Vegetables are hungry plants, and feeding them properly is the difference between a disappointing harvest and a generous one. But feeding is not one-size-fits-all: tomatoes, sweet corn and squash are heavy feeders that want regular food all season, while beans, peas and root vegetables want very little — and feeding them like tomatoes causes more harm than good. This guide covers vegetables fertilizing properly: which vegetables are heavy feeders, what NPK means in plain language, how compost fits in, when to side-dress, and the overfeeding mistakes to avoid. The timings and ratings below use published ranges for common vegetables, which vary by variety, climate and soil. As with everything in this guide, check your local extension service for advice suited to your area.
The first rule of fertilizing vegetables is to feed the soil first and the plant second. Compost dug into the bed before planting improves almost every soil, feeds soil life, and releases nutrients slowly all season. A bed with good compost needs far less fertiliser than a bed without it, and the vegetables taste better for it. Fertiliser is a supplement to good soil, not a substitute for it — a plant in poor, lifeless soil will not thrive no matter how much fertiliser you pour on it.
Heavy feeders, light feeders and nitrogen fixers
| Vegetable | Feeding group | Days to maturity | Feeding notes |
|---|---|---|---|
| Tomatoes | Heavy | 60–85 | Feed regularly once fruit sets; needs potassium for flavour |
| Sweet corn | Heavy | 60–90 | Hungry for nitrogen; side-dress when knee-high |
| Zucchini / squash | Heavy | 45–55 | Feed at planting and again when fruiting starts |
| Cucumbers | Heavy | 50–70 | Regular feeding; thirsty as well as hungry |
| Broccoli | Heavy | 60–85 | Feed at planting and when heads start to form |
| Cabbage | Heavy | 60–90 | Needs steady nitrogen for leaf growth |
| Cauliflower | Heavy | 55–80 | Hungry; sensitive to boron deficiency in poor soil |
| Lettuce | Moderate | 45–60 | Light feeding; too much nitrogen makes soft, sappy leaves |
| Onions | Moderate | 90–120 | Feed early; stop feeding as bulbs start to swell |
| Carrots | Light | 60–80 | Little feeding; fresh manure causes forking |
| Beets | Light | 50–70 | Little feeding; needs boron in poor soil |
| Radishes | Light | 25–40 | Almost no feeding; too fast to need it |
| Green beans | Nitrogen fixer | 50–65 | Needs almost no nitrogen; feeds itself |
| Peas | Nitrogen fixer | 60–70 | Needs almost no nitrogen; feeds the next crop too |
Tomatoes are the classic heavy feeder: they need feeding from the time the first fruit sets until the end of the season, and they need potassium in particular for flavour and disease resistance. Sweet corn is the hungriest of all — it wants nitrogen at planting and again when it is knee-high, and pale, stunted corn is almost always hungry corn. Brassicas — broccoli, cabbage, cauliflower, kale — are heavy feeders too, because they grow a lot of leaf in a short time. At the other end, carrots and radishes need almost no feeding at all: they grow fast, and too much nitrogen produces leafy tops and small, forked roots. Beans and peas are in a group of their own: they fix nitrogen from the air through bacteria on their roots, so they need little or no nitrogen fertiliser, and they leave nitrogen behind for whatever you plant next. The growing guide for tomatoes and the growing guide for broccoli cover the two most demanding vegetables in detail, and the fertiliser calculator works out rates for your beds.
NPK in plain language
Fertiliser labels show three numbers — NPK — which stand for nitrogen (N), phosphorus (P) and potassium (K). Nitrogen grows leaves: it is what leafy vegetables such as lettuce, kale and cabbage need most, and what makes lawns green. Phosphorus grows roots and flowers: it matters most at planting time and for root vegetables such as carrots and beets. Potassium grows fruit and builds disease resistance: it is what tomatoes, peppers, cucumbers and squash need most once they start fruiting. A balanced fertiliser, with roughly equal numbers, is a safe general choice for most vegetables. A high-nitrogen fertiliser is useful for leafy vegetables early in the season but harmful for fruiting vegetables later on — it produces lush leaves and few fruit. A high-potassium fertiliser, often sold as tomato feed, is the right choice once tomatoes, peppers and cucumbers start to fruit.
The numbers on the packet are percentages by weight, so a 10-10-10 fertiliser contains 10 percent of each nutrient. Always follow the packet rate: more is not better, and overfeeding can scorch roots, pollute waterways, and produce soft, disease-prone growth. If you are unsure, use half the recommended rate and see how the plants respond. The fertilising vegetables guide covers the general principles, and the fish emulsion fertiliser guide covers one of the most popular liquid feeds for vegetables.
Compost: the foundation of feeding
Compost is the best fertiliser for most vegetables, because it does more than feed: it improves soil structure, holds moisture, feeds soil life, and releases nutrients slowly over months. Dig 2–3 inches of well-rotted compost into the bed before planting, and top-dress with another inch during the season for heavy feeders. Well-rotted means dark, crumbly and sweet-smelling — fresh manure and unfinished compost can burn roots and carry weed seeds, and fresh manure on carrots causes them to fork. The composting basics guide and the compost ratio guide explain how to make good compost, and the compost tea guide covers liquid compost feed.
