Action plan: Nigel Colborn’s essential jobs for your garden this week
- Nigel Colborn says mid-March is the perfect time to plant Gladiolus bulbs
- British gardening expert reveals they thrive best in free-draining soil with sun
- He also shares advice for a reader who wants to split polyanthus primulas
THE GLAD NEWS OF GLADIOLUS
Gladiolus, Britain’s most popular summer bulbs, are available now and selling fast.
Mid-March is the perfect time for planting them. They come in an amazing range of colours from purple through crimson or scarlet, toning down to yellow, cream or pure white.
Top-size corms will produce the largest flower spikes. But size isn’t everything.
Some of the smaller varieties make prettier garden plants and may blend more readily with your other border or patio plants. So have a good look through the catalogues, or at garden centre labels.
Nigel Colborn says mid-March is the perfect time to plant Gladiolus bulbs, revealing they thrive best in light
Gladioli are easy to grow. They do best in light, free-draining soils, in sunny positions.
When you receive the corms, plant them as soon as possible. Dig holes 10cm to 14cm deep and place the bulbs the right way up, before covering them. The upper side has a point or baby shoot at its centre. The bottom side usually has a discshaped root-plate at its centre.
If your soil is sticky or heavy, improve drainage by placing a double handful of grit or coarse sand in the bottom of the hole. Lay the corm on the grit before covering. The shoots will appear in a few weeks.
It’s important to remember that gladioli always face the sun. So if you can only view your plants from the north, they’ll probably face away from you.
DIVIDE AND PLANT PERENNIALS
If you grow hardy perennials, now is the time to lift, divide and replant. Almost all perennials benefit as, if left, they can lose vigour.
Select mature plants of nepetas, Michaelmas daisies, goldenrods and rudbeckias.
Using a large fork, dig up the entire plant. Save small, rooted sections from the edges of the clump. The sooner you replant the divisions, the quicker they will establish.
SWEET PEA SEASON
It’s time to sow sweet peas. The safest way is to plant your seeds into pots, filled with general purpose potting compost. Keep the pots in a cold frame or somewhere sheltered. Alternatively, sow the seeds directly into a prepared seed-bed.
The soil should be crumbly and friable. The seed will germinate readily. Sweet pea seedlings are vulnerable to pests so watch for slugs or snails and even fieldmice and voles.
Nigel chose erysimum ‘bowles’ mauve (pictured) as this week’s plant
PLANT OF THE WEEK: ERYSIMUM ‘BOWLES’ MAUVE
Unlike biennial bedding, this wallflower is perennial. It develops into a small shrub and mature plants grow up to a metre across and half as high. Healthy plants produce flushes of sideshoots, each ending in tight-packed flower buds. As days grow warmer, these bear rich mauve or purple fragrant flowers (above). The narrow leaves are a soft silver, maturing to glaucous grey. Though perennial, these plants grow leggy and untidy with age but are easy to propagate from soft cuttings. Take any time between now and September.
I set out a number of polyanthus primulas last year and had a grand show. This year they look great but have grown rather wide. Can I split them and, if so, when?
Phillip Blackwood, Hertfordshire.
You can. The best time is just after flowering; usually in May. But you can break the rules and split them earlier. If you do it when they are in flower, handle them carefully and water well after planting. If you dig them up after flowering, gently break the plants down. Then, with a sharp knife, cut away the oldest parts of the rhizomes the thick, knobbly horizontal parts of the root system. At the branched end of each rhizome you’ll find a rosette of leaves and a bud.
Remove the most healthy rosettes, making sure that each rhizome tip carries a few healthy roots. Plant them somewhere shady and keep them watered over summer. By autumn, you’ll have plump plants.