When you started your garden, you probably remember the buckets and buckets of compost or soil that was moved into your beds. Or maybe you went the hugelkultur route with some logs and fallen leaves. Access to manure? Throw it in! Sure, why not. Whatever approach you took to developing the garden soil you have today - you may be missing out on this ongoing garden care task: amending the soil. 

Why Amend the Soil?

Over time, after seasons of growing, nutrients are leached from the soil. Rain can wash away nitrogen, plants take up nutrients and don’t return them on their own, and through all this, you can see your crops, over the years, producing less or not as well as they once did. While we as gardeners take from the soil, it’s important for us to also give back, not only for the health of the long term soil, but for the health and production of the overall garden! 

Types of Amendments

Soil amendments fall into three broad categories: fertilizers, soil conditioners, and biostimulants. Certain additives can also fall under multiple of these umbrellas. Each of these act differently on soil and crops and improve your soil in different ways. 

What is a Fertilizer? 

Fertilizers provide one or more of the major plant nutrients - nitrogen, phosphorus, and potassium. The three numbers on amendment packaging (written 0-0-0) indicate the NPK ratio, or the percentage of nitrogen, phosphate, and soluble potassium respectively.

What is a Soil Conditioner?

Soil conditioners improve soil texture and nutrient, water, and oxygen holding capacity. They may also work to change the pH level in the soil. These come in handy when you have especially heavy clay soil or soil lacking organic matter. 

What is a Biostimulant?

Biostimulants include a wide range of ingredients that all help in some way to encourage healthy microbial activity. They work to stimulate natural processes of plants that benefit nutrient uptake and nutrient efficiency, and increase tolerance to stressors. 

Applying Amendments in the Garden

Fertilizers

Vegetable Garden Mix 4-4-4

This balanced fertilizer is perfect for your vegetable garden. It’ll keep steady the transition from vibrant leafy greens to big, red tomatoes all season long. This fertilizer’s mix of fish bone meal, alfalfa meal, feather meal, langbeinite, basalt, potassium sulfate, dolomite, and kelp meal create a broad nutrient profile that’s perfect for all of your edible crops. 

When applying to transplants, add one to two tablespoons per hole and mix into the soil. To feed established plants, side dress with two to four ounces depending on plant size and desired growth rate each month. 

All Purpose 4-6-2

This all purpose fertilizer is a great additive to all kinds of transplants. It’s gentle, and won’t burn sensitive, young plants with too much nitrogen. Over time, it can also enhance soil fertility and microbial activity. This mix of fish bone meal, blood meal, feather meal, alfalfa meal, rock phosphate, langbeinite, humates, and kelp meal is perfect for all your vegetables, flowers, herbs, fruit trees, and more. 

Apply two and a half to five pounds per 100 square feet of garden soil and thoroughly mix into the top three inches of soil. For new transplants, apply one to two tablespoons per hole. 

Vegan Mix 3-2-2

Especially for you vegan gardeners! No animal products involved. This slow release concoction will nourish your vegetables, herbs, and flowers throughout the growing season. This mix of soybean meal, neem seed meal, alfalfa meal, rock phosphate, langbeinite, greensand, and kelp meal will gently and over time improve soil fertility and tilth in combination with high quality compost. 

Apply two and a half to five pounds per 100 square feet of garden soil and thoroughly mix into the top three inches of soil. For new transplants, apply one to two tablespoons per hole. 

Fish Bone Meal 4-12-0

You may recognize this amazing amendment from the other ingredient lists but as a single use amendment, it certainly works its magic. Fish bone meal is an excellent source of phosphorus and calcium which help to support healthy root, bloom, and fruit development. Calcium in particular is helpful if you have an issue with blossom end rot in your garden - this may be the solution you need! 

Apply two and a half to five pounds per 100 square feet of garden soil and thoroughly mix into the top three inches of soil. For new transplants, apply one to two tablespoons per hole. 

Alfalfa Meal 2-0-1

This plant-derived all purpose fertilizer increases organic matter in the soil, encourages beneficial microbes and earthworms, and works especially well for flowering plants. Alfalfa meal can also be used as a compost pile stimulant as it decomposes rapidly and creates heat which helps the rest of your compost to decompose, making more nutrients available to your plants. 

Apply five to ten pounds per 100 square feet of garden soil and thoroughly mix into the top three inches of soil. For new transplants, apply one to two tablespoons per hole. 

Soil Conditioners 

Kelp Meal 1-0.1-2

An excellent source of potash, kelp meal also feeds and stimulates the necessary microorganisms in your soil which improve the overall breakdown of organic material and improves both soil texture and quality. It’s perfect for an early spring or fall pre-planting application. 

Apply one to two pounds per 100 square feet of garden soil and thoroughly mix into the top three inches of soil. For new transplants, apply one to two teaspoons per hole. 

Biostimulants

Worm Castings

This amazing ingredient actually could fall into all three amendment categories. Worm castings are, in the simplest terms, worm poop. Yum! This odorless amendment is a product of nature and can do really amazing things for your garden. Worm castings improve the physical structure, chemical composition, and biological activity of soils making them better and healthier over time and proving itself as a great bio-stimulant. 

Special Use Amendments 

Rose and Flower Mix 4-8-4

Use our Rose and Flower Mix for all of your perennial blooms. This mix provides a great source of nitrogen and a boost of phosphorus for rigorous bud development. This mix of fish bone meal, blood meal, langbeinite, alfalfa meal, seabird guano, rock phosphate, and kelp meal is great for a monthly application for establishing perennials and an annual application for established perennials around your last frost.

Apply two and a half to five pounds per 100 square feet of garden soil and thoroughly mix into the top three inches of soil. For new transplants, apply one to two tablespoons per hole. 

Acid Mix 4-3-6

What do you grow that loves acidic soils? Blueberries, raspberries, rhododendron, azaleas, hydrangeas, and other evergreen plants all come to mind! Got these in your garden? This is the mix for you. This mix of cottonseed meal, fish bone meal, langbeinite, rock phosphate, and kelp meal will keep those acid loving perennials happy and healthy! The addition of cottonseed meal in this mix can lower the pH of your soil over time.

Apply two and a half to five pounds per 100 square feet of garden soil and thoroughly mix into the top three inches of soil. For new plants between one and two years old, apply a half cup into the large hole and mix with the backfill soil. 

Blood Meal 12-0-0

Blood meal is a readily available source of nitrogen for your heavy-feeding plants. Can be used liberally on all leafy greens and is great for corn and tomatoes, especially if your soil is depleted. Too much nitrogen can cause a plant to produce a lot of (really beautiful and healthy) foliage but you may see a lack of blooms or fruits. Apply to heavy feeders alongside balanced fertilizers when producing blooms and fruits. 

Apply two to three pounds per 100 square feet of garden soil and thoroughly mix into the top three inches of soil. For new transplants, apply one teaspoon per hole. 

Looking for more information on specific soil amendment ingredients? Check out our ultimate Cheat Sheet! 

	Article Written by: Hannah Gibbons
	About the Author: Hannah Gibbons, an employee at Sow True Seed since 2020, has nearly a decade of experience in the agricultural industry. Their passion for environmental education and regenerative agriculture has been the cornerstone of their work, aimed at making gardening accessible to all.