How do I keep the garden watered while I am on holiday?

Almost every guide to this starts with gadgets, which is the wrong end. The demand side is where the big wins are, because a plant in shade with fewer leaves and less fruit uses a fraction of the water of the same plant in full sun in flower. Reduce the demand first and the supply problem becomes much smaller and much cheaper to solve.

Step by step

1. Start a week early, not the night before.Anything you do to reduce demand — moving, cutting back, repotting a badly root-bound plant — is a check to the plant, and it needs a few days in its new position to settle before you leave. A pot moved into shade on the morning of departure has had no chance to adjust.
2. Move every container into shade.This is the single most effective free action. A pot in full sun can use several times the water of the same pot in light shade, because both evaporation from the compost surface and transpiration from the leaves fall sharply. Somewhere with morning sun and afternoon shade, or a north-facing wall, is ideal. Even the shady side of the house on a paved path will do.
3. Group the pots tightly together.Pots huddled in a block shade each other, raise the humidity between them and slow evaporation from the sides of every pot in the group. Put the smallest and most vulnerable in the middle where they are most sheltered, and the biggest and toughest around the outside.
4. Reduce the demand on each plant.Remove flowers, buds and developing fruit from anything ornamental, and pick every tomato and courgette that is close to ready. Flowering and fruiting are the most water-hungry things a plant does. On a leafy plant, taking off a third of the foliage is a legitimate trade if the alternative is losing it entirely.
5. Soak everything thoroughly the night before you go.Water until it runs freely from the base of every pot, wait twenty minutes, and do it again. One thorough soak that wets the whole rootball is worth several light waterings — a pot watered lightly is wet at the top and bone dry where the roots are.
6. Mulch every container and every vulnerable bed after watering.Mulch on top of wet compost holds the moisture in. Mulch on dry compost seals the dryness in and stops rain reaching it, which is why the order matters. Bark, compost, gravel or even a layer of newspaper under gravel all work on a pot.
7. Stand pots in trays or sink them into the ground.A saucer or a shallow tray of water under a pot buys a couple of days and is the cheapest supply-side measure there is. Do not do this to anything that resents wet feet — lavender, rosemary and most Mediterranean plants would rather be dry. Sinking a pot into a border or a spare patch of soil is better still, because the surrounding earth insulates the rootball and slows evaporation from the sides.
8. Set up an automatic system for anything beyond a week.A battery timer on an outside tap feeding a drip line or seep hose is inexpensive and reliable, and it is the only thing that genuinely works for two weeks or more. Set it up at least a week before you leave and watch it run so you find the leaks, the blocked emitters and the plant it does not reach while you are still there to fix them.
9. Prioritise honestly and say what you are giving up.Newly planted trees and shrubs, containers and anything cropping matter most. Established plants in the ground will look terrible and recover. Bedding and hanging baskets are the most likely losses and the least consequential. Decide in advance rather than trying to save everything.
10. Ask a person, and make it easy for them.A neighbour with a written list, the pots grouped in one place, the hose already connected and a note of what matters most is far more reliable than any gadget. Vague instructions produce vague watering. Leave a note that says which pots, how much, and how often.

Tips

• Greenhouse plants are the ones most likely to die while you are away, because a closed greenhouse in August cooks. Leave the vents and the door open, get shading on, and stand pots in trays of water — a greenhouse tomato in a growbag will not survive a fortnight otherwise.
• Hanging baskets are almost impossible to keep alive unattended. Take them down and stand them in a shaded tray on the ground; they will look untidy and they will live.
• A capillary mat on a tray, with one end in a reservoir, keeps seed trays and small pots going for well over a week and costs very little.
• Do not put pots in a paddling pool of water and leave them for two weeks. A day or two standing in water is a rescue; a fortnight is drowning, and the roots rot.
• Lawns need nothing. A brown lawn in August is dormant, not dead, and it will green up with rain. Spend nothing on it.

Common mistakes

• Leaving pots in full sun with a timer as insurance — It doubles or triples the water the system has to deliver and leaves no margin for a blocked emitter or a battery failure. Shade first, then irrigate what remains.
• Setting up the irrigation the night before leaving — Every automatic system has a fault on first run — a kinked line, an emitter that has popped off, a plant the spray misses. You need to be there for the first week to find it.
• Mulching dry compost — It locks the dryness in and sheds any rain that falls. Mulch always goes on after a thorough soak.
• Trying to keep everything alive — Spreading limited water and a neighbour's limited goodwill across the whole garden usually means the containers and new plantings that genuinely needed it get too little.

Checklist

• Containers moved to shade and grouped, a few days before leaving
• Flowers, buds and near-ripe fruit removed or picked
• Everything soaked thoroughly, twice, the evening before
• Mulch applied on top of wet compost, not dry
• Trays under anything that tolerates standing water
• Timer and drip line tested for a week beforehand
• Greenhouse shaded and vents left open
• Written instructions and a hose left ready for whoever is helping

Questions people ask