Tender herbaceous

Perennials are any plant living for at least three years. The term is also commonly used for herbaceous perennials which grow for many years (To compare: annual = one year, biennial = two years).

Rhizomes are creeping swollen root-like structures that are actually adapted stems. Roots, stems with leaves and flowers are produced along its length. See plants such as Anemone nemorosa, bamboo, canna, border iris.

rhizomes

Dormancy refers to a period of inactivity in plants, during which they slow down or stop their growth, conserving energy and resources. This is a natural process that helps them survive harsh conditions, such as winter or drought. Dormancy in seeds is a mechanism that prevents them germinating until environmental conditions are favourable for growth.

dormant

In milder areas of the UK and in sheltered, well-drained, parts of the garden, it may be possible to cut back the tops of tender plants, leave them in the ground and cover them with a thick

Mulch is a layer of material, at least 5cm (2in) thick, applied to the soil surface in late autumn to late winter (Nov-Feb). It is used to provide frost protection, improve plant growth by adding nutrients or increasing organic matter content, reducing water loss from the soil, for decorative purposes and suppressing weeds. Examples include well-rotted garden compost and manure, chipped bark, gravel, grit and slate chippings.

Perennials are plants that live for multiple years. They come in all shapes and sizes and fill our gardens with colourful flowers and ornamental foliage. Many are hardy and can survive outdoors all year round, while less hardy types need protection over winter. The term herbaceous perennial is used to describe long-lived plants without a permanent woody structure (they die back to ground level each autumn), distinguishing them from trees, shrubs and sub-shrubs.

perennials

Tender plants need protection at the first warning of frost, usually between September and November.

Specific cultivation practices are also used to protect plants from winter damage, and these are started from mid-summer onwards. See our advice on preventing winter damage for further detail.

Cannas, dahlias and pelargoniums (commonly known as geraniums) can be lifted and stored in a semi-dormant state over winter. Where lifting and storing are not necessary, then thick, dry mulch over the crown of non-woody plants may be all that is needed for winter protection.

See our advice on pelargoniums for information on overwintering these popular garden plants.

Lifting plants

Cannas are lifted after the foliage has been blackened by frost:

• Cut back the stems 5cm (2in) from the base. These stems can be composted
• Use a fork to prise the plants out of the soil, taking care not to damage the roots or fleshy rhizomes
• Remove debris and loose soil
• Store them in trays of sand, coir or vermiculite, with the crown of the plant (where the stems join the roots) just showing
• Keep them just moist in a cold, frost-free greenhouse or conservatory
• Container-grown plants can be stored in their pots after cutting back

Dahlias are also lifted once the foliage has been blackened by the first frost:

• Cut off the old flowering stems 5cm (2in) from the base and trim away any thin roots. These stems can be composted
• Use a fork to prise the plants out of the soil, taking care not to damage, cut or bruise the tubers, as this can lead to rots developing in storage
• Remove the soil from the tubers by hand. Position them upside down in a cool place for a few weeks to dry off
• Label cultivars and bury in trays or wooden boxes filled with dry sand, soil or compost, leaving only the old flower stalks exposed
• Place the trays in a cool but frost free place, such as a garage attached to a house or a shed

Begonia tubers are lifted and stored in the same way as dahlias. Gladiolus corms can be lifted and stored like bulbs. See our bulbs page for further information on lifting and storing bulbs.

Protecting plants with mulch

Where lifting and storing are not necessary, a thick, dry mulch can be used for protection. In mild areas, cannas and dahlias can be overwintered like this, as can deciduous Agapanthus (those that lose their leaves in winter) and globe artichokes. The young shoots of lilies can be mulched to protect them from late spring frosts. The tender shrub Melianthus major can be cut back to ground level and then mulched for winter protection.

Suitable mulching materials include straw, garden compost, chipped bark or well-rotted manure. See our advice on mulches and mulching for further ideas.

Tender plants that can not be lifted and stored

These need to be wrapped and protected in situ. See our advice on overwintering tender plants under wraps for further information.

Rots can develop in stored tubers, corms and rhizomes. Keeping them dry and well ventilated is important.

Plants protected under mulch may come into growth and flower a little later than those lifted, stored and replanted in spring.