Fall leaves are a great resource of nutrients for the garden, but if you use them incorrectly, they can rob your soil of nitrogen and make it difficult for plants to grow. This is especially true in a vegetable garden where you are trying to grow things quickly from seed.
In this post I discuss the decomposition of fall leaves and explain how to properly use them in the garden. In the process you might discover some interesting things about your compost pile.
How to Use Fall Leaves
What should you do with fall leaves?
Take Them to the Curb
From a financial position and an environmental position, this option makes no sense. The leaves are a great addition to your garden, and there is no point in giving them away.
Leave Them on the Lawn
Lots of people are now saying this is a good idea, but even if you shred them first with a mower, too many leaves on the lawn will kill your grass. This is only a good idea if you do it in small quantities.
Cover Garden Beds With the Leaves
This works great for most plants. The leaves keep the crown of perennials warmer and help collect snow when it does fall. Provided the leaves are not too thick, they can just be left alone in spring, and they will decompose. If you have thick layers, say more than one inch, you will want to remove some in spring as the plants start to grow again.
Some plants, like small alpines, do not want to be wet in winter, and a covering of leaves might cause them to rot.
Add Them to The Mulch Pile.
Another great idea that turns the leaves into future nutrients for the garden.
Make Leaf Mold
As I will discuss below, fall leaves have a high carbon level, which slows down their decomposition. If you simply pile up the leaves on their own, without adding extra high-nitrogen material, the fungi will slowly decompose the leaves into something called leaf mold. In a year or two this will make great mulch for the garden.
Bury Them In the Garden
This is a popular approach by people who like to dig in their garden. They cover it with leaves and then dig or rototill the whole thing so that the leaves are covered with soil. Some people do this in a perennial garden—I’m not sure how without damaging a lot of roots—but it works best in a vegetable garden because most of the plants have been removed during fall cleanup.
On the surface this sounds like a great idea. You are adding organic matter to the soil, which will decompose and release nutrients for future crops. The reality is different.
Decomposition of Fall Leaves
The key to this process is the C:N ratio, which is the relative amount of carbon to nitrogen. Microbes are most efficient with a ratio of 30:1, which is the number usually recommended for making fast compost.
The C:N ratio of leaves will depend on environmental conditions as well as the tree species, but the range for fall leaves is in the order of 35-85:1. That is way too much carbon. In order for microbes to decompose the leaves, they need to find another nitrogen source, which is usually taken from the soil.
If the leaves are used as a mulch, the nitrogen is taken from the top few millimeters of soil, which won’t affect plant growth. But when the leaves are buried in the soil, the nitrogen is taken from the soil next to each leaf. If this is next to a growing plant, the microbes will compete with the plant for nitrogen, and the plant usually suffers.
As the decomposition process continues, the C:N ratio declines, and once it reaches approximately 17:1, excess nitrogen becomes available to plants. When decomposition is complete, the ratio will be 10:1.
Burying fall leaves in the garden can result in nitrogen deficiencies in plants the following spring and summer. The degree of this deficiency depends on the amount of available nitrogen in the soil and the amount of leaves. One way to overcome this problem is to add nitrogen fertilizer to the garden in the spring, which will meet the needs of both the microbes and the plants.
It’s better not to bury them; use them as a mulch instead. This will prevent a nitrogen deficiency and preserve soil structure because you aren’t disturbing the soil.
Nutrients in Fall Leaves
What kind of nutrients do fall leaves add to your garden? Spectrum Analytic Inc. analyzed 100 municipal leaf samples collected from across New Jersey and found the nutrient values in the table below. The average NPK value would be 1-0.2-0.5. They also add many of the micronutrients, which should not be surprising since all plant material has about the same amount of these.
References:
- Nitrogen as a Nutrient; http://passel.unl.edu/pages/informationmodule.php?idinformationmodule=1130447042&topicorder=2&maxto=8
I cover my raised bed with fall leaves. Then use cardboard or old chair cushions to cover the leaves with. It helps keep them from blowing out and I believe it helps decompose them faster by holding moisture in. I then loosen the soil on top but don’t til. I haven’t had luck growing from seed I usually buy young plants and transplant with good outcome. Any tips?
Tips on what?
