13 Fall Soil Improvements You Can Apply Now
Autumn is the ideal time to add soil improvements. They’ll start to break down this season and continue working slowly during the cool months. In spring, you’ll enjoy fresh, crumbly dirt that’s prime and ready for new seedlings! Join native plant gardener Jerad Bryant to see the 13 fall soil amendments you should add today.
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Fall is the ideal time to add soil improvements to garden beds, raised beds, and containers. They’ll start breaking down this season before slowing their decay in the winter. Then, when spring warmth arrives, they fully decompose and mix in with the surrounding soil. Instead of waiting for amendments to break down in spring, you’ll be sowing seeds and planting veggie starts.
After the summer season, most soils are hungry for nutrients. Trees, shrubs, and annuals pull up minerals while decaying organisms eat through the leaf litter. Add soil amendments in the fall to feed plants, fungi, and bacteria, helping them thrive while they work together underground.
Many of these amendments also create animal habitats while they boost your garden’s dirt. Mulches like compost, leaves, or straw make cozy homes for bees, ladybugs, and worms to hide under during the winter. They stay warm and protected from predators below the organic materials.
These 13 amendments work well in home gardens whether you’re preparing beds for spring or repairing nutrient-poor soils. Apply them annually and your plants will thank you with disease resistance, lush growth, and hundreds of blooms!
Urban Worm Company Worm Castings
- boost plant growth
- speed up germination
- increase yield by 20-80%
- suppress pests and pathogens
- improve water retention
Compost
Compost is like black gold; it’s the perfect soil improvement! This material consists of old debris that worms, fungi, and bacteria turn into rich, crumbly soil. They consume the raw materials and turn them into smaller, more readily available versions that plants can access.
Create a compost pile by mixing green and brown materials at a ratio of 1:2 or 1:3. Greens are fleshy materials like grass clippings, food scraps, and animal manure. Browns are carbon-rich materials like paper, cardboard, sawdust, and fall leaves. The more greens you add, the quicker the compost decays.
Turn the pile daily with a pitchfork and maintain water moisture levels at 50%. You’ll want the compost to be moist, not soggy. After a few weeks, you’ll have a humus-rich amendment to add to your garden! Use compost for woody trees and shrubs, perennials, and vegetables. You can plant seeds or potted plants directly into it, or use it as a mulch on top of native soils.
Leaf Mold
Leaf mold is similar to compost, except it consists of leaves and no other debris! Simply stack a pile of fall leaves, water them well, and turn them every few days. You’ll have a black, crumbly, and humus-rich material that looks and acts like compost.
Whereas compost is extremely beneficial for fleshy plants, leaf mold aids woody ones that love carbon. Fall leaves have nitrogen in them and plenty of carbon. As they decay, they leach these nutrients into the leaf mold. Apply it to your soil to add a beneficial carbon source that plants can access directly.
If you just created a leaf mold pile this fall, it won’t be ready to apply this season. Leaf mold takes a month to a year to fully decompose; it also needs regular water and turning. Make a pile this year and you’ll have a fresh, black, and crumbly amendment next fall. What do you do if there’s a bunch of leaves and you don’t have time to make leaf mold? You use them as mulch!
Fall Leaves
Instead of spending time creating leaf mold, you can apply fall leaves directly onto the ground! They’ll improve it throughout the cool seasons as they decay slowly and feed soil microorganisms. Leaves are a boon for local wildlife; they form habitat space for tiny insect critters and they feed larvae, grubs, and worms.
If you have a lawn that leaves fall onto, you can chop them up with a lawn mower and mulch plug combo. The plug replaces a bag, letting the leaves and grass blades stay in the way of the blade. This chops up the debris into tiny pieces, and they feed your lawn as they decay.
The best way to use fall leaves is to simply leave them be! Let them fall where they may, or collect them and place them on your garden beds. They, like compost, feed both soil organisms and plants. Keep them out of black trash bags and leave them in your backyard instead!
