How to Water and Feed Tomatoes for a Heavy Crop

Getting a heavy crop of tomatoes comes down to two unglamorous habits: watering steadily and feeding at the right moment. Plants that are looked after this way set more fruit, ripen it more evenly, and shrug off the problems that ruin a season. None of it is difficult — it just needs to be regular.

This guide covers how often and how much to water, when to switch from general growth to a high-potash feed, and the small tricks that hold moisture so the fruit doesn't split. It builds on the main tomato guide, so if you're starting from scratch read that first, then come back here for the watering and feeding detail.

Why consistency is everything

If there's one thing that separates a good tomato crop from a frustrating one, it's even watering. Tomatoes are not fussy about how much water they get in absolute terms, but they hate sudden change — and almost every common fruit problem traces back to it.

When a plant is allowed to dry out and is then flooded, the fruit takes up water faster than the skin can stretch, and it splits. You'll see rings of cracks around the top or long splits down the side. The fruit is still edible if you catch it quickly, but it spoils fast and lets in mould.

The same erratic watering causes blossom end rot, the sunken brown-black patch on the base of the fruit. It looks like a disease but it isn't — it's the plant failing to move enough calcium into the fruit, and dry-then-wet soil is the usual reason. The calcium is almost always there in the compost; the plant just can't take it up steadily when the moisture keeps swinging.

So the goal is boring, in the best way: keep the soil evenly moist, all the time, from the first flowers to the last harvest. Get that right and you've prevented two of the three things most likely to spoil your fruit.

How often and how much to water

How much you water depends on where the plant is growing, the weather, and the size of the plant. A young tomato in May needs a fraction of what a fully grown, fruiting plant needs in a July heatwave. Use these as starting points and adjust to what you see.

Plants in the ground have the easiest life. Their roots can reach down for moisture, so they need watering less often — every two to three days in warm weather, more in a long dry spell. Give each plant a good soaking (a full watering can or so) rather than a daily splash, which only wets the surface and encourages shallow roots.

Plants in pots dry out far faster because there's a limited reservoir of compost. In summer they usually need watering once a day, and in real heat twice a day. A 30cm pot or larger holds moisture much better than a small one, which is why a generous container is worth it. There's more on this in the guide to growing tomatoes in pots.

Growbags are the trickiest of all. They hold very little compost for the number of plants packed in, so they dry out quickly and unevenly. Water little and often, and consider standing the bag in a tray or cutting the base to sit it on soil so the roots can wander out.

A few rules that apply everywhere:

• Water at the base, not over the leaves. Wet foliage in the evening invites blight and mould. Aim the can at the compost around the stem.
• Water in the morning where you can. The plant has the whole day to use it, and the surface dries before nightfall. Evening is the next best option in hot weather.
• Soak, then leave. A deep drink every day or two beats a daily dribble. You want the water to reach the deeper roots.

Signs you're getting it wrong: wilting in the heat of the day that recovers by evening is normal and not a worry. Persistent wilting, lower leaves yellowing, and dry, dusty compost mean it's too dry. Conversely, yellowing leaves combined with soggy compost, or a sour smell, point to overwatering and waterlogged roots. If the leaves are yellowing and you're not sure which way it's gone, the guide to yellowing tomato leaves walks through the causes.

Mulching to hold moisture

The single easiest way to keep moisture even — and to cut how often you water — is to spread a mulch over the soil around the base of each plant. A mulch is simply a layer of material laid on the surface; it slows evaporation, smooths out the wet-dry swings, and keeps weeds down at the same time.

For tomatoes in the ground, a 3–5cm layer of garden compost, well-rotted manure or grass clippings works well. For pots, a thinner layer of compost or even a few flat stones over the surface makes a noticeable difference on hot days. Leave a small gap around the stem itself so it doesn't sit damp.

The effect is real: a mulched plant can often go a full day longer between waterings than a bare one, and the steadier moisture is exactly what prevents splitting and blossom end rot. If you're improving your beds anyway, the guide to improving your soil covers building the kind of moisture-holding soil that makes all of this easier.

When and what to feed

Feeding is about timing as much as product. Tomatoes need different things at different stages, and the most common mistake is feeding the wrong thing too early.

Early on, the plant is building leaves and stems, and for that it wants nitrogen. If you potted into fresh, good-quality compost, there's already enough nitrogen in there for the first few weeks — you don't need to add anything. A plant pushed with extra nitrogen at this stage just grows lush, leafy and reluctant to flower, which is the opposite of what you want.

Once the first flower truss has set — meaning you can see tiny fruit forming behind the flowers — switch to a weekly high-potash tomato feed. Potash (potassium) is what drives flowering, fruit set and ripening, and the bottled "tomato feeds" you'll find at any garden centre are formulated for exactly this. Follow the dilution on the bottle and apply once a week with your normal watering.

Container plants need more feeding than plants in the ground, simply because there's less compost holding nutrients and you're flushing it through with frequent watering. By high summer a vigorous tomato in a pot may appreciate feeding twice a week at half strength rather than once at full strength — little and often suits them.

A note on overdoing it: more feed does not mean more tomatoes. Stick to the recommended rate. Overfeeding can scorch roots and actually worsen problems like blossom end rot by upsetting how the plant takes up calcium.

A simple weekly routine through the season

Pulled together, here's what a season looks like once the plants are outside and growing:

• May to mid-June (young plants): Water to keep the compost evenly moist, every day or two depending on the weather. No feed yet — the compost is doing the work. Mulch once the soil warms up.
• From first fruit set (usually mid-June onwards): Start a weekly high-potash tomato feed. Keep watering consistently — daily for pots and growbags in warm weather, every couple of days in the ground.
• High summer (July–August, full crop): This is peak demand. Pots may need watering once or twice a day; ground plants every two to three days. Feed weekly, or twice weekly at half strength for containers. Pinch out side shoots on cordon types so energy goes into fruit.
• Late summer into September: As light fades and growth slows, ease off slightly on water and feed. Remove the lower leaves to let air and light onto the ripening fruit.

Keep it simple: water in the morning, feed on the same day each week so you don't forget, and check pots daily in hot spells. If you want to line this up against UK sowing and planting dates, the planting calendar shows the timings for your area.

Watering while you're away

A week away in July is when tomatoes most often come to grief, because pots can't go more than a day or two without water in summer. A bit of planning saves the crop.

The easiest fix is to move pots into light shade and group them together, then stand each one in a deep tray of water so the compost wicks it up from below. Mulch helps here too. For a longer trip, a simple drip system on a timer, or self-watering containers with a built-in reservoir, takes the worry out of it entirely — both are widely available and inexpensive. The guide to growing tomatoes in pots goes further into container setups that cope better with a few days' neglect.

A friendly neighbour with clear instructions ("a full can per pot, every morning, at the base") is still the most reliable option of all.

Get the watering steady and the feeding timed, and the rest of tomato growing largely looks after itself. For everything from choosing varieties to dealing with problems, head back to the main tomato guide.