May 30, 2014 6:13 pm

Planting ideas for perfect window boxes, pots and containers

As ever, what looks most seductive now is most highly priced and usually least likely to last the course until late autumn
Bidens ferulifolia Golden Goddess©Fiona Lea/Gap Gardens

Bidens ferulifolia Golden Goddess

Plans for pots, patios and window boxes need to be finalised from today onwards. Late frosts have a way of teaching us a lesson every six years or so, but after the English Derby Day the odds on a ruinously cold night are much longer. What we choose now will condition the foreground of our summer, the flowery accompaniments to lunch outdoors, visitors’ arrivals and our first and last impressions as we go in and out of the garden between now and early November.

The stores and centres are full of possibilities, but those who are doing something last minute will usually have to pay for it. In London I have just been offered a single potted Cosmos daisy for £3.99 and a small pink-flowered oleander for £25. Individual potted petunias are priced at up to £2.99 each and geraniums come in at nearly £5 per plant. If you like scavenging, it is worth asking if your garden centre or local nursery has any “winter-flowering” pansies behind the scenes which it would like to sell off for a token £1. By now they will be looking straggly in a box, but if you split up their roots and cut back their stems to a few inches only, you can plant them round the edges of a pot in good loam compost. Keep them well watered and feed them fortnightly with liquid Phostrogen or Miracle-Gro. Most of them will send out masses of new shoots and soon flower all over again, providing an excellent foil for other summer plants that have been bought in at a price.

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Robin Lane Fox

As ever, what looks most seductive now is most highly priced and usually least likely to last the course until late autumn. For stamina, I recommend the lowly Bacopa plants which are usually offered when the flowers are still sparse and unobtrusive. The colours in the breeders’ varieties have continued to improve and the plants will make impressive carpets by late July. They will flower for weeks on end. The best white is Bacopa Snowflake, but I much like the pale pink Ring of Fire, which has a darker centre, and Lavender Blue, which is a soft colour too. Bacopas grow flat on the soil and are best planted near the edge of a pot and left to spill forwards over it. Cuttings will root with the greatest freedom and one way to economise is to buy two or three plants now and strip their stems at once for fresh cuttings, which are rootable in a pot of well-drained compost. The rooted cuttings can then be potted out in late June.

Bacopa Snowflake©Tim Gainey/Alamy

Bacopa Snowflake

As Bacopas show, breeders all over the world are as busy as ever, trying to produce bedding plants that have level, uniform top growth and a long season of flower in all weathers. The effects show on the season’s offering of petunias. I cannot see the point of the latest range of plants with small funnel-shaped flowers which have been called Littletunias by their humourless marketers. I want petunias with big open flowers like trombones. However, I can be tempted by clear scarlets and orange yellows in the related range sold as Million Bells. Correctly, they are Calibrachoas, not petunias, but be warned that their stems are fragile when first planted out. Twice, I have lost the best of mine to the antics of visitors’ dogs. If they survive, they will flower all summer, but they must not be swamped by neighbours in the same pot. The RHS Plant Finder lists only one supplier for each of the main varieties, but in fact they are all over the national garden centres this weekend. The Cabaret series includes a particularly deep violet-purple one, Purple Glow, which I recommend. Cabaret Apricot and Cabaret Bright Red are also good.

Verbenas have branched into new names, too. Again, the Plant Finder lists only one supplier of the new Verbena Lanai series, but I have found plants easily in London garden centres, usually labelled only “Lanai”. I have wondered how many forms to try, including one called Lanai Red which the Plant Finder does not yet catalogue. Verbenas are excellent value in pots and boxes, especially when deadheaded and cut back to half their stems’ length after the first flowering. They then regrow vigorously if fed on liquid fertiliser and will keep on going until the November frosts. The Lanai ones are said to be reliable, “uniform” and long-lasting. No doubt they are, but the Aztec series already is, and is even easier to find. I strongly recommend Verbena Aztec Silver Magic, a luminously pale lavender-white which trails widely and shows up superbly in mixed company. Bag it if you see it, even at £3.95 per plant. Cuttings will root quickly and flower in late summer. Alternatively, watch out for established favourites, such as the pale pink Verbena Silver Anne and the deep rich red Claret. Both of them survived the last winter and I am heavily into verbenas this year as a result. These potted, small perennial forms are far better than seed-raised “annual” ones, which are sold in strips of five or so.

Diascia Little Drifter©Penhow Nurseries

Diascia Little Drifter

At the Chelsea Flower Show, I had a tutorial on those other favourites, the much publicised Diascias. The expert exhibitors are Penhow Nurseries from Wales (penhownurseries.com) and in front of their big bowls of enviably flowery Nemesias and Diascias I learnt what most of us do wrong. We buy the bright coral pink, white or rose-coloured Diascias and enjoy a superb first flowering in June and July from these low-growing South African plants. We then cut them right back to ground level to encourage a second round but not much happens before autumn. We then try to split the plants up or at least to lift them and replant them in a frost-free place for next year. They then die.

Diascia management has to be more subtle. When we cut them back we should not cut them right down but we should leave about 3in of stem uncut, off which new shoots will then appear and flower all over again. In autumn the established plants hate being lifted. The best hybrids anyway refuse to be split up. The answer is to anticipate the frosts and simply take cuttings off the season’s best plants and then root them and winter them away from frost in a frame or cold house. The best nowadays, in Penhow’s opinion, are two hybrids which they stock and exhibit but which fewer garden centres offer, Diascia Little Drifter and Diascia Little Dazzler, a paler pink. I preferred the Drifter, but plants from Penhow will only be available now for booking and for delivery next April. Meanwhile, the most widely sold Diascias are forms which have had trouble from a deadly virus in the past 15 years. If yours have died off, you are not necessarily to blame.

Of course, bedders buy on impulse, which is half the fun of the whole extravagance. You will surely buy a few geraniums, some daisy-flowered Argyranthemums and flat, daisy-flowered Osteospermums, where the new dark purple-maroon Carita looks especially worth the price. Experiment freely, pack the plants in and tell yourself you saved on fuel all winter by not raising your own. What looks good now will not necessarily look the best in September. If in doubt, buy the unassuming, yellow-flowered Bidens, whose feathery growth will not seduce you yet. I say it most years, but for huge returns, value and long seasons, a Bidens trailing for several feet over the edge of a big pot or basket is still impossible to beat.

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