11 Amendments to Add to Your Soil in September for a Healthy Garden

September is a great time to rebuild your soil for next year's growing season by adding amendments. There are many ways to do it! Join gardening expert Melissa Strauss to discuss some great ways to amend for a healthy garden.

Close-up of a metal hoe evenly spreading dark amendments over the topsoil of a wooden raised garden bed.

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September 22nd marks the end of summer, bringing the magic of autumn. It’s prime time for starting your cool-weather crops. Or, if you have depleted soil from summer’s heavy feeders, it’s time to work on amending your soil to replenish what’s been lost. 

There are several reasons to choose September to improve your soil’s health. For one thing, the earth is warm and easier to work with. Come early spring, you must contend with hard, thawing soil, which can be a bear to work amendments into. Right now, you likely have plenty of residues or leftover plant material that you can work into the soil to add nutrients as they decompose. They take time to break down, and winter is a great time to allow this to happen. 

Another reason to add certain organic material in the fall is to give it time to mellow. That way, it will not burn your new spring roots. Amending soil in the fall is a good idea, as well, for your existing plants. Fertilizing during the hot summer months can be risky, as the plants are already experiencing stress. The cool autumn weather alleviates that stress, so the fertilizer doesn’t burn up roots in drier soil

Moreover, doing these tasks now—while the weather is cool and beautiful—saves time in the spring. Once it’s done, it’s done, and you can skip this process and get right to planting when the ground thaws. 

Let’s examine some great ways to amend your soil. These materials will feed the earth over the winter, restoring health and fertility. 

Compost

Close up of gardener's hands in yellow gloves holding compost over green compost bin.
Composting recycles waste into nutrient-rich material for your garden.

If you’re not yet familiar with composting, it’s a habit that any gardener can benefit from. Composting is recycling organic materials to create an earth-like material full of nutrients that feed your plants. 

Compost is a free fertilizer made from kitchen and garden waste. It provides an environment for insects, fungi, bacteria, and other helpful organisms to break down the materials we dispose of. Compost also helps loosen compacted or clay soil, making it more hospitable to root growth. 

September is a great time to amend soil with compost. Top-dressing your beds with compost in the fall allows them to mature and become a useful source of plant nutrients. Over the winter, rain, and snow send these nutrients down into the earth. 

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How to Do It

Remove lingering weeds or grass from empty garden beds. Spread a three—to four-inch layer of compost over the existing earth. You can also add a layer of compost around the base of established perennials. This natural fertilizer will await them when they re-enter a growth phase after winter dormancy. 

Worm Castings

Close-up of a gardener's hands in yellow gloves holding a handful of dark soil mixed with red wiggler worms.
Vermicast enriches plants with essential nutrients and growth hormones.

Worm castings are another great amendment for your September soil. If you’re unfamiliar: worm castings, or vermicast, is precisely what it sounds like. It’s what worms leave behind as they process organic matter as food. 

Vermicast contains the most common fertilizer nutrients: nitrogen, phosphorus, and potassium. It also contains natural growth hormones, beneficial bacteria and microbes, calcium, and sulfur. In short, it’s valuable stuff for feeding plants. 

Now, I’m not a worm person myself, but my Sister-in-Love is, and she has graced me with some of her black gold. I will tell you this: those were the healthiest pansies I’ve ever grown. 

How to Do It

There are several ways to acquire worm castings. The best way is to befriend a worm farmer who likes to share. Without such a companion, there are other simple and complex avenues

You can certainly take up the hobby of vermiculture, that is, the intentional cultivation of worms for compost. It’s easy enough to get started with a worm composting kit, but a moderate investment of time and money is involved. It’s well worth the price tag if you love the stuff. 

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However, if you don’t want to do the dirty work yourself, you can order worm castings here. Epic has done the heavy lifting, and we are happy to share the finished products.

You can top-dress your beds with worm castings like you would compost or other types of manure. Over the winter, the nutrients will seep down into the soil and rejuvenate them.

Another way to use worm castings is as a side dressing. You can sprinkle a bit in when digging a hole before placing the root ball for planting at any time of year.

Leaf Litter

Close-up of decaying brown fall leaves, with curled edges and dark, soggy patches.
Decomposed leaf mulch regulates moisture and temperature, and enriches garden beds.

Did you know that you can make your own mulch from the leaves that fall from your trees in the fall? Reuse your leaves to replenish your garden beds rather than bagging them and leaving them by the curb. 

Leaf mulch does a great job of regulating the temperature and moisture levels in your garden beds. It prevents erosion of bare soil by rain and wind. It also breaks down into nutrient-rich leaf mold, which feeds your plants over time. 

