Do you have soil that’s high in clay or sand? Here are some of my favorite organic soil amendments that can improve conditions for growing vegetables.
This page may contain affiliate links. Please read my disclosure for more info.
Gardeners often complain about having unworkable clay soil or sandy soil in which nothing will grow. We tend to think that our plight is totally unique compared to all of those *lucky* gardeners out there who naturally have perfect soil!
Truth is, the majority of gardeners have challenging soils that require improvement for cultivation. We are all special by not being unique! 🙂
Ideal garden soil will bring these two spectrums into balance. Loamy soil balances clay, sand, and organic matter. Organic soil amendments can help us do this.
Improving Soil Using Soil Amendments
Organic soil amendments can increase beneficial soil organisms, organic matter, and improve moisture retention.
The following list contains a variety of soil amendments from animal, mineral, and plant-based sources. Some items are free and easy to find locally, while you’ll have to purchase others.
In general, add soil amendments in the fall, or in the spring before planting the garden.
I’ve divided soil amendments into three categories: animal-, mineral-, or plant-based amendments.
Animal-Based Soil Amendments
Some animal-derived soil amendments can increase beneficial soil organisms in addition to improving soil structure. Apply untreated animal products nine months before harvest, or at a minimum of two weeks before planting.
Mineral-Based Amendments
Use mineral-derived soil amendments to correct mineral deficiencies. Mineral-based amendments do not break down easily, so they can be over-applied. That’s why it’s essential to get a soil test beforehand so you know what you need.
Plant-Based Amendments
Use plant-based soil amendments to improve soil structure. Because herbicide contamination can result in stunted growth and lackluster performance, it’s important to source herbicide-free amendments. Surprisingly, contamination can occur even if you don’t use herbicide in your garden and purchase organic-approved amendments.
Grow a garden that’s both productive and manageable with my Complete Garden Planning System, which includes practical tools for planning your season from seed to harvest.
Here are a few of my favorite amendments from each category:
1. Bat Guano (Animal-Based Amendment):
Bat guano is a fast-acting, organic fertilizer high in nitrogen and phosphorus, which promotes strong and healthy plant growth. It can also improve the texture of soil, improve drainage in heavy soils, and help to neutralize soil contaminants. By increasing beneficial bacteria in the soil, it helps to protect plants against disease.
Bat guano is highly concentrated, so a little goes a long way. As with other animal manures, mix into the soil in the fall, or at least two weeks before planting. This allows time for the nutrients to break down into a form that plants can absorb.
Note: This soil amendment is considered by many to be unsustainable, due to harvesting methods that may destroy cave habitat and negatively affect the health of bat populations. Although an excellent amendment, I recommend using caution and using many of the alternatives listed here.
2. Manure (Animal-Based Amendment):
Use livestock manure mainly as a slow-release fertilizer. That’s because it contains most of the elements required for plant growth including nitrogen and many other nutrients. It can also condition the soil, increasing beneficial soil organisms and moisture retention.
The manure can come from nearly any livestock animal, NOT dogs or cats. However, it’s often contaminated with herbicide. Read more about contaminated manure and the serious problems it can create.
Spread fresh manure at least 3-4 months before harvesting a crop to avoid potential pathogens. Spread it in the fall or one month before planting. This timing will prevent it from burning plants.
Although aged manure contains less nitrogen than fresh manure, this soil amendment makes an exceptional conditioner.
- Turn manure into the soil within 12 hours of the time of spreading to capture the nitrogen in the soil. This prevents it from leaching away.
- Do not spread fresh manure on ground that’s frozen or oversaturated by a recent rain.
- If heavy rain is in the near forecast, wait it out.
Many state laws include these common agricultural prohibitions, which reduces runoff from farm fields and helps to keep waterways clean. Plus, you don’t want all of your hard work and valuable nutrients to wash away!
Worm compost
3. Worm Compost (Animal-Based Amendment):
Worm castings are the richest fertilizer known to humans, and is high in minerals. This soil amendment is also high in nitrate, a more bioavailable source of nitrogen than that found in commercial fertilizers.
Worm castings help plants regulate water usage, improve soil structure, and increase plant vigor. You can even use worm castings in place of potting soil. There’s no upper limit to how much of this amendment you apply at one time.
