Action plan: Nigel Colborn’s essential jobs for your garden this week
- Nigel Colborn says it’s safe to plant dahlias outside if mild weather continues
- He advises protecting young plants with horticultural fleece if temperature falls
- British gardening expert also offers a reader advice about their Oleander bush
PLANT OUT YOUNG DAHLIAS
Should the mild weather continue, it will soon be safe to plant dahlias outside. If you started your plants in a greenhouse, or potted up dry tubers earlier this year, they will have healthy shoots by now.
With care, turn your plants out of their pots. Try not to disturb the roots and if possible, keep the potting compost in place around them. Occasionally, loose tuber ‘fingers’ fall away from the plants. If that happens, don’t worry, the plants will still grow strongly.
I usually sprinkle a little bonemeal or slow-release fertiliser into the planting holes, before placing each dahlia plant. Make sure the tubers are set deeply enough, even if that means some of the shoots will be partially buried in the earth.
Nigel Colborn says it will soon be safe to plant dahlias (pictured) outside if the mild weather continues
After a few days to settle down, growth will resume. Medium and tall varieties will need support as soon as the stems begin to extend.
It is often easier to set up canes or metal supports while the plants are still short. I use interlinking metal stakes, but you can also support plants with bamboo or hazel canes and soft string.
Frost is still possible, even in late May. So if temperatures are forecast to fall below 2c, protect your young plants with horticultural fleece. It’s lightweight for young plants. Remove overnight protection every morning.
Bulbs of tulips that bloomed this spring can be re-used. If bulbs are left in the ground, they will come up again next spring. Tulip bulbs can also be lifted for re-planting next autumn. To do that, dig up your plants with the stems intact. Lay them on a tray and allow to dry. Later, remove the dead stems before storing the bulbs somewhere cool and dry.
If you potted up canna tubers this spring, it’s time to harden them off for life outdoors. The same applies to overwintered cannas, ginger lilies and other big sub-tropical plants. Cannas overwintered in greenhouses may need re-potting. With ginger lilies (Hedychium), plant the tubers with care in the ground or in large pots. Don’t plant too deeply but cover the rhizomes.
My four-year old Oleander bush has always come through winter unharmed. But this year most of the leaves went black. The stems are still green but so far, it shows no sign of recovery. What are its chances?
Nigel said columbines (pictured) enjoy well-drained but moist soil in sun or part shade
Mr B. Kennedy, via email.
It’s still too early to issue a death certificate. Oleanders are surprisingly tough and can take some frost. Your best bet is to remove all black leaves and prune away the dead stem tips.
Then, examine the plant. If parts of the stems are still green, recovery is likely. Leave the plant and wait for any new shoots.
As a precaution, this summer, select one or two new shoots in August. Root those in compost, in a windowsill pot and keep them frost-free all winter. Then, if needed, you’ll have replacement plants next May.
PLANT OF THE WEEK: AQUILEGIA CHRYSANTHA ‘YELLOW QUEEN’
Columbines have beautiful and fascinating flowers. Viewed in a group, they make a gently colourful show. But examine a single flower and you’ll be amazed at how intricate its design can be. Some American species have larger, more elegant flowers than our native columbines. One of the best, A. chrysantha, has big, yellow flowers with long, elegant spurs. Columbines enjoy well-drained but moist soil in sun or part shade. They look best when grown in loose groups.
Most are short-lived perennials, so allow the seed pods to ripen and self sow.
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