The slower release of nutrients from organic matter is great for the garden. Although you may still want to fertilize occasionally, naturally rich soil is the best way to grow strong, healthy plants. 

How to Do It

Depending on how much work you want to do now, you can do this in one of two ways. You can gather leaves and compost them by layering brown leaves with green clippings and allowing them to break down over the winter. 

You can also apply the leaves directly to your beds to decompose directly into the ground. My husband really appreciates being able to skip bagging the leaves and making me happy by using them to feed my garden. 

We find it easiest to use a leaf blower, blowing the leaves into piles directly on top of beds. You can rake them if you prefer, or you can shred them to expedite the decomposition process. 

Manure

Chickens scratching through a large pile of manure, spreading it with their claws in a farmyard.
Using composted manure in fall enriches garden beds over time.

Here we go again, discussing number two and how great it is for your garden. If you’re a chicken mama, like me, I have some news that might have you out cleaning the chicken coop to gather manure in a jiffy. 

Manure typically refers to excrement from cattle, horses, or chickens. Decomposed livestock manure is a great nitrogen, phosphorus, and potassium source. Manure is only safe for use in beds where you grow edibles once it has been composted. 

The benefit of using manure in the fall garden is that the nitrogen in manure takes time to break down. It won’t be useful to plants until it does, and using it in the fall solves this problem. 

How to Do It

Now, about those chickens, making your own composted manure is a bit more complicated than purchasing it. You have to ensure it gets heated to at least 131°F (55°C) to kill harmful pathogens like E. coli and salmonella

If you are going to age and compost your manure for use in beds with edibles, do so intentionally. It takes some time, and you want to eliminate all harmful pathogens. Purchasing already composted manure is safer if you’re not sure.

Manure, like compost or worm castings, makes an excellent top dressing for your beds. That is if you simply want to drive those nutrients into the earth. Mixing it in is better if your objective is to improve the texture and moisture capacity

If you want to take the faster path, go ahead and top dress. Since there is plenty of time for the nutrients to work their way into the earth over winter, this works just fine. Wait until the earth is about 50°F (10°C) to slow decomposition. 

Bat Guano

A bat with outstretched wings gliding through a dense forest under the evening sky.
Bats offer a nutrient-rich fertilizer and control mosquito populations.

Another animal that produces valuable fertilizer is the humble bat. Bat guano, or excrement, is an excellent, slow-release fertilizer that feeds your plants over an extended period. 

A great characteristic of bat guano is that when applied correctly, it won’t burn up your plants. It has very little smell compared with other types of manure. It’s also rich in nutrients that are readily available to your plants. 

How you acquire your bat droppings can be controversial. Some issues have come to the forefront about the ethics of harvesting it. Also, dried guano is not good to inhale, so working with it is more complicated. 

How to Do It

We recommend incorporating a bat house into your garden or yard. This will naturally draw bats to your yard. Bats are incredibly helpful animals despite the somewhat creepy reputation they get. 

Bats eat a lot of mosquitos, which can carry diseases that are harmful to humans. That alone was enough for me to want to install a bat house

If you can attract bats to your garden with a bat house, you can collect their droppings via a small saucer placed on the ground below the house and apply them directly to your beds. You won’t need much, and it’s effective stuff. Top dressing works, and so does mixing it in.

Peat Moss

A close-up of a gardener's hand wearing a blue glove, holding a handful of dark brown peat moss.
Freshwater plant material lowers pH, aerates soil, and retains moisture.

If you’re a Scotch whisky drinker, you surely know how useful this next garden amendment can be. This type of freshwater bog plant also has a wonderful effect on the garden. 

Peat moss is the bottom layer of the plant that has partially decomposed. It’s great for lowering the pH in your soil for acid-loving plants. It also aerates the soil and helps dry types retain moisture. 

The use of peat moss in gardening is not without controversy. Overharvesting harms the environment by damaging the biodiversity in its native range. It takes a long time to break down, so a single application will last several years and contribute to loosening compacted soil.

Alternatives include coconut coir, but that has its own sustainability downfalls. Ultimately, the choice is yours. Peat moss is fast-growing, and sustainable harvesting methods exist, so check out your source before purchasing. 

How to Do It

Soak your peat moss in water for a few minutes before using it. You can top-dress plants with it and allow it to work its way naturally into the earth. 

Mixing this one in with the dirt can be more effective, and fall is a good time to do so. Remember that soil is easier to work with in the fall. 

Mulch

Close-up of young lettuce plants growing in rosettes among soil mulched with dry straw.
Applying mulch in fall reduces weeds and improves soil.

When applied in the fall, mulch does some great things in the garden. For one thing, it significantly reduces weeds. It also insulates the soil, tempering temperature fluctuations and helping it to hold moisture.