Buy bagged worm castings or learn how to create your own worm castings in a worm bin. Be sure to check out these worm bin problems for beginners.
4. Greensand (Mineral-Based Amendment):
Greensand is a slow-release soil conditioner largely composed of glauconite, a mineral harvested from ancient forest floors. It’s considered high in potassium and trace minerals such as iron and magnesium.
The main benefit of this mineral, however, is loosening clay soil and improving moisture retention. Read more about improving clay soil.
Apply this soil amendment in early spring before planting.
Note: Do not confuse greensand with regular sand, which does not have the same benefit.
5. Comfrey (Plant-Based Amendment):
Comfrey is a perennial herb with large green leaves and purple, pink, or white flowers. This soil amendment is used in many ways to fertilize soil.
It can activate a compost pile due to its high nitrogen content. Use the chopped leaves as mulch around fruit trees and mature fruiting vegetable plants.
To use comfrey as a green manure in a vegetable garden, spread chopped leaves in the fall. Then gently incorporate them into the soil using a digging fork in the spring before planting.
My favorite variety is Russian comfrey because it doesn’t spread like true comfrey can. Learn more about growing comfrey to get the most out of this useful, biomass-producing plant.
Comfrey powder is a great way to fertilize a garden bed in the spring before planting. Learn more about the many uses of comfrey in the permaculture garden, including how to make comfrey powder.
6. Compost (Plant-Based Amendment):
Homemade compost made from food scraps and yard waste is an inexpensive, slow-release fertilizer and soil conditioner for the garden. It’s also a great way to keep household waste out of the waste stream.
However, it’s important to know how to keep persistent herbicides out of your compost bin, even if you don’t use herbicide in your garden.
As a matter of fact, herbicides can even contaminate commercially made soils that are approved for Organic agriculture! Learn 5 essential questions to ask a producer before buying compost soil for your garden.
Got a compost pile that’s slow to break down? This happens when there’s not enough nitrogen, or green matter, which is common in backyard compost systems. Get your compost heating up with this organic-certified compost accelerator.
Homemade compost improves soil structure by aerating, improving drainage, and retaining moisture retention. Add 3-4 inches of this soil amendment each spring before planting and work it in with a digging fork.
For perennials, spread compost annually around trees and shrubs without working it into the soil.
Read more about 6 ways to build a compost bin.
Would you like to learn more about using natural amendments to improve the quality of your soil, reduce maintenance, and increase yield?
You’ll find loads of information just like this in my award-winning book, The Suburban Micro-Farm.
7. Cover Crops (Plant-Based Amendment):
Cover crops increase soil fertility, improve soil texture, and increase beneficial soil organisms and fungi. All of these benefits together can help to reduce pests and disease. Sow this “soil amendment” in garden beds in the fall, about four weeks before the frost date.
Overwintered, by springtime cover crops are full and lush, outcompeting early spring weeds. When they begin to flower or set seed heads, cut them back just above the soil line. After a couple of days, incorporate the “green manure” into the soil with a digging fork, breaking up roots.
Many micro-farmers use livestock such as chickens to help turn cover crop residue into the soil.
Wait three weeks before planting in the bed.
There are many kinds of cover crops. The mixture that’s right for you will depend on your local climate and your goals. If your garden is a no-till garden, avoid grass-type cover crops since they will be a challenge to hand-turn into the soil.
Your local extension office can help you choose appropriately. Try clay-busting plants!
When cover cropping, alternate keeping a few garden beds for overwinter vegetable production, while planting the rest in cover crops.
Leaf mold
8. Leaf Mold (Plant-Based Amendment):
This soil amendment is effective as a water-retaining mulch or soil conditioner. In fact, “Pound for pound, the leaves of most trees contain twice as many minerals as manure.” Fall leaves are both a valuable mulch and soil builder.
Leaf mold is simply leaf mulch that has aged for two to three years. It can benefit the garden in many ways. The consistency of leaf mold lies somewhere between shredded leaves and leaves that have composted completely into humus.
