Alan Titchmarsh as identified a “magic” ingredient that helps plants grow “more rapidly than anything else” – and it's free.

As part of a series of tips on how to water your garden – and when not to water – Alan has said that rainwater has a “magic ingredient” that simply isn’t present in the water we get from the mains.

As a result, he says one of the most vital piece of equipment any gardener could buy is a water butt. On the Gardener’s World podcast, he explained: “The funny thing is, there’s something about rain.

“It’s got some sort of magic ingredient and plants always seem to grow more rapidly from rainwater, from water that comes out of the hosepipe.

“So make sure that there ware water butts on all your downpipes, so that you’re saving rainwater.” Alan adds that at his home, virtually every piece of guttering on his house feeds a water butt, rather than pouring its precious rainwater down the drain. He continued: “It gets used particularly for thing like rhododendrons, azaleas and camellias.”

Alan says that where he lives, the mains water comes from a hard-water area, with a good deal of calcium dissolved in it, so it’s not ideal for many flowers.

The BBC regular stressed that in many cases, gardeners tend to water their gardens too regularly. After a couple of weeks of fine weather, topsoil can start looking a little dry and dusty.

So Alan urges gardeners to do a quick check with a trowel. He suggests digging just an inch or so beneath the surface which will often show that, down where the plants’ roots are, the soil is still perfectly moist.

Alan went on to say that gardeners can often be tempted to give their lawns a good soaking if they start looking a little yellow, but that’s rarely necessary. “Do not water your lawn, let it go brown,” he added.

The expert explains that while the the surface of the grass may lose some of its colour after a spell of dry weather, “the resting buds” of the grass are waiting to recover as soon as the rain returns. And this being Britain, you will rarely have long to wait before it starts raining again.