Over time, mulch breaks down and incorporates into the earth. It improves drainage and structure, and organic mulch adds important nutrients as it decomposes. If you add some each year, you will create more high-quality soil.

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How to Do It

Mulching is a cinch. Weed the area before you put it down so you have a fresh canvas underneath. Lay down a two- to three-inch layer of organic mulch and let it do its job!

Alfalfa Meal

Small, rectangular pallets of alfalfa meal with a greenish-brown color and a coarse, granular texture.
Natural fertilizer enhances gardens with essential nutrients and vitamins.

High-quality alfalfa meal is an excellent natural fertilizer. It improves the soil’s condition and nutrient composition

You can use unprocessed alfalfa in your beds as a type of mulch, which will help suppress weeds. However, if you want to get those valuable nutrients into the earth now, an alfalfa meal is the way to go. 

Alfalfa contains significant amounts of nitrogen, phosphorus, and potassium. Its benefits don’t end there, though. It also contains iron, magnesium, and vitamins A, B, and E. Add a heap of amino acids to that, and you have garden gold. 

How to Do It

If you want to keep it simple, you can mix the meal directly into your beds. About five pounds per cubic yard is plenty. 

If you want to take it further, you can soak your alfalfa in water for about 6-12 hours. Then, use the resulting liquid, often called tea, as a drench. Pour some around your shrubs while you’re at it.

Gypsum

A hand holding a small piece of gypsum with a light gray color and a slightly rough, crystalline texture.
Calcium and sulfur enhance structure and prevent erosion.

Gypsum might not be the first mineral you consider when deciding how to amend your soil. However, this mineral has some beneficial agricultural uses that might pique your interest. 

Gypsum contains significant amounts of sulfur and calcium. It contains calcium sulfate, which doesn’t alter the soil’s pH as much as calcium carbonate. This calcium can travel farther down into the earth, encouraging deeper roots. 

It can also affect the composition of your soil. Gypsum improves aeration and increases the soil’s water-retaining ability. Additionally, it helps to prevent erosion. Another great effect gypsum has on the earth is that it can reverse excess salts left behind by commercial fertilizers. That is great for your plant’s roots. 

How to Do It

September is the right time to apply gypsum amendments to your soil because of increased rainfall. The additional moisture from rainfall and the slower evaporation are important factors. 

Try to distribute the ground gypsum evenly over your beds. Sprinkle rather than dumping and redistributing. You can also mix it with compost or manure and top-dress your beds with the mixture. Water immediately after you apply it.

Cover Crops

Red clover plants with vibrant green leaves and pinkish-purple flower heads, growing in clusters.
Planting green manure crops enriches the ground and boosts biodiversity.

Cover crops are a nice way to keep some green in your beds while replacing valuable nutrients. Cover cropping is the practice of planting things that improve the condition of the soil in between crops that deplete it. 

Some great cover crop plants include clover, alfalfa, and legumes. All of these are nitrogen-fixing plants. This means they draw nitrogen from the air and deposit it into the soil through their roots instead of taking nitrogen from the earth, as most plants do. 

Other benefits of cover cropping include increased biodiversity, reduced erosion, and pest suppression. It also reduces compaction and increases fertility. You can also allow your cover crops to flower so they can feed beneficial insects. Make sure to mow before they self-sow

How to Do It

It’s simple: Sow these seeds in your garden beds in the fall. September is great for cooler climates, but hold off for a month to ensure the weather is cool enough in warmer climates. Most cover crops love cool weather. 

Most of these plants are easy to maintain. Some die off in winter, depending on your climate. In warm climates, many will grow through the winter as they are frost-tolerant. 

Before your crop flowers, simply dig it into the soil. You can also cut it off at ground level, leaving the roots decomposing and feeding the earth. Leave the tops of the plants on the surface to act as mulch. 

Bone Meal

A hand holding a small amount of bone meal, a light beige powder with a granular texture.
Ground bones enrich ground with calcium and essential nutrients.

Finally, bone meal, which comes from ground bones, is good for the garden, too. The bones used are usually bovine but can come from other animals. Bone meal contributes calcium to the earth, which is great for healthy root development. 

It benefits the structure, which also benefits root development. It increases microbes while adding phosphorus and calcium to your beds. It’s great to use in beds where you intend to plant root vegetables or bulbs, and will result in well-developed roots. 

How to Do It

Apply bone meal similarly to the way you would gypsum. You can mix it in with your compost and top dress as usual. You can also sprinkle it evenly over the surface and water or mix it in. Use a garden fork to turn over the earth where plants aren’t already planted.

You can also use bone meal at planting time or when your plants need a boost. Side dress at planting time, or simply sprinkle it on top of the soil around existing plants and water it in. 

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