When hot weather strikes, lay leaf mold over the garden as mulch, keeping it away from the stems of plants. It has a cooling effect on soil. As the mulch breaks down, it will attract beneficial soil organisms while transforming into humus.
To make leaf mold, shred the leaves first by running over them with a lawnmower, or by using a leaf mulcher.
To make “quick” leaf mold, make a rectangular pile of shredded leaves, 5 feet square by 5 feet high. Turn the pile monthly, and you might be able to make leaf mold in as little as 12 months, though the process usually takes a couple of years.
As a soil conditioner, add finished leaf mold to garden soil in the fall, then mix it in with a digging fork in the spring before planting.
9. Wood Chips (Plant-Based Amendment):
With the growing popularity of the film Back to Eden, gardeners are adding wood chips at an accelerated rate. However, it’s important to know how to use this soil amendment correctly.
Adding wood chips is like mimicking the forest floor, where leaves and twigs naturally decompose on top of the soil. Wood chips increase organic matter, improve nutrient levels, and increase the numbers of beneficial soil organisms as they break down.
They hold in moisture, reducing irrigation needs. Covering the ground, they reduce weeds. Wood chips create a stable growing environment by insulating against the hot summer sun and freezing winters.
Use wood chips as mulch rather than tilling or mixing them into the soil.
To use wood chips in the vegetable or perennial garden, age them for two or three years before mixing them into garden soil as an amendment, and add a teensy amount of blood meal with them to make up for lower nitrogen availability.
Or lay fresh wood chips on top of the soil as mulch without mixing them in.
I prefer to use wood chips in the pathways of my vegetable garden. That’s because beneficial soil organisms and fungi will enjoy plowing through my beds between the pathways.
Tree trimmers often deliver wood chips for free. For example, I have access to an arborist who delivers a trailer-load for a $20 fee.
Summary
Focus on increasing soil life and soil structure to help your growing conditions. First, focus on those soil amendments that you can make for free. They will often have the biggest impact because they will jumpstart biological activity.
Later, if you choose to add a store-bought amendment, such as greensand, you can purchase less of it. This will maximize the efficiency of your efforts and reduce your micro-farming costs, too.
Resources:
- Soil Biology Primer by Elaine Ingham
- Teaming with Microbes by Jeff Lowenfels
- The Suburban Micro-Farm: Modern Solutions for Busy People by Amy Stross (shameless plug!)
Whether your challenge is sandy or clayey soil, these amendments will help improve your gardening success.
What type of soil do you deal with? What soil amendments have helped improve it?
READ NEXT:
- How to Keep Herbicides out of your Compost Bin
- How to Prevent Soil Erosion in Gardens and on Farms
- Mulching in the Permaculture Garden
>>> Get my free 19-page Guide to Organic Soil Amendments for more ideas:
Nicole Schauder says
Hi Amy!
Where do you get your bat guano? Is that available somewhere (hopefully free?)
Thanks and good luck with remodeling!
Amy says
I don’t often purchase bat guano b/c I like to focus on the free amendments first, but I trust FoxFarm products. I usually buy it from a local gardening store, but you can also buy it on Amazon.
Christoph Day says
Create a bat habitat, We have a small version of a Black forest house roof shape covered with Nipa palm leaves. The Bats are hanging under the roof tip and let their poo and leftovers fall down infront our house. Sometimes ants come and brake these organic bat poo and leftovers of there food into fine dark compost. The bats we have are fruit bats and there are many seeds mostly of bananas and wild figs but also seeds of trees which we don’t know yet, in their excrements. The bats chew their food, swallow the so extracted juice and spit out the solids. On this way they stay lighter when flying. They often bring their food like Guavas, Lanzones, wild Bananas (wild Abaca) and wild figs to their habitat below our roof and eat there. Bill Mollison suggests in his “Permaculture – A Designers’ Manual” to put roofs inbetween or inside trees as Bat habitat. The roof should be close all around and the bats go in from below the roof so they have the most protection. Dom shaped, Pyramidial shaped or like the roof of an ordinary house with the triangle sides closed are thinkable. The bat guano so I believe is different: The bats living in caves are maybe not the fruit bats and the caves in which bats are living are very stinky (Ammonia, wewe mixed with poo). Freiends accompanied me to such caves. I however followed them only once inside the cave. Its ceiling is full of bats and the ground full of the excrements of the bats. then, if you have to climb up the rocks your hands get covered with those excrements. And inhealing the strong ammonia isn’t quite healthy. Those cave bats might eat insects.
