What to Add to Your Soil — and Why

A practical guide to organic amendments, rooted in 23 years of East Portland gardening.

In the winter of 2002–2003, I double-dug ten garden beds by hand in my front yard. I was young and energetic, and would dig for an hour every morning before heading to work. I joked that my garden was my "home gym." Nine beds were 4 by 25 feet, in neat rows separated by paths just wide enough for a wheelbarrow. The tenth ran perpendicular to the rows and was two feet wide and fifty feet long: the asparagus bed that is still producing today. As I dug each one, I amended the soil with a blend I had mixed myself: complete organic fertilizer, oyster shell, sand, and a little compost. I followed the recipe almost word-for-word from a book I had read cover to cover that fall.

The book was Growing Vegetables West of the Cascades by Steve Solomon.

The front yard food garden, April 2014

I grew up in Maryland, where my family kept a large vegetable garden and a hundred-foot greenhouse for starting plants. I knew how to garden. What I didn't know was how to garden here. The Pacific Northwest is not a forgiving place for gardeners trained in climates with real summers, predictable rainfall, and soils that aren't leached of nutrients by nine months of rain. Solomon gave me a new framework for when to plant, when to harvest, what the soil actually needed, and why. I’d been "soil curious," but this was my first serious introduction to soil science.

Twenty-three years later I'm still using what I learned from that book. I switched from mixing my own COF to buying a locally-made blend from Concentrates Inc., a Portland company since 1938 that Solomon himself mentioned in the book, which is how I found them. But the principles haven't changed.

This post is the practical companion to my post on Elaine Ingham's soil food web research. Ingham's work explains what's alive in your soil and why it matters. Solomon's work and this post answer the question that follows: So what do I actually add?

First, a Caution

Before getting into specific amendments, I want to echo something from the Ingham post: more is not better.

A 2020 OSU study of 27 Portland-area gardens found average organic matter at 13%, well above the recommended 3–5%. One garden hit 30%; the pepper plants died. Excess phosphorus from over-amended beds runs off into storm drains. Excess nitrogen leaches out before plants can use it. The goal is a functioning biological system, not a nutrient stockpile.

Amend to fix a deficit. Don't amend because amending feels productive.

If you're not sure where your beds stand, get a soil test. OSU Extension offers them at a reasonable cost, and their results include specific amendment recommendations for the Pacific Northwest. That test is worth more than any bag of fertilizer applied without knowing what your soil actually needs.

With that said, here's what I use, why, and for what crops.

Complete Organic Fertilizer (COF)

Steve Solomon developed his COF recipe specifically for Pacific Northwest soils, which are leached of nutrients by our wet winters in ways that soils in drier climates are not. The recipe calls for a blend of nitrogen, phosphorus, and potassium sources alongside calcium and trace minerals — a complete, balanced amendment that feeds soil biology and supplies the nutrients our specific conditions tend to deplete.

For years I mixed my own, using fish meal as my nitrogen source instead of seed meal. Solomon called fish meal the "rich man's" amendment, and he wasn't wrong about the cost, but it's faster acting in cold spring soils and I found it worth it for our climate. I eventually switched to buying Concentrates All-Purpose Fertilizer 5-5-3, which is based on the same principles and includes mycorrhizal fungi and trace minerals beyond what the base recipe provides. It is, as far as I can tell, as good or better than what I was mixing myself (considerably less work).

How to use it: 4–5 lbs per 100 square feet, worked into the top few inches of soil before planting. This is a general-purpose amendment for vegetable beds. Apply once at the start of the season and side-dress later if plants show signs of nitrogen deficiency.

For potatoes specifically: go light on nitrogen at planting. Too much early nitrogen pushes the plant toward foliage at the expense of tuber development. Use a reduced rate of COF and rely more on bone meal for phosphorus at planting time.

What it contains: fish bone meal, feather meal, flax seed meal, kelp meal, greensand, glacial rock dust, and sulfate of potash, plus trace minerals and mycorrhizal fungi. The kelp meal in the blend covers the micronutrient base that Solomon's original recipe addresses separately.

I carry Concentrates Complete Organics Fertilizer 5-5-3.

Bone Meal (3-15-0)

Bone meal is a high-phosphorus, low-nitrogen amendment, which makes it the right tool for situations where you want root development and tuber formation without pushing leafy growth.

For potatoes: phosphorus supports tuber development; excess nitrogen works against it. Work 2–3 tablespoons of bone meal into the soil below each seed potato at planting. A 1 lb bag covers roughly 5 lbs of seed potatoes.

