Soil Amendments and Fertilizers: A Guide to Building Better Garden Soil
Good garden soil starts with knowing what you have. There are three main soil types: clay, loam, and sand, and each benefits from compost, though the right amendment depends on which one you're working with.
How to Identify Your Soil Type
- Clay rolls into a tight ball and hardens into a lump.
- Loam crumbles easily in your hand, is dark in color, has no single dominant component, and isn't gritty.
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Sand crumbles with ease and won't retain water.
Best Soil Amendments for Clay, Sand, and Loam
All three soil types benefit from the addition of compost. We carry several bagged products to help build healthier soil when incorporated into your garden beds.
Leaf-Gro
Leaf compost that returns nutrition to the soil, helps sandy soils retain water, and allows clay soils to drain better. In loamy soil, it supports healthy root development by giving roots space for air and water to reach your plants.
Coast of Maine Compost Blend: Quoddy
Great for vegetable gardens, flower gardens, herbs, shrubs, and trees. Enriched with lobster and crab shell meal, manure, and aged bark, this product helps retain water in sandy soil or improve aeration in clay soil. It revitalizes soil and encourages root development. Spread 1 to 2 inches on the ground and till in. It's OMRI listed, so it's a fit if you're maintaining an organic garden.
Coast of Maine Penobscot Blend
A planting mix for trees, shrubs, and perennials. Well balanced, it contains manure, aged bark, mycorrhizae, and oyster shells, which provide calcium and support new root growth. Mix one-third Penobscot to two-thirds existing soil to encourage strong root development in new plantings.
Bagged Compost with Manure
A mixture of composted cow manure, mushroom compost, and sand with an NPK ratio of .5-.5-.5. Mix into raised beds, in-ground gardens, or around new trees, shrubs, and perennials at a rate of one-third compost to two-thirds soil. In garden beds, add 1.5 inches to the top of the soil and till into the top six inches.
Composted Black Kow
Dehydrated composted cow manure with an NPK ratio of .5-.5-.5, easy to work with. Mix with existing soil, using one-third Black Kow to two-thirds existing soil, for new trees, shrubs, and perennials. For poor ground, mix three bags into a four-by-six bed to a depth of three inches to improve the soil. This product also aerates wet soil and helps sandy soil retain water.
Mushroom Compost
A by-product of the mushroom growing industry. It may contain composted wood, straw, chicken manure, horse manure, gypsum, cocoa bean hulls, cottonseed hulls, and beneficial decomposing fungi. This product can carry higher salinity, so avoid using it around salt-sensitive plants.
All of these soil amendments help plant roots develop and spread, giving your plants a better chance of survival. We strongly recommend adding them at planting time. They also work well as a fall mulch, breaking down slowly into the soil over winter.
Browse our full soil and amendments selection to find the right product for your garden.
When to Fertilize After Planting
Once a new plant is in the ground, let it settle in for 2 to 4 weeks before fertilizing. Plants grown at nurseries are already treated in their growing mediums, so we recommend a half dose of fertilizer at first: you don't want to push the plant too hard early on.
If you're planting in fall, which is a great time to plant, skip fertilizing altogether. You never want to encourage new growth heading into winter.
When you do fertilize, use a well-balanced product with an NPK ratio that also includes micronutrients essential to plant health. Products with organically derived additives like kelp meal, fish emulsion, or worm castings are always a good addition.
Fertilizer Brands We Recommend
Organic Mechanics Fuhgeddaboudit!
A root zone fertilizer that comes premeasured. Just drop the pouch into the planting hole. It contains mycorrhizae, biochar, azomite, and oyster shell, all of which support root development.
Coast of Maine Stonington Blend
A great all-purpose fertilizer that promotes green leafy growth, budding, flowering, and fruiting. It can be used as a granular in garden beds, containers, or raised beds. It has a 5-2-4 ratio and contains lobster meal, kelp meal, and worm castings.
Espoma
Espoma products go beyond NPK with additional micronutrients for plant quality, including feather meal, crab meal, greensand, alfalfa meal, and bone meal. Each Espoma product is formulated for a specific plant group, so your plants get the nutrition they actually need.
Shop our full range of fertilizer and lime products, or stop by for garden supplies to help with application and soil prep.
Always read product labels and apply the recommended amount at the right time. These dosages are calculated to work as directed, and using too much can harm your plant.
FAQ: Soil Amendments and Fertilizers
How do I know what type of soil I have?
Clay rolls into a tight ball and hardens. Loam crumbles easily, is dark, and isn't gritty. Sand crumbles with ease and doesn't retain water.
When should I fertilize a newly planted tree or shrub?
Wait 2 to 4 weeks after planting, and use a half dose at first. Skip fertilizing entirely for fall plantings.
What's the best soil amendment for clay soil?
Compost blends like Coast of Maine Quoddy or Leaf-Gro help improve aeration and drainage in clay soil.
Can you over-fertilize a plant?
Yes. Always follow label directions. Applying more than recommended can harm the plant rather than help it.
