Caring for perennials

Delphiniums, asters or coneflowers bring colour to the border, while ferns, barrenwort and hostas charm in the shade. Perennial borders are far less work than the common prejudice suggests – combining perennials according to their vigour and site requirements saves a lot of unnecessary gardening. But you can't manage entirely without secateurs, spade and fertiliser.

Establishment phase: watering correctly

Newly planted perennials don't yet have enough roots to draw water from deeper soil layers. Until they have rooted, the rule is: one thorough watering is better than several small ones. Water with a sprinkler or a fine watering rose – like gentle steady rain – and in hot weather always early in the morning or late in the afternoon, otherwise more water evaporates than the plants can absorb.

As a guideline, perennial beds need about 5–10 litres per square metre per watering. The soil in the root zone should be sufficiently moist to a depth of about 20 cm; sandy soils – such as on the Munich gravel plain – need more water than loamy or clay soils. Curled, limp leaves or premature leaf drop are warning signs.

Weeds and mulch

Keep planted areas free of weeds, as they compete with the young perennials for water, light and nutrients. Loosen the soil regularly and hoe shallowly to avoid damaging the roots. A mulch layer of 3–5 cm (compost, bark mulch, wood chippings or mineral mulch such as lava or grit) suppresses weeds and reduces drying out – but it absorbs some of the water and fertiliser, which then needs to be topped up.

Feeding

The type and frequency of fertiliser depend on the site and the plant's needs: border perennials need more nutrients than rock garden plants. A spring feed with organic fertiliser works well, as it lasts longer than mineral fertiliser. In general, organic-mineral slow-release fertilisers are applied from roughly early April to the end of July – not after that, so the plants can harden off. Do not use fast-acting fertilisers, and follow the product instructions strictly.

Pruning

Most perennials are cut back close to the ground at the end of the growing season in late autumn. For frost-sensitive varieties, the old shoots stay in place until spring as natural winter protection. Cutting off spent flowers encourages bud formation: cut delphiniums, catmint and sage back to 10 cm after flowering and they will produce a second flush; taller perennials only to 15–20 cm. Support and tie in tall perennials in good time.

Dividing and winter protection

Old, partly overaged clumps regain vigour if you separate sections and replant them elsewhere – in spring or autumn. If you don't cut everything back in autumn, the old foliage gives perennials good winter protection, and insects can overwinter in the stems. For early-sprouting perennials, clear the foliage only once there is no more risk of late frost – in spring it also shows you where slug-prone perennials are.

Perennial care through the year

• Spring: cut back grasses and perennials, tidy the beds, apply organic fertiliser, add new plants, divide large clumps
• Summer: support and tie in, remove spent flowers, water in dry weather, check for diseases and pests
• Autumn: add new plants, moderate cutting back, spread bark humus as protection, divide clumps, put winter protection in place
• Winter: check winter protection, cut back, spread compost soil between the clumps