Back to the bats under our house. The Bat excrements turn into a nice compost. The seeds within it are still viable and if you use it, they will grow. By using it for starting cucurbitaceae it’s OK. the growing wild bananas make for a green groundcover which can be delt with. When the ants go over the Bat excrements they break down the seeds. They leave a layer of fine compost which I sometimes collect. I want to use it for starting tiny seeds. So I differ between Bat compost and Bat-Ant compost.
Leslie says
I would really be cautious about manure from cows and horses. I say that after being a horseman all my life and using the manure. But now a lot of ranchers, farmers use a herbicide called Milestone to kill board leaf weeds, thistles. The hay cut itself or the manure after the horse or cow eats the hay, pasture persists in the manure or hay…it WILL kill your plants. Yes they will start out but then the leaves curl, and plants is majorly stunted or dies. This happens on tomatoes, beans and others. It has happened to me more than once in Lander WY. Ask the rancher/ farmer if they spray their fields…answer , well yes we have to get rid of the thistles… Look else where.
Leslie
Amy says
It’s sad that we have to worry about herbicide in the manure, but it’s the reality today. I’ve certainly had to deal with the negative effects of herbicide in my garden before I knew to ask questions first about spraying.
George Griffin says
I have a large backyard garden with heavy clay soil. I used gypsum when I first started the garden, but use horse manure exclusively now. It makes the clay workable, allows percolation of water and breathing of the soil. I’ve found that it’s a mild enough source of nitrogen that seedlings can be planted directly in it. I’ve had no problems with it at all. I’ve used fresh manure, green and moist, dried and aged and fully composted. Each type has served well. Given a choice I would use aged and composted and then barely turn it into the soil.
Your article shows the many options that are available. Take a look around and see what you can find in your area. Thanks for the article.
Amy says
It’s all about what the horse ate — an important question to ask the horse owner or caretaker.
Cheryl Ann says
Amy, I have 4 horses myself and I do use their manure in my garden. Just be aware, however, that horses are WORMED at least 3 or 4x a year. Ugh. Don’t really want that manure in my garden! I do have my own compost pile, however, so at least I know what goes into that.
Amy says
This is a great reminder, Cheryl. How do you minimize the exposure to this medicine? Do you simply avoid the manure directly after worming, or…are there any natural worming solutions that would make the manure more organic?
This gets me thinking about livestock in general, and which typically take prescription wormers and which don’t.
Stephanie Merrill says
Silver Lining Herbs sells a natural herbal worming product so you can avoid poisoning your horses as well as the soil.
James Tomell says
I have used horse manure from a polo club for years as bedding for my vermiculite beds. Those horses get wormed frequently, but the residual dewormer in the manure quickly breaks down during the thermophilic composting process. I have never had a problem with dewormers. My worms thrive in the horse manure bedding.
Roger says
Hello, and thank you for a well written article. Lots of great information to unpack. I would like suggest an additional item for your list: coffee grounds too lend plenty of nutrients. Phosphorus, potassium, magnesium and copper, in addition many garden plants like strawberries and blueberries will benefit from the boost of acidity. Best of all coffee grounds are a plentiful and easily obtainable resource, just go sweet talk your local coffee shop baristas into giving you their discarded grounds!
Amy says
I love coffee grounds and do enjoy their benefits in my garden. And I also collect them from a local coffee shop. I agree, they have a lot to offer. 🙂 I didn’t include them in this list because they are quite acidic and can affect soil pH, therefore, they aren’t appropriate for all soils. The amendments in this list are appropriate for all soil types (to my knowledge).
James Tomell says
I compost 50 MT of coffee grounds weekly mixed with coarse sawdust, coconut coir, biochar, hog, chicken or water buffalo manure, mixed vegetable scraps and fresh weeds. Resulting acidity is not a problem. I also use the fresh compost as vermiculite bedding.
Starbucks corporate policy is to give used coffee grounds to anyone that asks for them, first come, first served. I started my first vermibeds with coffee grounds from Starbucks.
