As the mercury rises, which plants should we be prioritising and are there some we shouldn't worry about watering?

As the heat of summer continues, many gardeners have become a slave to the watering can and hosepipe.

But will some plants take more drought than others? Will vegetables wither with little water, and what about our beloved borders and cherished containers?

RHS chief horticulturist Guy Barter offers some tips on how to prioritise your watering regime, especially if you are short on time...

1. Pots and hanging baskets

These should be your first priority, says Barter. And the smaller the pot, the more it's going to need watering, because less compost means less moisture is retained. "Pots naturally restrict the root volume, so need to be watered every day," he says. However, some plants will tolerate dry pots, including pelargoniums and lavender, so consider Mediterranean drought-lovers if you don't want to watering too often.

During really hot spells, you may also benefit from placing pots together in a shadier, sheltered spot out of the wind. The collection will create its own little micro-climate and there will be less evaporation, Barter notes.

"Place your pots into saucers to catch the overflow," he adds. "The pot will suck the water back up. It's also worth considering self-watering pots with a built-in reservoir of water, which can be very effective."

2. New plants

If you have new plants, which you have just planted out - whether seedlings, annuals, perennials, edibles, shrubs or trees - they will need watering while their roots develop.

"Newly planted things need watering every day to start with, and then every three days and five days when they gradually root out and start growing. This is for any plant you have planted since April, and don't forget things you planted last winter or the winter before," says Barter. "Trees and shrubs take a while to get going. After two years, they will probably be ok. With newly planted trees and shrubs, they will need a good soak every 10 days to wet the roots. After a couple of years, they can look after themselves."

Even drought-tolerant herbs such as sage, rosemary and thyme will still need watering for a few weeks if you plant them now, he says. But if you planted them a year ago in the ground, they shouldn't need watering, and their aromatic properties are enhanced by dry conditions.

3. Perennial borders

"The watering regime very much depends on what perennials you have in your border. Some are very drought-resistant, such as lupins, stachys and Phlomis russeliana (Turkish sage). Often, there's no need to water them at all," says Barter. "Other plants tend to come from prairie regions, like rudbeckias and echinaceas and phlox. These are regions that have summer rainfall, so they are not that tolerant of drought, particularly on sandy soils which don't hold a lot of water, and clay soils where the plants can't access water. Watering every 14 days may be enough, but it's got to be the right kind of watering.

"If you are planning a new border and want to make life easy for yourself, replace vulnerable plants in the autumn with more drought-resistant ones."

4. Vegetables

"I would water the area well before sowing seeds, letting it drain overnight. For transplants, I would water every couple of days until they get growing. When that happens you can water once a week. For crops - and you must remember that vegetables are mostly water so they do need watering - give them a really good soak every 10-14 days that completely wets the ground, and check with a trowel a couple of hours after watering, to make sure it's gone down where the roots are," Barter advises.

Freshly planted seedlings initially have to be watered every day, while transplanted veg will need watering every three to five days, he suggests. Once the crops are growing strongly and beginning to flower, that's the time to think about watering thoroughly every 10 days. "When lettuces form rosettes, water them then and that will get you 90% of the benefits of regular watering. Water beans when they come into flower."

Tomatoes will need watering regularly when they are in flower, otherwise they are prone to blossom end rot. Spasmodic watering can result in the skin of the fruit splitting.

5. Woodland plants

"Things like camellias and hydrangeas are intolerant of drought, so plant them in a bit of shade," says Barter.

How should you water?

"The worst thing you can do is little and often. You need to give mature perennials a thumping good soak, which would be two watering cans per square metre. Do that once every couple of weeks. If you water little and often, then much of the water will be wasted. It will evaporate and will never get to the roots."

Plants which won't need prioritising...

"Don't worry about established trees and shrubs including roses and fruit. In Britain, we don't have a dry climate, although we have dry spells. Established trees will go on happily in all but record-breaking droughts. They shed a few leaves at the back end of summer but they will recover in autumn, and the same goes for established shrubs," says Barter. "We never water our (mature) roses at RHS Garden Wisley - which is one of the driest gardens you can imagine. Give them a good mulch and feed them and they'll get all the moisture they need."

Grass also doesn't need prioritising, as long as you can tolerate a lawn which goes brown during summer. It will recover with the autumn rains. "Grass drinks up the most water. If you put a sprinkler on the lawn, vast quantities of water are lost. We advise against watering lawns," Barter notes.

And if all else fails...

"Plant drought-tolerant plants - anything with grey leaves, like Cistus 'Silver Pink', lamb's ear and lavenders and anything with waxy aromatic foliage, such as rosemary, sage, hyssop, thyme, plants with needle-like foliage such as santolina and many dwarf conifers, which are well adapted to resist moisture loss."