US Edition Dastardly duckweed
Mary Morley from Carmarthenshire and Jake from Walton-on-Thames are just two of several readers who want to control the tiny-leafed duckweed (Lemna minor) that invaded their ponds during the summer, and clearly missed my advice earlier in the year. This is a tough one.
Duckweed is often “donated” to ponds by visiting water birds, or attached unseen to pond plants, and can take hold without you noticing. In the worst cases a pond surface can become virtually covered in weed, causing serious stagnation problems. Duckweed growth slackens off considerably in winter, and this is a good time to scoop out as much as you can with a fine nylon net. Then, before any remaining scraps start to multiply in spring, use Duckweed Control from AquaHydrotech (ecopond.co.uk), which contains a natural bacterial culture that inhibits its future growth.
Nicky Saunders at Ecopond also recommends that both water mint and, in sufficient quantities, watercress (just chuck in bunches) also help to keep pond water clear, by feeding on the nutrients in the water that would otherwise support algae, duckweed and other undesirables.
White garden shrubs
I am trying to disguise or hide a new fence at the back of my garden in Surrey. It was planted by previous owners as a “white garden” and I am keen to stick to this colour scheme. I have bought some hellebores to plant in the area, which is lightly shaded for part of the day in summer by a neighbour’s birch, but would like ideas for some evergreen flowering shrubs that will grow to about 5ft in height.
Melody Cairns, via email
The shrub that immediately springs to mind if you want midsummer flowers is the white-flowered evergreen Escallonia iveyi, although with limited sun this might not flower as well as it should.
There are a couple of other bland, colour-free evergreens that do a good screening job and will cope with light shade. Elaeagnus ebbingei, which carries fairly insignificant white-ish flowers in very early autumn that smell heavenly (like lily-of-the-valley) has eye-catching silvery-bronze new summer leaves. Viburnum tinus might also be a good choice, flowering in spring and again in late summer if you are lucky. The variety 'French White’ has buds and flowers that are dead white instead of pinkish. These shrubs could be clothed, once established, with summer-flowering clematis such as white-flowered Clematis viticella 'Alba luxurians’ or C. 'Huldine’ if you gave them a bit of TLC to get them going.
But do you have to have flowers? There are other options: unless you dislike plants with variegated leaves (as so many gardeners do), you could go for either of the following that have evergreen-and-white leave: Pittosporum 'Silver Queen’, or Rhamnus alaterna 'Argenteomarginata’, Italian buckthorn.
They would both associate very well with your hellebores, I think, and could lighten the summer gloom at the back of your garden, too.
Maples for fall
Where can I buy a maple called, I think, 'Red Sunset’? I visited relatives in New England in the fall and I believe this is the name of one of the trees that particularly caught my eye. It was one among several with superb and long-lasting autumn colour.
Edgar Marshall, via email
This is indeed one of the best acers for autumn colour. Various tree specialists will be able to help you. I see that Barcham Trees (barcham.co.uk), for example, has this and several other varieties of Acer rubrum on their list.
And now for the slightly depressing bit. Autumns in North America are, I understand, both protracted and glorious not simply because of the species that grow there. Although, as with the ornamental Japanese maples we love to grow in our gardens, the big acers such as those that you saw turn a particularly good colour because the glucose trapped in their dying leaves happens to turn bright red.
The climate has a huge part to play as well, and consistently long, hot summers that give way suddenly to cold winters, as they do across the pond, we simply do not have. We do have many wonderful trees, including our native oaks of course, that colour up and give a spectacular show, but alas not brilliantly every year. And as I look out over my bedraggled garden, with the lawn awash with the huge saturated leaves of my tulip tree whose glorious colour came and went under pretty unrelentingly leaden skies this year, it strikes me that even with the right kind of leaves, we all too often have the wrong kind of autumn.
But don’t let me put you off. Go and find your 'Red Sunset’ and enjoy whatever it gives you as a reminder of your trip.
Finally, fungi…
A comforting word or two for P. Duffy, who says his (or indeed her) garden is “full of toadstools at the moment” (it probably isn’t by the time this appears; such is the nature of both the toadstools and this page). He/she asks if they will harm plants and what should be done about them. The vast majority of toadstools are harmless to plants, and are all part and parcel of the essential biology and general organic rot that goes on out there in the soil.
The toadstools that should ring alarm bells are those of honey fungus, which are not in evidence at this time of year, being generally thrown up in clusters from underground roots of their host plants in the summer. If rashes of autumn toadstools annoy, they can just be swept away with a broom.