April – a great time to plant summer flowering bulbs. Introduce some colour to your garden with alliums and agapanthus or lighten your garden with Lilium ‘Arena’.
You can still plant herbaceous perennials such as Geranium, Astrantia and Oriental poppies. Please remember that Anemone coronaria tubers need well-drained soils.
Propagate perennials that are showing new shoots from the crown with basal stem cuttings. Shoots 8-10 cm high is cut from the parent plant with a sharp knife. Divide clumps of herbaceous perennials if needed. Bamboo rhizomes and clumps of bulbs are divided in the same way. Make sure that transplanted divisions have roots, shoots and enough water to settle into positions.
Prune penstemons, Teucrium, lavender. Apply a general purpose fertiliser to borders and beds. Do not damage or burn emerging shoots. Put supports in place for perennials before they get too large. Deadhead pansies, primulas and other spring bedding plants. Hoe borders in order to prevent annual and perennial weeds from spreading. Top dress spring flowering alpines with grit or gravel to show off the plants. After weed removal replaces any mulches. Check whether containers need watering. Top up pots and tubs with fresh compost and remove old one.
Continue protecting lilies, delphiniums, hostas and other new shoots from slugs and snails. Apply biological control solutions if larvae are present. Aphids can multiply rapidly during mild spells. Early infestations can be removed by hand. Watch out for downy mildew and blackspot on winter pansies. Remove dead leaves from around the basal rosettes of alpine plants to prevent rotting.
Primarily, look round for BOX TREE MOTH, because they can completely defoliate box plants. It’s relatively NEW insect to Britain.
If the soil is not waterlogged you can still plant evergreen trees and shrubs, container-grown deciduous hedging plants and climbers, early in the month. Rabbit guards should be put in place while planting. Mulch rose and shrub beds with a 5- 7.5cm layer of organic matter. Mulch around rhododendrons, azaleas and camellias attentively adding ericaceous compost. Feed trees, shrubs and hedges with a balanced fertiliser sprinkling over root area before hoeing into the soil surface. Cut back Salix and Cornus at the beginning of the month. Prune back hard all the previous year’s growth to 1-2cm of the framework. Prune spring-flowering shrubs after flowering. Remove any frost damaged shoots from evergreens to prevent reversion taking over. Cut back lavenders lightly and treat Helichrysum similarly. Tie in and twin climbers such as honeysuckle and clematis around their supports. Tie in climbing and rambling roses horizontally to produce more flowers. Check if hardwood cuttings need planting out or potting on. Take cuttings of your favourite conifers. Propagate climbers and lax-stemmed shrubs by layering.
Phytophthora root rots can cause dieback on mature trees and shrubs. Check for damage or cankers on deciduous trees.
Avoid planting new roses in previous places to avoid replant disease. Inspect sick-looking box and holly trees for signs of blight. Once again look round for BOX TREE MOTH.
Mow lawns when necessary to maintain a constant height throughout the year. Add the clippings to the compost heap in thin layers. Use a half-moon edging iron or spade and create a 7.5cm gutter around the lawn edge to prevent grass creeping from the lawn into borders. At the beginning of the month apply a high nitrogen spring lawn fertiliser to encourage strong growth. Choose a combined fertiliser and moss killer if it’s a problem. Apply lawn weedkiller if needed but always follow instructions on the packaging very attentively. Remove old plant debris and rake lawns lightly. Repair bumps and hollows by peeling back the turf, removing or adding soil, and then replacing the turf.
Sow a wildflower meadow or plant wildflower plugs into existing swards. Help the lawn retain moisture by mulching. Mulch helps to keep it green rather than brown.
Feed large aquatic plants by inserting special aquatic slow-release fertiliser tablets around the bases. Feed any plants not being divided. Tidy up and mulch with composted bark plants in the bog garden. Divide or cut back marginal and bog garden plants if overcrowded. Divide and replant waterlilies if they show signs of growth.
Plant pond perennials in aquatic plant baskets and top with a layer of gravel. Small plants in baskets can be raised up on bricks.
Water can turn from clear to greenish because algae grow in the spring. Add more oxygenating plants to help clear the water.
Remove algae from paths with a pressure washer. Remove dirt and algae from walls, paving and patios. Check and repair pergolas, arbours and arches if needed. You can treat timber structures with wood preservative and stain in dry spells. Make sure you use appropriate products. Install decking or other seating areas for summer use.
Go through your shed and remove any old, out-of-date garden supplies.