Why Even Moisture Matters More Than a Good Soaking

Tomatoes are fussy about rhythm. A plant that lurches from bone dry to sodden and back again will punish you, no matter how generous you are with the watering can. The two problems keen growers meet most often in a British dry spell both come down to inconsistency. Blossom end rot, that leathery black patch on the base of the fruit, is usually blamed on a lack of calcium in the soil, but in most gardens the calcium is there — it simply cannot travel to the fruit because the plant is not moving water steadily. Splitting is the other one: a dry fortnight followed by a thunderstorm, and every ripe tomato cracks along the shoulder.

The aim, then, is not to give your plants the most water. It is to give them roughly the same amount at roughly the same time, so growth never stalls and then surges.

Water Deeply at the Base, First Thing

Early morning is the best slot in the day. The soil is cool, evaporation is low, and any splash on the leaves has the whole day to dry off before evening, which reduces the risk of blight. Evening watering is a reasonable second choice, but wet foliage sitting overnight is asking for trouble.

Water the root zone, not the plant. Aim the spout at the base of the stem and let it soak in slowly rather than flooding the surface, which simply runs off. In open ground during hot weather, a good rule is around two to three litres per plant every two or three days — more if the soil is light and sandy, less on heavy clay that holds moisture well. It is far better to do this thoroughly twice a week than to sprinkle a little every day, because shallow watering encourages roots to stay near the surface where they bake.

• Water in two or three passes, letting the first soak away before adding more.
• Push a bottomless plastic bottle or small pot into the soil beside each plant and fill that, so water reaches down to the roots.
• Check the top 5cm of soil with your finger before watering again — if it is damp, wait.
• During a hosepipe ban, keep a water butt topped up and use grey water from the kitchen sparingly.

Mulch the Surface and Keep It Topped Up

A mulch is the single cheapest way to even out moisture in the soil. Spread 5–7cm of composted bark, straw, leafmould or dried grass clippings over the bed, leaving a small gap around each stem so it does not sit against the plant and cause rot. Always mulch onto already-damp soil; putting it on dry ground just traps the dryness underneath.

As well as slowing evaporation, a mulch keeps the soil temperature steadier and suppresses weeds that would otherwise compete for every drop. In a long dry spell it can easily halve how often you need to water. Top it up mid-season if it has settled to less than a couple of centimetres.

Containers and Growbags Need Daily Attention

Tomatoes in pots, growbags and hanging baskets dry out far faster than those in the ground, and the compost can go from damp to dust in a single hot afternoon. Check them before the heat of the day arrives — early morning, before you have your breakfast — rather than waiting until you notice drooping leaves at four o'clock.

• Stand pots in saucers or trays and fill them, letting the compost draw water up from below.
• Group containers together so they shade one another, and move them out of the fiercest midday sun if you can.
• Wrap or double-pot large containers to insulate the root ball, or slip a pot into a slightly larger one with damp newspaper between.
• Use capillary matting or a simple drip line on a timer if you are out at work all day.
• Feed with a high-potassium tomato feed once a week, applied to damp compost — never onto dry roots.

Learn to Read the Plants

Tomatoes tell you what they need if you look closely. Leaves that flag in the middle of a hot afternoon but perk up by evening are simply coping with heat; that is normal and no cause for panic. Leaves that are still limp first thing in the morning mean the roots are genuinely dry and you have left it too long.

Rolled, upward-curling leaves often signal heat stress or a sudden change in watering, while yellowing lower leaves can point to overwatering and soggy roots. If you know heavy rain is forecast, ease off for a day or two beforehand to reduce the chance of splitting. A cheap moisture meter, or simply the weight of a pot in your hand, is more reliable than guesswork.

A Simple Routine for a Dry Spell

In practice, consistency comes down to a short, repeatable routine. Walk the plot each morning with a watering can, check the soil at root level, and water deeply only where it is actually dry. Keep the mulch topped up, keep containers in saucers, feed once a week, and resist the urge to give a little extra "just in case" after a hot day.

If you are going away, sink a few plastic bottles filled with water, neck down, beside the plants so they seep slowly, or set a timer on a drip system. Do that, and your tomatoes will carry on swelling steadily through the driest fortnight that a British summer can throw at them — no blossom end rot, no cracked shoulders, and a crop that ripens evenly right through to the first frosts.