Worm Castings
Worm castings are a dense form of worm poop! They’re the waste product worms leave after they eat raw scraps, plant material, and dirt particles. It’s crumbly, black, and rich in plant nutrients like nitrogen, phosphorous, and potassium. Find worm castings online, or create a vermicomposting system to make them at home.
Worm castings increase soil porosity, which makes it more absorbent and free-draining. This is crucial for plants to thrive—their roots need to breathe and drink water. Worm castings help soils work better for roots and increase pest and disease resistance for the plants that grow in them.
Use castings in containers, raised beds, or to amend garden soils. You can blend them into other mixes like compost or leaf mold to provide more nutrition per pound of amendment.
If you’d like to make worm castings at home, try an easy setup that uses gravity to your benefit. One example is a worm bag; this contraption allows for easy harvesting, rapid worm growth, and steady recycling of nutrients. Simply place scraps and plant debris inside the top and harvest castings out of the bottom after the worms eat the waste.
Grass Clippings
If you have a lawn, you’ll have plenty of grass clippings to manage. An easy way to upcycle them is to throw them back onto the soil! If you have perennial or vegetable beds, or trees and shrubs, you can add the clippings around their base. They’ll work like fall leaves, creating a mulch that decomposes into the soil.
Grass clippings can be damaging to soils if they’re in a thick layer. The grass pile can become anaerobic when it decays without access to airflow. It’ll be smelly, wet, and mushy. Keep the grass mulch layer thin and breathable to avoid rotten issues.
One other consideration for using grass clippings is weed seeds. If your lawn has plenty of seeding plants like dandelions, the grass you collect from mowing will also have weed seeds. Hot compost the grass waste first, or pull up weed seedlings as they sprout and place them back on the soil to decay.
Straw
Straw is like the dry version of grass clippings. Farmers collect dry grass stalks and pack them into tight bundles that are easy to use. This is a wonderful amendment that keeps the dirt in place while also nourishing it, although it does have some challenges.
As it decays during the winter, it can grow slimy and wet. This isn’t an issue unless you grow onions or garlic crops and their relatives in this garden bed. The straw can invite fungal conditions that threaten your bulbing crops before you can harvest them. Use a different amendment like compost for these plants instead of straw.
Straw adds carbon and nitrogen in healthy doses, making it ideal for any plant, no matter if it’s fleshy or woody. Instead of amending soils with it, you may also mix it in with grass clippings to have the perfect mix for compost. The simplest way to use straw is to scatter it all over bare soil to ensure the ground stays warm and secure throughout the winter.
Sawdust
Sawdust is chock full of carbon! It’s perfect for soils where woody trees and shrubs grow. The sawdust feeds beneficial fungi in the soil, and they help the tree. Another name for these fungi is mycorrhizae—they form underground networks with their mycelia that bring nutrients to tree roots in exchange for sugar.
Sawdust pulls in some nitrogen as it initially decays, which may cause lower yields for leafy crops. Apply it to your vegetable beds in the fall to prepare for planting in spring. It’ll suck up nitrogen in the off-season, then decay into carbon-rich humus for your crops as the weather warms.
Before adding sawdust outdoors, ensure it’s chemical and treatment-free. Some chemicals persist in the environment for a while and can negatively affect plants and animals. Apply chemical-free sawdust wherever woody shrubs, trees, and perennials grow to benefit them and the fungi hiding belowground.
Biochar
Biochar does wonders for garden soil! It provides air holes so plant roots can breathe and hosts fungi inside its wooden pockets. Make it by heating wood to a high temperature where it smolders but doesn’t burn. The heat creates charcoal chunks that you can use directly in your garden.
Biochar also sequesters carbon! Instead of carbon dioxide burning off of the wood and entering the air, it stays in the biochar. As it decays, soil organisms incorporate the carbon into the soil where it remains. Use biochar to boost your garden and to help global ecosystems gain more resilience towards climate change.
Find biochar online from reputable sources, or make your own when you have a fire! Burn chemical-free wood and remove the large, black, charred chunks after the fire. Chop these biochar chunks up into little pieces, and mix them in garden soil. They’ll decay throughout the winter and provide air pockets for water, nutrients, and air belowground.