Nita Fair says
Can you please tell me what type of wood chips are suitable for the garden? The only ones I would have access to in any amounts are spruce and poplar.
Amy says
It depends on how you intend to use the wood chips. In pathways? I’d use any wood chips available. As a mulch under perennials? Any will do in my opinion. If you intend to age them as I’ve instructed above to use as a soil amendment, I’d guess that the spruce would be acidifying, which could be good or bad depending on where your soil falls on the pH spectrum.
Betsy says
Homemade compost is the best. I put yard waste as long as it is not diseased or covered with seeds and kitchen scraps except for meat in my compost which has attached lots of worms.
Karen M says
I am newish to gardening, and my first year attempting to plant a garden, a friend came over and said “I think you need about 40 bags of manure in your garden”. So, I did that! A guy came over and rototilled it into my pretty much clay-based Phoenix, AZ soil. I had an incredible garden that year! I was giving away bouquets of kale! Near the end of my growing season, I had a friend who does woodwork offer to give me all the sawdust I wanted. I thought this would be great to compost into my soil. We sprinkled some of the sawdust right onto the garden, and also put a bunch of it in our composter along with food scraps. We dug it all in, (The second year of gardening, my dear husband hand turned everything. No rototiller option. He formed straight rows, and we amended the rows with the soil in the garden, miracle grow garden soil, and our own compost made from those big plastic tumblers.) But! That next year when I planted my seeds, I got nothing. NOTHING! The only things that grew were volunteers from the first year’s lettuces, etc., that had gone to seed. And weeds. The following year, same thing: Hubby dug it up, used native soil, Miracle gro garden soil and our compost. I planted new seeds, and no plants sprouted. I mentioned this to another friend who suggested that if any of the sawdust my woodworker friend gave me had been from hardwoods, like walnut, that the extra tannins in the wood may have sterilized my garden!!!! Does anyone have any information on this? Is it possible that I happened to buy bad seeds TWO years in a row? (Probably from Home D or Lowe’s.) By the way, weeds still grow very well, so that makes me think that all is not lost, but it was so disappointing to go through all that effort and get nothing growing. Seriously, not a single shoot of spinach, lettuce, carrots, beets… Nothing! Does anyone have any idea about what I can do? BTW, we use drip watering system.
cade says
Eek, sorry for that happening. I would personally try to remove what I can, add it to the compost, and make a seperate, clean compost and build a new clean top layer. Its going to be like starting over for a while but whatever is in that would will break down, whether it is treated or walnut or whatever. I would consider testing the soil ph. adding nitrogen like worm castings or coffee grounds, or even the manue but this can burn your plant seedlings and it’s very heavy for seeds. Seedlings like a very very light soil. The soils drains well when it’s light though so keeping moist can be a challenge. Another thing you can do is either use a seed starting mix or make your own, and grow plants to transplant or usea hand full per seed in the soil
Mikes says
I’ve been mulching my gardens with yard clippings and waste food for years. I only let it compost about half way and throw it around my bananas, pineapples, figs and mulberries. Even though everyone says to let things fully compost I have had really good luck. In fact every year there are several tomatoe plants that grow out of the mulch. Here in central Florida people have a hard time growing them but I have great luck. It’s now I. The 90s and rainy and I’m still getting production. I also have a banana ring and put clippings and garden waste right in. Seems more natural and my bananas are taller and earlier than neighbors who plant in traditional fashion. My only problem I’d i can’t seem to make enough mulch lol
Denise says
Hi Amy,
What is bad about cat or dog manure? I have cats and need to put their poo from the litter box somewhere in the yard, other than what they bury themselves which I have no control over. Is it possible to use around fruit trees and bury it shallow so it can break down (aerobic) which is what they do naturally anyway. I feed good quality cat food and they are healthy. I’ve heard about people using humanure too so it can’t be that the micro-orgaisms are not bio-degradable.
Amy says
Do your research. There are many reasons why dog and cat poop isn’t used as fertilizer in the garden, including parasites and harmful pathogens. They aren’t vegetarian livestock. Sure, there are ways to compost it, but it isn’t safe for the garden.