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One of the star performers of the last month at Gravetye has been magenta-flowered Geranium psilostemon. We’ve dotted it through the flower garden, where it combines well with Nepeta Six Hill Giant, foxgloves and lupins, but it’s most effective seen en masse in one of our borders, with Ammi majus reaching through its thick mounds. They’ve been in full flower since the start of June, but that particular display will soon be coming to an end when we cut the geraniums back to the ground. This is to prevent what was a beautiful sight turning in to a tired old mess.

It’s amazing how quickly new leaves appear, and their fresh green colour is a welcome sight in high summer. But before they emerge, it’s worth inter-planting, to take the flowering display deep in to autumn; for this, cosmos are perfect.

We sowed our cosmos back in May and are using a variety called Psyche White. It reaches about 4ft tall, with pure-white, semi-double, ruffled flowers that are just that little bit more interesting than the better-known, single-flowered Purity. They’re now looking handsome, having been grown on in three-litre pots, and are strong enough to push up through the geranium leaves.

A shorter alternative is Sonata White, which only reaches 2ft tall and is very effective at the front of the border. The Sonata series also comes in pink and, my favourite, carmine, its crimson flowers complimenting the dark-purple foliage of some of the dahlias.

If you haven’t had the chance to grow some cosmos of your own, the garden centres are full of them at this time of year and I always think it is well worth the investment to add some extra fun to the garden through the late summer.

We’re planting a lot of dahlias at the moment, in blocks and drifts, to replace the foxgloves. We store our dahlias through the winter in crates of compost in a cool cellar and wait until May to take the tubers out in to the sunshine. Then, we divide the clumps to increase our stock, and pot them up to grow on in a deep cold frame.

We began planting them out in early June this year, but continued potting on the leftovers; those are big plants now, which we’ll slot in to any gaps-this technique gives the border an immediate lift. As we grow so many dahlias, any that don’t make it to the borders are planted out in the kitchen garden to be used as cut flowers; we find we can never have too many of them!

There are so many different kinds of dahlia that one can be found for almost any occasion and it’s always fun to try out new ones. Magenta Star is one of my current favorites, with flowers, as the name suggests, contrasting with strong dark-bronze foliage. Dove grove is also a good one, with dark-red single flowers and purplish-green foliage.

David Howard is even better: its smoky dark foliage and rich orange flowers should be interesting where we’ve planted it this year, against the straw-coloured oats Stipa gigantea and the crimson-purple flowers of Cirsium rivulare.

These are all reliable dahlias, but a new one to me is a wild collected species, Dahlia australis, with simple lilac flowers. It’s available from Crûg Farm Nursery in North Wales (www.crug-farm.co.uk), although mine was a gift from a friend who managed to get it into flower last year on 6ft stems.

The sheer variety of dahlias available means that their differing forms can evoke either joy or revulsion, so if you want to refine your personal tastes, take a trip to Wisley garden later in the summer. It has all of the tried-and-tested old favourites in the borders, with big plastic labels for reference, and, on the trials field, there are 86 new varieties growing side by side for comparison. Take a notebook, so that any you like can be ordered for next year.

A useful service is the National Dahlia Collection in Cornwall (www.national-dahlia-collection.
co.uk), which takes online orders for cuttings to be despatched next spring.

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