I get some version of this question at almost every consult: "I want to amend my soil this year — what should I actually be adding?"
The honest answer is: it depends on what your soil is doing and what you're trying to grow. But there's a logical order to this, and once you understand it, the product labels at the garden centre stop being so overwhelming. I work with Hamilton gardeners on this constantly — here's how I walk through it.
Start with a quick diagnosis
Before you buy anything, spend five minutes with a shovel and a glass of water.
Dig down about 15–20 cm. Is the soil clumping in hard chunks, or does it break apart easily? Does water pool on top, or does it sink in? And do a quick home pH test:
- Soil + baking soda + water — if it fizzes, it's acidic
- Soil + water + vinegar — if that one fizzes, it's alkaline
This matters because pH controls whether nutrients in your soil are actually accessible to your plants. You can add all the amendments you want, but if the pH is off, your plants can't take them up. Diagnosis first, amendments second.
In Hamilton, most of us are sitting around 6.5 — slightly on the acidic side, thanks to our climate and bedrock. That's actually pretty workable for most gardens. The plants that struggle here without help are the acid-lovers: blueberries, azaleas, rhododendrons, and heathers, which want closer to 5.5. More on that in a minute.
A quick note on clay before you add anything
If you're dealing with heavy clay — which honestly describes most Hamilton gardens, especially in older neighbourhoods like Westdale, Kirkendall, and most of the lower city — there's one thing worth doing before amendments go in: give the soil somewhere to go.
Clay particles pack tightly together, which means anything you spread on top can sit there rather than working its way down to where the roots actually are. A fork changes that. Not a broadfork — I know those get recommended a lot, and they're a lovely tool if you have one, but they're an investment most home gardeners don't need to make. A standard garden fork does the job just fine.
Push it in, rock it gently back and forth, move along the bed. You're opening up channels without flipping the soil layers or disturbing the biology living in them — which is exactly the point. No-till doesn't mean no aeration. [this short video shows the technique I mean — worth a few minutes of your time]
Do this first, then topdress. The amendments have somewhere to travel, and your soil structure stays intact.
Step one: organic matter — always, and first
Before you reach for anything targeted, organic matter is the universal non-negotiable. It feeds the soil food web — the fungi, bacteria, and worms that make nutrients available to your plants — and it improves structure regardless of whether you're dealing with clay or something sandier.
Here's a quick breakdown of what's available and what each one brings:
Garden compost (homemade or bulk) — the all-rounder. Improves drainage in clay, water retention in sand, and feeds soil biology across the board. If you can only do one thing, do this. Topdress 3–5 cm in spring and let it work down — no tilling required.
Mushroom compost — the byproduct of mushroom growing. Contains nitrogen, potassium, and phosphorus, plus bonus calcium and magnesium. Slightly alkaline, so keep that in mind if you're already on the higher end of pH. Great as part of a mix.
Worm castings (vermicompost) — the premium option, and worth every penny for new beds or containers. Significantly richer in nitrogen, phosphorus, and potassium than standard topsoil, and it comes with a population of beneficial microbes. I use it sparingly and strategically rather than in bulk.
Composted manure (cow or poultry) — high in nitrogen, excellent for building volume in new beds. One firm note: use composted, not fresh, and skip horse manure entirely. There's a real risk of persistent herbicides from hay that don't break down through composting and can damage your garden for years.
Aged shredded leaves (leaf mold) — free, local, and underrated. Shred them with the mower in fall rather than bagging them. By spring they've broken down beautifully and add carbon and structure to whatever you're mixing them into.
For raised beds, you're aiming for a mix that's roughly half quality topsoil and the rest organic matter — not one type, but a few combined. For in-ground beds, an annual topdress of compost is usually enough to keep things moving in the right direction.
Step two: targeted amendments — match the amendment to the need
Once the organic base is sorted, you can layer in specific amendments based on what you're growing and what your soil is missing. Here's what I reach for and when:
Bone meal — phosphorus and calcium; slightly raises pH. Phosphorus supports root development, flowering, and fruiting, so this one earns its place when planting bulbs, perennials, or tomatoes. Mix a small handful into the planting hole rather than broadcasting broadly.
Blood meal — fast-release nitrogen; slightly lowers pH. Best for leafy, hungry crops: brassicas (cabbage, broccoli, kale), lettuce, and anything that's looking pale and stunted early in the season. Because it works quickly, go easy — a little at a time to avoid burning roots.
Greensand — slow-release potassium plus a range of micronutrients. Potassium builds drought tolerance and supports fruiting, so this one is particularly good for tomatoes, root vegetables, and anything that tends to wilt or produce poorly in dry stretches. It works slowly over a full season, so add it at planting time.
Gypsum — the underrated one for Hamilton gardens specifically. It helps loosen heavy clay by shifting the particle structure, and — importantly — it doesn't significantly change pH. If your soil is compacted and draining poorly, gypsum is a good first move before you work the fork through and start topdressing.
Dolomitic lime — raises pH and adds calcium and magnesium. The thing to reach for if your soil is too acidic for what you're growing. Brassicas love it. Also benefits lawns and tomatoes. Add it in fall if possible to give it time to work through the soil.
Elemental sulfur — lowers pH, slowly. The go-to for getting blueberries, azaleas, rhododendrons, and heathers to actually thrive in our climate rather than just survive. These plants genuinely need soil in the 5.0–5.5 range, and in Hamilton, that usually means actively managing pH year over year. Add it in small doses annually — results take one to two seasons, but they last.
A note on what not to reach for
Sand in clay soil — sounds logical, doesn't work. Unless you're adding it in enormous quantities, mixing sand into clay tends to make compaction worse, not better. Gypsum and compost are the right tools for clay.
Synthetic fertilizers as a first move — they feed the plant but not the soil. Think of it like coffee versus a real meal: you get a quick boost, but the underlying system doesn't improve. Organic amendments work more slowly but build something that lasts.
Random amendments without a plan — if your plants look off, don't just start adding things. Check pH, check moisture and drainage, check the roots before assuming it's a nutrient deficiency. A lot of "nutrient problems" are actually pH problems in disguise.
Where to find what you need in Hamilton
For bulk compost and topsoil, Millgrove Garden Supplies is my default recommendation — delivery available, good quality, and reasonable for volume work. For the more specific amendments — perlite, greensand, bone meal, blood meal, worm castings — Holland Park in Dundas has the best local selection I've come across.
If you're not sure where to start — or your garden has been underperforming and you can't figure out why — that's exactly what a consult is for. An hour together, a follow-up report you'll reference for years, and specific local shopping recommendations based on what your garden actually needs. Book a session here.