Fertilising is a different job from improving your soil, and it's worth keeping the two separate in your head. This site's soil type and composting articles cover structure, drainage and the organic matter that builds healthy soil over time. Fertiliser is more specific than that: it's about supplying the actual nutrients a plant draws on to grow, and the three that matter most are nitrogen, phosphorus and potassium, shown as three numbers on every fertiliser bag. Nitrogen drives leafy green growth, phosphorus supports root and flower development, and potassium underpins fruiting and overall plant health. A bed can have beautifully improved soil and still leave a heavy-feeding crop short of one of these three if nothing is actually feeding it.
A bed can have beautifully improved soil and still leave a heavy-feeding crop short of one of these three if nothing is actually feeding it.
Blood and bone is the most traditional choice for getting a new bed ready to plant. It's a slow-release organic fertiliser, heavy in nitrogen and phosphorus, and the standard way to use it is working it into the soil ahead of planting rather than sprinkling it around an already-growing crop. Because it releases gradually as soil organisms break it down, it needs time to start feeding a plant properly, so it suits preparing a bed one to two weeks before you plant into it far better than it suits trying to perk up something that's already struggling.
Sheep pellets are the mild, all-round option, and they're the most commonly used home garden fertiliser in New Zealand for good reason. They're gentle and slow-release, gentle enough that you can apply them more liberally than a synthetic fertiliser without the risk of burning roots that comes with overdoing something more concentrated. They're a sensible default for general feeding across a mixed vegetable bed when you don't want to think too hard about matching a specific product to a specific crop.
A general vegetable fertiliser blend is formulated to give a balanced spread of nitrogen, phosphorus and potassium across a bed growing several different crops at once, rather than being weighted toward one nutrient the way blood and bone is. It's a reasonable one-product answer for a typical home vegetable bed, though concentrations vary a lot between brands and between organic and synthetic formulations, so it's worth actually reading the application rate on the bag rather than guessing.
Liquid feeds, fish emulsion and seaweed-based liquid fertiliser being the two most common, work faster than anything granular because the nutrients are already dissolved and available to plant roots as soon as you water them in. That makes them the right tool for a quick top-up once a crop is actively growing or starting to fruit, rather than for the initial feed at planting time. The trade-off is that the effect doesn't last, so a liquid feed needs repeating every couple of weeks through a crop's most active growth to keep making a difference, unlike a granular feed that keeps releasing nutrients on its own for weeks after one application.
Different crops want different balances once they're actually growing. Leafy greens like lettuce and spinach are grown for leaf, so they respond well to feeding that leans nitrogen-forward. Fruiting crops shift partway through their season: a tomato plant benefits from that same nitrogen early on to bulk up its foliage, but once it starts flowering, comparatively more potassium serves it better, since too much nitrogen late in a tomato's season pushes leafy growth at the expense of the fruit you actually want. For a heavy feeder growing over a long season, tomatoes, sweetcorn and brassicas among them, one feed at planting time rarely carries a plant all the way through. Feeding again partway through the season, once the plant is established and putting real energy into growth or fruit, is standard practice rather than an optional extra.
It's worth remembering that over-fertilising is a genuine risk, not just a theoretical one. Too much fertiliser, especially a concentrated synthetic one applied heavily, can burn roots or push soft, sappy growth that pests find easier to target than a plant growing at a steady, well-fed pace. More is not automatically better once a plant's basic nutrient needs are being met, and a mild, slow-release feed applied at a sensible rate does more good over a season than an occasional heavy dose of something stronger.