Start a week before you go

Holiday watering starts long before you zip the suitcase. Most containers fail not because of one scorching afternoon but because the compost has been slowly drying out for days beforehand, so the week before you leave is the moment to build up some resilience.

Water deeply every morning rather than little and often. A thorough soak sends roots down into the cooler, damper layers of compost, while daily dribbles keep them near the surface where they bake. Stop feeding about a week before departure: soft, leafy growth fed on liquid tomato food wilts far faster than steady, slightly tougher growth.

Use the same week to deadhead and tidy. Spent flowers and seed heads are simply water going nowhere useful, and cutting them back reduces the leaf surface the plant has to keep supplied. Move pots into their holiday positions early too, so they have time to settle rather than sulking in shock.

Set up a wicking system for the thirsty ones

Wicking is the cheapest reliable trick in the book, and it works beautifully for tomatoes, courgettes, fuchsias and anything in a large pot. The principle is simple: a reservoir below or beside the container, and a fabric wick that draws moisture up into the compost by capillary action.

Here is a setup that takes ten minutes:

• Stand the pot in a deep tray or on a length of capillary matting, and keep the tray topped up with 2–3cm of water.
• For bigger pots, put a bucket or lidded container of water beside them, slightly higher than the pot.
• Cut a length of old cotton shoelace, thick string or a strip of capillary matting and bury one end 10cm deep in the compost, ideally near the centre.
• Drop the other end into the reservoir, weight it with a stone so it stays submerged, and mulch over the top of the pot to stop surface evaporation.
• Top up a plastic bottle, pierce two or three small holes near the base, and bury it neck-down in the compost as a slow-release reservoir for smaller pots.

Test the whole arrangement for at least two days before you go. If the compost is still damp 3cm below the surface after 48 hours, it will hold for a week. If it is dry, add a second wick or raise the reservoir.

Group pots and mulch the surface

Scattered pots each face the sun alone. Clustered together, they create their own humid microclimate, shade one another's compost and cut water loss dramatically — often by half or more. Push them into a tight block, with the tallest at the back and the thirstiest in the middle.

Then cover every exposed compost surface with 2–3cm of gravel, bark chippings, spent mushroom compost or even torn-up cardboard. Bare, damp compost in July sun is a wicking system running in reverse: it pulls water out and hands it to the air.

Move pots off hot paving, decking and concrete if you can — these radiate heat back all evening. Grass, gravel or bare soil is cooler, and a larger saucer under each pot gives you another shallow reservoir to fill. Double-potting, with a smaller pot tucked inside a larger one and damp newspaper packed between, also slows drying in exposed sites.

Shade is your cheapest ally

No gadget outperforms a bit of shade. Move containers to a north-facing wall, under a tree, or into the strip of shadow that runs along the side of a house or shed. A few feet can be the difference between damp compost and dust.

If you cannot move them, create shade. A length of shade netting, an old cotton sheet or a couple of bamboo canes with fleece draped over them will do for a week — just make sure air can still circulate underneath. Never wrap pots in plastic; you will cook them.

In a greenhouse or conservatory, damp down the floor with a bucket of water, open the vents wide, and stand pots on trays of wet gravel or capillary matting. If the forecast is for a proper heatwave, white shade paint on the glass is worth the job.

The night before, and the length of your trip

Water in the evening, when the compost is cool and there is a full night for it to soak in. Keep going until water runs freely from the drainage holes, then wait ten minutes and do it again — dry compost can be surprisingly stubborn about absorbing water the first time round. Fill every reservoir, tray and saucer, and check that wicks are still submerged.

For a long weekend — two or three nights — most established containers will simply come through on a good soak, some shade and a full saucer. Be less relaxed about a fortnight in August, especially for grow bags and small terracotta pots, which dry out fastest. Self-watering containers, a bath or deep tray lined with capillary matting and filled with 5cm of water, or a kind neighbour with a key will all see you through. On your return, water gradually rather than flooding bone-dry compost, and top up the mulch for the rest of the summer.