Coconut Coir
Coconut coir is a waste product of coconut processing. It’s coconut fibers that remain after processors extract the meat and juice. Chop up the fibers and you have coco coir! It makes an excellent soil amendment, works great in potting mixes for container plants, and is the perfect base for vermicomposting systems.
Coco coir also works well as a growing medium for hydroponic systems. Because it’s “soilless” it won’t invite pests, diseases, or fungal growth. Pure coir lacks decaying organic material and will stay tough and fibrous, unlike a readily decaying medium like compost.
You may use coco coir in outdoor soil mixes too if you’d like! It will decay, it just needs other materials near it to facilitate a quicker breakdown. Mix broken-up coir with compost, fall leaves, or grass clippings to boost these improvements’ drainage, absorbency, and carbon levels while they break down.
Organic Fertilizer
Fall is a good time to add fertilizer for next year’s crops. It’ll decay over the cold months, and provide a fertile boost to fleshy crops as the weather warms. Mix some into compost before applying, or add it directly on top of the soil. You don’t have to mix it in that well since you won’t be planting for a few months. Simply broadcast it in an even layer on the soil’s surface.
The only time you don’t want to add organic fertilizer during autumn is if you have woody shrubs or trees growing in your garden. Fertilizer will trick them into growing tender shoots susceptible to frost damage. If a plant goes dormant during the winter, it doesn’t need nutrients until it starts growing again.
Some crops benefit from a fall fertilizer boost. Autumn is an ideal time to fertilize lawns, beds with bulbs, and early blooming flowers like hellebores, violas, and pansies. Use a soil testing kit first to see if your garden needs nutrients before adding them. Some soils have all the necessary components in them and don’t need improving!
Azomite
Organic fertilizers typically contain lots of nitrogen, phosphorous, and calcium, but they often lack important trace minerals that plants need in low doses. These nutrients can decline in gardens as trees, shrubs, and annuals pull them up to use during the growing season. Add a nutrient booster like azomite to replenish them.
What is azomite? It’s a mineral that naturally occurs in parts of Utah. Miners pull it out of the earth and grind it into an easy-to-use garden improvement. Soils low in magnesium, calcium, and iron will benefit from a yearly dose of this mineral.
Find azomite online or look for it at local garden centers near you. Use the package’s instructions to determine the correct dosage for your yard. Azomite benefits potting mixes, raised beds, and in-ground soil. Apply it in autumn to benefit species that sprout next year.
Garden Lime
Fall is an ideal time to consider shifting soil pH levels. Maybe you want to grow blueberries and have alkaline soil, or you have acidic dirt and want to grow vegetables. No matter your needs, simple garden amendments exist that influence pH throughout fall and winter for easy planting in spring.
Garden lime works to raise pH levels, creating more alkaline soil where you add it. If the soil is acidic, it’ll make it neutral, and when the soil’s neutral it’ll make it more alkaline. Apply it in fall to lawns to prevent moss growth, on acidic vegetable beds, and near fruit trees. Lime also supplies calcium to plant roots, preventing blossom end rot where peppers, tomatoes, and eggplants grow.
Garden lime doesn’t work efficiently where calcium is already present at high levels. Too much calcium prevents plants from sucking in magnesium, which they need to grow leaves, flowers, and fruit. Use the recommended dosage on the lime’s packaging to ensure you shift the pH to a level that’s not too extreme.
Garden Sulfur
Garden sulfur works opposite to garden lime—it lowers pH levels, creating neutral or acidic soil. Sulfur works slowly, which is why autumn is an ideal time to apply it. Mix it into the soil without having to worry about damaging sensitive annual plants’ roots. The more you incorporate it, the quicker it will work.
Plants that commonly need sulfur are Vaccinium species, hydrangeas, rhododendrons, azaleas, and evergreen trees. If you have plenty of these species on your property, consider testing their soil and adding the sulfur they need. A proper pH allows plants to thwart pests, diseases, and extreme weather conditions.