Sowing and planting
Hardy annuals can be sown in pots or modules to provide colour in the garden. Annual grasses that can be fun to try too: Briza maxima, Lagurus ovatus and Hordeum jubatum are suitable examples. In mild areas with light soil, you can sow directly outside. Marking out irregularly shaped seedbeds and broadcasting ‘drifts’ of different seed gives a more natural look.
Modular trays are useful for sowing half-hardy summer bedding plants such as marigolds (Tagetes), Lobelia, and Petunia. Label each seed tray. You will need to plant them under cover, or in a heated propagator, at the appropriate temperature, only putting them outside when the weather is reliably warm day and night.
If you started sowing early, in March or even February, you may have modules of young hardy annuals now ready for planting out.
Sweet peas can be sown outside this month. Plant out autumn-sown sweet peas that have been raised in pots, and prepare your wigwam supports for them to climb, using a light twine to tie the plants in.
When space becomes available in the greenhouse, pot up cuttings of tender perennials taken last summer and at the beginning of this year. Bulk up plant numbers by taking more cuttings from the largest of the new plants.
Plant summer-flowering bulbs, if not done already. Prepare the soil first, to ensure that drainage is sufficient to prevent the bulbs rotting. Anemone coronaria tubers, for instance, need particularly well-drained soils.
You can still plant herbaceous perennials such as Geranium, Astrantia and Oriental poppies. Check that the plants you buy have strong, green shoots and plant them into well-prepared soil.
Plan a continuous crop of cut flowers for this summer. Perennials such as delphiniums and annuals can be grown to produce a useful and beautiful display.
Towards the end of the month, in mild areas, you may be able to plant up your hanging baskets for the summer.
Cutting back, pruning and dividing
Perennials that are showing new shoots from the crown can be propagated via basal stem cuttings. Shoots 8-10cm (3-4in) high are cut from the parent plant with a sharp knife. Sometimes a piece of root can be taken with the cutting (which speeds establishment), but stems can be cut without root, and then dipped in hormone rooting powder before striking into growing medium, as for softwood cuttings.
Divide clumps of herbaceous perennials that you want to propagate, those that have become too large for their allotted space, and those that are flowering poorly or have lost their shape. Bamboos and clumps of bulbs or rhizomes can be divided in the same way. Just make sure that the transplanted divisions have roots, shoots, and are given adequate water to settle into their new positions.
Prune penstemons and other slightly tender plants such as Teucrium and lavender. Make the cuts just above fresh, new shoots.
Some perennials benefit from having their flowering shoots thinned out. Although this results in fewer blooms, they are larger and of better quality. Delphiniums, lupins and phlox all benefit from this process.
General maintenance
Apply a general-purpose fertiliser to borders and beds. Take care not to damage emerging shoots, or to burn them with fertiliser.
Put supports in place for perennials before they get too large. Criss-crossing strings from hidden or decorative posts work well, allowing stems to grow up in the gaps between strings.
Remove faded daffodil and tulip flowers, nipping off the heads and seed pod at the same time.
Deadhead pansies, primulas and other spring bedding plants. Pansies will carry on into the spring and even to early summer, if attended to frequently.
Remove tired winter bedding and plants that did not survive the winter.
Check that self-seeded forget-me-not isn’t smothering other border plants. Pull out plants if necessary.
Hoe borders to prevent annual and perennial weeds from spreading and seeding themselves.
Herbaceous perennials infested with couch grass and other perennial weeds should be lifted so the roots of the weeds can be removed.
Bulbs coming up in the rock garden or in containers may benefit from overhead protection from the rain. A sheet of glass or Perspex placed on bricks will do the job.
Top dress spring-flowering alpines with grit or gravel to show off the plants and to help prevent stem rots. Any mulches may need replacing after weed removal.
You could plant up an alpine trough to display some of your alpine plants as many can look their best at this time of year.
Check whether containers need watering. Even at this time of year, they can dry out.
Pots and tubs benefit from topping up with fresh compost. Old compost can be removed and replaced with new to a depth of 5cm (2in) if there is not much room for topping up.
Pot on plants showing signs of being pot-bound. You can tip out the rootballs of unhappy looking containerised specimens, to see if they are indeed pot-bound or if they are suffering from some other problem.
Pest and disease watch
Continue to protect lilies, Delphinium, Hosta and other new shoots from slugs and snails.
Damage to plant roots by vine weevil larvae shows by the plants starting to wilt. On inspection the roots will have been badly eaten, and you may see larvae among them. Apply chemical or biological control if larvae are present, but young and containerised plants are unlikely to recover once badly damaged.
Aphids can multiply rapidly during mild spells. Remove early infestations by hand to prevent the problem getting out of hand. Protect sweet pea plants in particular, as they can get sweet pea viruses.
Watch out for downy mildew and black spot on winter pansies.
Remove dead leaves from around the basal rosettes of alpine plants to prevent rotting.
Top dress spring-flowering alpines with grit or gravel to show off the plants and help prevent rotting around the neck.