but it is a bit slower because it never heats up properly. Wormy compost. The worms like fall leaves, but you can only compost a small amount this way. Is composting a better option than just mulching? All of these methods eventually produce the same nutrients and provide about the same amount of carbon, so they all benefit the garden equally well. Faster methods start helping soil sooner. That is really the only difference. Should you compost black walnut leaves? As you may know, black walnut trees release a chemical called juglone, which is allelopathic and has been shown to prevent some plants from growing. Should you compost such leaves? Juglone decomposes in a matter of weeks when exposed to air, water, and microorganisms. Composted walnuts may have an effect on seedlings, so you might want to keep them out of your vegetable garden, but they do no harm in the rest of the garden. They might even help keep wheat seeds from germinating. Do you need fall fertilizer? I found this false claim. The nitrogen boost from mulched leaves is such that you don't even have to fertilize in the fall. Fall leaves have a low level of nitrogen, so they are not going to add any to your lawn. In a non-tropical climate, fall leaves sitting on the surface of the soil won't even decompose for a year or more. You may be able to reduce fertilizer in future years, but not in the short term. In fact, adding nitrogen fertilizer will help the leaves decompose faster. Those are some of the main myths. Now let's have a look at some other ones. Microorganisms break down the leaves and make your soil richer. Now that's true, but in colder climates, none of that happens in the fall and winter. You have to wait till next summer before the microbes become active. Worms also get in the action and start decomposing worms. Now that's true as well, but not during the winter. They're hibernating. Mulched leaves provide plant roots with nutrients. Well again, there's some truth to that, but that only happens after the leaves decompose, and that can take years. This is not a fast process. If your plants are suffering because they don't have enough nutrients, fertilize them. The leaves are a long-term feed and work best in a year or two. Mulched leaves will decompose and disappear from your lawn by next spring. That's not true. In colder climates, when you mulch the leaves, the particles get smaller so you don't see them, but they're still there. They really haven't changed. You just now have little bits of leaves. Nothing happens during the winter. Any decomposition will start next spring and summer. I'm in zone 5, and my leaves look the same in spring as they do in fall. Nothing happens over the winter. But they are good for your garden. Now if you're interested in some more myths, have a look at these videos here. Happy gardening.