For asparagus: phosphorus supports the deep root establishment that makes asparagus a 20-year investment rather than a two-year disappointment. Work 2–3 tablespoons per crown into the bottom of the planting trench.

For bulbs: the classic application. A tablespoon in the planting hole for tulips, daffodils, camas, and other bulbs supports root development through fall and winter.

For transplants generally: a small amount in the planting hole reduces transplant shock and supports establishment.

I carry Bone Meal 3-15-0, an organic powder from Pro-Pell-It.

Fish Bone Meal (4-17-0)

Fish bone meal has slightly higher phosphorus and nitrogen than standard bone meal, and breaks down a bit faster, which matters in cold spring soils where microbial activity is slow. It's also acceptable to many vegetarian and vegan gardeners who prefer to avoid mammal-derived inputs, which is worth knowing if that describes you or the people you're gardening with.

For tomatoes: phosphorus supports fruit development; the slightly higher nitrogen is welcome for a heavy-feeding crop. Work into the bed at planting alongside gypsum.

For general use: wherever you want a faster-acting phosphorus boost than standard bone meal provides.

I carry Concentrates Fish Bone Meal 4-17-0.

Gypsum (Calcium Sulfate)

Gypsum does two things that matter a lot in East Portland: it supplies calcium quickly, and it helps break up clay.

For clay soil: calcium ions from gypsum displace sodium and help clay particles aggregate: clumping together into the crumb structure that allows water, air, and roots to move through soil. If you've gardened in East Portland clay, you know exactly what compacted, poorly-draining soil feels like. Gypsum won't fix it overnight, but applied consistently it improves structure over time. It works in the same direction as the fungal networks Ingham describes, and the two approaches complement each other.

For tomatoes: calcium deficiency causes blossom end rot, that dark, sunken patch on the bottom of developing fruit that ruins a lot of Portland tomatoes. Gypsum is the right tool for in-season calcium supplementation because it works quickly and doesn't raise soil pH. Apply at planting and water-in well.

Important: consistent watering is as important as calcium supply for blossom end rot prevention. The plant can only move calcium to developing fruit when water uptake is steady. Uneven watering, dry spell followed by heavy irrigation, is the most common cause of blossom end rot even in calcium-adequate soil.

Gypsum does not raise soil pH. This makes it the right calcium source when your pH is already in range. If you need to raise pH as well, oyster shell or lime is the better tool.

I carry Microna Pro Gypsum (Organic/Granular).

Oyster Shell

Oyster shell is a long-term investment, not a quick fix. The coarse-ground oyster shell breaks down slowly over multiple seasons, gradually releasing calcium and gently raising soil pH. Don't apply it expecting to solve a calcium problem this year, it's building soil for next year and beyond.

For acid soils: Portland soils tend toward acidity due to our high rainfall leaching calcium and other base minerals. Oyster shell raises pH slowly and sustainably, which suits plants that prefer slightly alkaline conditions.

For asparagus: asparagus prefers a pH of 6.5–7.5. Work oyster shell into the bed at planting and reapply every few years. My asparagus bed has had oyster shell worked in since 2002.

For clay soil structure: calcium from oyster shell, like calcium from gypsum, supports the aggregation of clay particles over time. The difference is the timeline. Gypsum works within a season, oyster shell works over years.

For general soil building: a consistent, light annual application maintains calcium levels in soils that lose it to leaching over our wet winters.

A note on blossom end rot: coarse oyster shell will not prevent blossom end rot in the current season. Use gypsum for that. Apply oyster shell in fall or early spring for long-term soil building, with the expectation that it's working for your future garden, not this year's tomatoes.

I carry coarse ground oyster shell from Concentrates.

Putting It Together: Crop by Crop

Tomatoes: COF at planting + gypsum for in-season calcium + oyster shell worked in the previous fall for long-term pH and calcium. Consistent watering throughout the season.

Potatoes: light COF at planting + bone meal (3-15-0) below the seed potato + oyster shell for long-term calcium. Hold back on nitrogen early; side-dress with COF once plants are established if needed.

Asparagus: COF + fish bone meal + oyster shell worked into the planting trench. This is a 20-year bed — the investment at planting pays dividends for decades.

Bulbs: bone meal in the planting hole. That's usually enough.

General vegetable beds: COF at the start of the season, soil test to confirm you're not over-amending, and let the biology do the work.

Where I Get Everything

All of the amendments I carry come from Concentrates Inc. If you want to buy in larger quantities than I carry, they sell direct to the public.

Garden amendments are available here.

East Portland Plant Club carries vegetable seeds and starts selected for Pacific Northwest conditions, as well as PNW native plants and seeds. Our monthly pickups and seasonal sales are listed on the website and Facebook group.