Manure is compost's stronger cousin: well-rotted farmyard manure is excellent for heavy feeders such as tomatoes, squash and brassicas, but it must be well rotted — at least six months old — before use. Fresh manure burns roots, carries weed seeds, and can contaminate leafy vegetables. Never use fresh manure on carrots, parsnips or beets: it makes the roots fork and grow hairy. Blood meal is a fast nitrogen boost for leafy vegetables, bone meal supplies phosphorus for root growth, and wood ash supplies potassium — but use ash sparingly, since it raises soil pH. The blood meal fertiliser guide and the bone meal fertiliser guide cover both in detail.
Side-dressing and liquid feeding
Side-dressing means feeding plants during the growing season, by scattering fertiliser or compost in a band alongside the row and watering it in. It is how you keep heavy feeders going after the compost dug in at planting runs out. Side-dress tomatoes when the first fruit sets, and again a month later. Side-dress sweet corn when it is knee-high, and again when tassels appear. Side-dress brassicas when heads start to form. Keep fertiliser a few inches away from stems, water it in well, and never side-dress dry soil — water first, feed second, water again.
Liquid feeding is faster: a liquid fertiliser or compost tea, applied every one to two weeks, reaches the roots within days. It is ideal for container vegetables, which run out of food fast, and for giving a struggling plant a quick boost. Feed after watering, not onto dry soil, and feed in the morning or evening rather than in the heat of the day. Stop feeding lettuce and leafy vegetables a week or two before harvest, so the leaves are not soft and sappy. The fertiliser calculator helps with rates, and the vegetables watering guide covers the watering that makes feeding work.
Signs of hunger and signs of overfeeding
A hungry vegetable tells you clearly. Pale, yellowish leaves — especially older leaves turning yellow first — usually mean nitrogen shortage. Purple-tinged leaves and slow growth can mean phosphorus shortage. Poor fruit set, small fruit and weak stems can mean potassium shortage. But yellowing leaves can also mean overwatering, cold soil or disease, so check the basics first: is the soil moist but not waterlogged, is the weather warm enough, and are the roots healthy? Feed only if the plant is otherwise well cared for and still looks hungry.
Overfeeding is just as visible: lush, dark green leaves with few or no flowers or fruit; soft, sappy growth that attracts aphids and flops over; scorched leaf edges from fertiliser burn; and, in the worst cases, dead roots. Overfed tomatoes produce leaves instead of fruit, overfed lettuce produces soft leaves that rot quickly, and overfed carrots produce forked roots. If you suspect overfeeding, stop feeding, water deeply to flush excess salts from the soil, and let the plant recover before feeding again — at half the rate.
Common fertilizing mistakes
- Feeding all vegetables the same, so carrots get tomato feed and beans get nitrogen they do not need.
- Using fresh manure on root vegetables, so carrots fork.
- Feeding tomatoes with high-nitrogen fertiliser after fruit sets, so they produce leaves instead of fruit.
- Overfeeding, so plants grow soft, sappy and disease-prone.
- Never feeding heavy feeders, so tomatoes and corn run out of food halfway through the season.
- Scattering fertiliser onto dry soil and not watering it in, so it scorches roots.
- Feeding lettuce right up to harvest, so the leaves are soft and spoil quickly.
- Forgetting compost — the foundation that makes fertiliser work properly.
Most fertilizing mistakes come from treating fertiliser as a cure-all. Feed the soil with compost first, match the feed to the vegetable, follow the packet rate, and watch the plants. They will tell you what they need.
Frequently asked questions
How often should I fertilize vegetables?
Heavy feeders such as tomatoes, corn and squash benefit from feeding every two to four weeks once they start fruiting. Light feeders such as carrots and radishes need little or no feeding beyond compost dug in at planting.
What is the best fertilizer for tomatoes?
A balanced fertiliser at planting, then a high-potassium feed — tomato feed — once the first fruit sets. Tomatoes need potassium for flavour and disease resistance.
Can I use fresh manure on vegetables?
No — use only well-rotted manure, at least six months old. Fresh manure burns roots and causes carrots to fork. Check your local extension service for guidance on safe manure use in your area.
Do beans and peas need fertilizer?
Very little nitrogen — they fix their own from the air. A little compost at planting is enough, and they leave nitrogen behind for the next crop.
Why are my tomato plants all leaves and no fruit?
Usually too much nitrogen, especially if you fed them with a high-nitrogen fertiliser after fruit set. Switch to a high-potassium feed, and stop feeding so heavily.
Related guides
For more vegetable help, browse the guides hub and the growing guides hub, and try the fertiliser calculator. Good next reads are the vegetables watering guide, the vegetables soil preparation guide, and the fertilising vegetables guide. And as always, check your local extension service — local advice beats any general guide for your soil, your weather and your varieties.