Here are your gardening jobs for the month – with added links if I have more information on the subject. They are all still relevant to do now if you’ve fallen behind or if the weather’s been bad.
Stop weeds before they start in earnest. Cover a weedy, empty patch of ground with black plastic, cardboard or carpet to stop unwanted plants growing until you have time to deal with them. On already cultivated ground, hoe weeds as they emerge and don’t let them seed. If you are blighted with perennial weeds such as bindweed and brambles, keep digging them out.
Russian comfrey plants – Bocking 14 – are a must to make your own plant food. The leaves can also be used as a compost activator, a mulch, or a liquid feed. Bocking 14 won’t take over your garden – but beware – the plant food it makes absolutely stinks!
Continue to prick out seedlings before they become straggly. Shade seedlings in the greenhouse on sunny days, as they can quickly wilt and die. Don’t water seedlings with cold water direct from the water-butt or hose pipe. Keep a couple of cans filled and inside the greenhouse so the water is at the ambient temperature.
Top-dress containers. Scrape the top 4cm/2ins of soil off, and replace with new compost. Finish with a layer of horticultural grit to retain moisture.
Make sure automatic vents in the greenhouse are working properly, and open the door on sunny days. Temperatures will soar inside a closed greenhouse. Avoid fungal diseases by watering from below to avoid wetting foliage. Don’t let plants stand in (still icy cold) water for longer than 10 minutes.
Feed hedges with a top-dressing of garden compost or well-rotted manure, or mulch with lawn mowings.
Plant evergreen hedges. Prepare the site well, adding a couple of handfuls of garden compost per plant. Water well over the next few months as the plants settle in.
There is still time to divide overgrown clumps of herbaceous perennials. Water well after transplanting, and keep moist in dry spells.
Slugs and snails will become very active. Most newly emerging shoots will be at risk. Act now and destroy their egg clusters, translucent milky spheres, usually laid in nooks and crannies in the soil, and down the sides of pots. Delphiniums and newly emerging hostas, in particular, are at risk. Once the soil has warmed up enough, apply the slug nematode. They will get rid of soil-dwelling slugs but not snails. Use all controls available. Don’t rely on just one method.
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.
The soil will be warming up at last, especially if you garden on clay. Delay seed sowing in open soil until you can see weeds growing strongly.
As weeds start to emerge and flourish, hoe regularly to stop them becoming a problem. Remember to check under cloches too. Get to know what vegetable seedlings look like, so you don’t hoe them off by mistake.
Dig in overwintered green manures three to four weeks before you want to use the ground. Using a sharp spade, turn the plants back into the soil, chopping them up as you go.
As climbing roses send out shoots, pull them down to the horizontal. This will encourage flowering shoots to emerge all along the stem.
Pot on dahlia and begonia tubers and pinch out tips of fuchsias and other half-hardy plants.
Sow perennials in modules or small pots. Prick out once leaves are large enough to handle. Plant out when well-established. Some perennials may flower this year, others will take longer.
Plant up hanging baskets. This gives them plenty of time to bulk up. If you use fuchsias, remember that they prefer shadier conditions, so sit them under the staging out of direct sunlight.
Pest populations usually start to increase dramatically now. Be vigilant and don’t allow infestations to build up. Use organic treatments, such as insecticidal soap, to control problems until the temperatures are warm enough for biological controls to be introduced.
Once it’s warm enough, introduce biological controls in the greenhouse. Use the predatory mite Phytoselius to control red spider mite, the tiny wasp Aphidius for aphids and the predatory mite Hypoaspis for control of sciarid fly.
Hard-prune shrubby herbs such as sage, cotton lavender (Santolina), bay and rue. This will encourage vigorous new growth and side-shoots. Trim old stems from marjoram and savory, if not already done. Prune lavender into shape, taking care not to cut into the old wood. Offcuts can be used as softwood cuttings. Old, woody plants are best removed.
Support peas sown last autumn or earlier this year, using twiggy sticks, or wide mesh netting. Prepare runner and climbing French bean supports if you want to save time later in the year.
Deadhead daffodils, but let the leaves die down naturally, to store food for next season’s display.
Tie in honeysuckle, clematis and other climbers as new growth starts to sprout.
On variegated plants, prune out shoots that have reverted to green. If left unchecked, they will eventually take over from the variegation.
Perennials should be staked early so they can be tied in unobtrusively before they start to flop. Use prunings from around the garden to make your own supports.
Feed the soil if your winter has been excessively wet. Use homemade garden compost, or well-rotted manure, around established plants, and in planting holes for new plants.
Tear off rose suckers. Cutting leaves a growth bud but tearing rips it off.
There are lots of annuals you can sow now including Californian poppy, Nigella and poached egg plants, which are good for pollinators.
To prevent algae build-up in your pond, add a small bale of barley straw, available from most garden centres, at £6-£7. As light levels and temperatures increase, this triggers algae growth in the pond, making the clear water go green. Have plenty of plants around the pond’s sides for moist shelter, essential if your pond is set in gravel.
Divide clumps of herbs that have become too large. Plants, such as bay, that are difficult to propagate otherwise, can be layered now. Refresh herbs growing in pots by scraping off the top 5cm/2” of compost, topping up with fresh and finishing off with a layer of horticultural grit to retain moisture.
Make sure annuals you buy at the garden centre/nursery are hardened off before you plant them out. Half-hardy annuals like Surfinia, petunias, French marigolds and Antirrhinum can’t go outside until your last frost date.
Wait until the soil is warm enough before planting potatoes – if grass and weeds are growing, it should be fine. If you got off to an early start last month with your spuds, then they may be ready for earthing up – covering the haulms with soil. Start this process as the shoots start to show, paying special attention if frosts are forecast. If frost is forecast, protect early, young potato shoots. They’ll need protection even in unheated greenhouses and tunnels, as well as outdoors. Earth them up or cover with newspaper, net curtain or horticultural fleece overnight.
Prune spring-flowering shrubs such as Forsythia, Ribes (flowering currant), Kerria japonica and winter jasmine. Next year’s flowers will be produced on stems growing over the coming months, so cut back hard now to get the shape you want for next spring. Wait until summer to prune magnolias such as M. stellata and M. x soulangeana.
Once the soil is warm and still moist, mulch well, to a depth of 6cm/3in. Use leaf mould or home-made compost if possible, to suppress weeds and help retain moisture levels right through the summer.
Plant out sweet peas and tie in if they are tall enough. Provide support with twigs or string or pea netting.
Hardy annual seeds can be sown directly into open ground, but wait until you can see weeds growing strongly before sowing.
Take cuttings from young shoots of shrubs. They should be putting on new growth now and will root easily.
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.
Divide clumps of herbaceous perennials that you want to propagate, those that have become too large for their allotted space. 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 Penstemon and other slightly tender plants such as Teucrium. Make the cuts just above fresh, new shoots.
Apply a general-purpose fertiliser to borders and beds. Take care not to damage emerging shoots, or to burn them with fertiliser.
Place card collars around the stems of brassicas to prevent an attack of cabbage root fly.
Sow pots of herbs such as parsley, coriander and basil.
Cover blossoming fruit trees with sheets of fleece on frosty nights to protect embryo fruit.
Sow seeds of the following veg if conditions are fine: beetroot, parsnips, turnips, onions, peas and mangetout, broad beans, lettuce and salad leaves, spinach, radish, rocket, mizuna, pak choi, cauliflower, cabbage and Brussels sprouts.