If you want to know how to grow from seeds have a look at these videos. https://www.youtube.com/watch?v=dirz0WIMQi0&list=PLq7hmpP9i05Ska3k7gaBCvNCT9gN_tYaj
I have covered my garden with 6to8” of leaves that I mowed and vacuumed with a leaf bagger , I was now going to plow it for next spring, do I need to do anything else or allow it to break down and till it in for planting next spring? Thank you in advance.
I would not till anything – it is not good for soil. Just use them as a mulch.
Last fall (2020) i piled on about a foot of leaves in my veggie garden and in the spring of 2021 i tilled them into my soil. The soil looked beautiful after tilling it 4-5 times but when i planted in May nothing grew and what did was pale green leafage. after reading posts online i seem to have taken the nitrogen out of the soil. My question is, How long will it take to revitilize the soil and is there anything i can do to help it? will milorganite help? thank you in advance John J.
You did not take the nitrogen out of the soil. The microbes digesting the leaves have absorbed it because leaves have a very high carbon:nitrogen ration. All you have to do is add more nitrogen or wait until the leaves are decomposed.
I did the same thing (100% maple leaves). Nothing grew the following summer. Didn’t know about adding nitrogen to fix it.
The following summer, mostly back to normal after a years dormancy.
I’ve seen posts concerning using maple or oak leaves in large quantity.
Maple makes up most of our leaves, followed by oak. Is this a problem or a myth?
No problem at all – every seen a maple forest?
Thank you for your quick reply. Great to find a really helpful site!
I had a bin 5 ft by 4.5 feet filled 3 ft deep with twice mowed leaves. This spring I would mow the lawn and save the clippings. I mixed them with an EQUAL VOLUME of said leaves. I have compost in about 3 weeks that is usable. True that it might not be completely decomposed, but it will grow stuff. This was much better than using the leaves or grass clippings as mulch. Yes mulch helps keep in water… but it is not broken down instantly. best garden I ever had this year.
I mulch leaves. Put in compose pile. My front yard 180’x200. On last mow I cover leaves in compose pile. I use raised beds due to serious clay soil.
Question would I be better served using grass clipping in beds to over winter. Btw I use straw bails for fall decor’. Have 4 I usually just mulch them and cover beds. My problem is I get blossom end rot. On Roma’s ( i know normal). Did lime heavy solution seemed to fix it. Next my tap water test at 8.0. I know killed all my fish in tanks. Green funk. Any suggestions .
I would leave grass clipping on the grass, and leaves on the beds.
Last year I had a problem with my bold displays of tulips in 2ft diameter, 2ft deep pots. Potentially too heavy to lift. I devised a scheme to completely fill the pots with autumn leaves, tamp down with my foot and apply a handful of general fertiliser, partly top up with soil, plant bulbs, cover with soil, top dress with another handful of fertiliser
Result magnificent bulbs never better, light containers and when the tulips eventually died down a wonderful soil/compost mix for further use as a potting compost
I wrote my version of how to use Autumn leaves in this post http://www.nodiggardener.co.uk/2018/12/what-to-do-with-autumn-leaves.html
I use shredded leaves for mulch. Shred leavesin the fall, store them over winter in a compost bin, apply them to the veggie garden as mulch during the next growing season, leave that mulch on the beds over winter, and incorporate it into the top layer of soil along with some finished compost the next spring. I find that my previous years leaf mulch is well broken down by the time spring rolls around. Ant thoughts on his process?
You are in effect composting the leaves in the garden – great idea.
Leaves on flat surfaces like lawns do blow off said surface, if not taken into the soil by worms before that happens. You can, of course, mow them up, but adding them to your borders, or letting the wind do that is easiest and useful. No need to make work for your self….
lawns are not really flat and although some blow off in open areas, they don’t in all areas.
I was so pleased to see your discussion of leaf mulch. My soil base is the sand and gravel used as fill, when the house was built. For 20 years I have used leaves applied in the fall, to turn a very large mixed garden into what is essentially, leaf mold. Once on, all I ever do is pull the mulch back a bit from the plants in the spring. It took a long time to make a fertile, spongy soil, but worth the patience. The forest has been doing this for millennia. It is gratifying to be finally in tune with the prevailing wisdom.