We can predict only that summer weather is unpredictable. There may be a heatwave, or we may have to stare out of the window at a month of torrential rain. Dealing with an excess or lack of water is one of summer's greatest challenges, and your garden will be easier to care for if you prepare for extremes.
Come extreme heat or wet, a garden created mostly from annuals will be worse off than one filled with perennial plants. Annuals are frost-sensitive and able to face the outdoors only from late spring, leaving them with still-developing root systems come summer. This is a tough way to face a drought or a flood. Perennials will spring from their sturdy root systems each year and prove far tougher customers.
Know what not to water
Assume most plants will be OK without your attentions, even in a drought. Perennials, trees, shrubs and lawns planted or sown more than six months ago will mostly be fine: if they aren't, it may be time to have a rethink. It's tempting to water your lawn in a prolonged drought, but don't. Come autumn, it will spring back like a soggy, green phoenix.
Hang on to as much rainwater as you can. Attach water butts to downpipes, sheds and greenhouses using a rain diverter kit. Even polytunnels can be used to collect water; tunnel gutters are tiny, flexible and adhesive, sticking to the plastic at a slight angle and trickling water into an open water butt.
Create a rain garden
Traditionally, water comes into gardens via mains taps and leaves via drains. Rain gardens keep rainwater longer. Make paving permeable, so water soaks through, and create green roofs that absorb storm water, then release it slowly. Scrap water features that run on mains water and install ones that make the most of the rain: think rainwater trickling down rain chains. All water is funnelled to a swale: a meandering semi-bog garden filled with plants that cope with wet or dry. Water drains slowly through the network of roots and soil. Hugo Bugg's waterscape garden at Chelsea was a masterclass in rain gardens.
Vegetable patches and areas of annual bedding do need watering in a drought, but check if they need it first. Plants in containers need watering throughout summer, often even in wet spells. A daily trickle of water encourages the formation of shallow roots across the surface of the soil, and these will suffer in drought. An occasional deep watering draws roots down. Cut the base from a plastic bottle and sink it neck first into the soil next to plants, then water directly into the bottle.
Pots and summer holidays
Group containers together so they create a humid microclimate and transpire less; if you can do this in a shady spot, all the better. I have several large black trays that I bought at garden centres on which I sit groups of pots. I fill the trays with water, which is slowly absorbed by the pots. If you are away for a longer spell, look into buying drip irrigation and a timer, or ask someone to water for you.