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HOW TO GROW PERENNIALS 

Perennials are plants that last for three seasons or more, some die down in winter and emerge again from their rootstock in spring to flower in summer and winter. They are longer lasting plants than seasonal annuals. Herbaceous borders are grown using mainly perennial flowering plants. The flowering season is largely during late spring, extending through summer and into autumn. 

Some exceptions to this rule prevail like winter flowering Kniphofias and Helleborus. Many plants classified as perennials form clumps that grow increasingly larger. They need to be dug up and divided into smaller plants before being re-planted. This practice is best carried out either in autumn or early spring.

PLANTING PROCEDURES

– Prepare the soil by digging over deeply with garden fork
– Add superphosphate or bone meal as root stimulating fertiliser and good compost at
recommended rates
– Dig into soil and mix thoroughly
– Rake soil to correct level
– Remove the plant from pot or nursery bag
– Carefully untangle some of the matted roots where necessary
– Dig a hole large enough to accommodate the root ball comfortably
– Place plant in hole and fill in around the root ball and firm soil down gently
– Make sure the plant is buried at the same level as it was growing in pot or bag
– Once planting is complete water well to settle in

FERTILISING AND CARE

– Apply a layer of mulch (pine bark is best) on the surface of the soil around the perennials to
supress weed growth and reduce watering
– Regular fertilising with a balanced granular plant food every 4 to 6 weeks from spring to
autumn ensures healthy growth – a 3:1:5 or 5:1:5 formula is ideal
– Pinch out the growth tips of tall, lanky plants to encourage basal branching (only applies to
certain plants)
– Dead head spent flowers by removing the flower stalk and developing seed capsule
– Prune back any plants that get straggly or untidy
– Cut back spent perennials in late autumn
– Split or divide overgrown clumps immediately after this
– Apply a new layer of mulch after the autumn clean up

PESTS AND DISEASES

– Aphids gather on the soft new growth tips and suck the sap out of the plant – control with
general purpose insecticide
– Caterpillars, beetles and grasshoppers chew the leaves – treat with a systemic insecticide
(only suitable for use on non-edibles)
– Red spider mites are a problem on some plants, especially in summer – use a suitable
miticide
– Fungal diseases like mildew and rust on the leaves – spray with a broad spectrum fungicide
– Cutworms chew seedlings off at ground level – apply Cutworm bait immediately after
planting or drench newly planted seedlings with general insecticide
– Snails and slugs are nocturnal pests that eat the lush young leaves – apply snail bait at
regular intervals especially early spring

GARDEN USES

– Ideal for planting in mixed herbaceous borders
– Useful for filling space amongst shrubs and roses
– Some work well in mixed pot plantings
– Clump forming types are used as groundcover in mass plantings or to stabilise banks
– Many perennials are good cut flowers

SUMMARY

1. Select the correct plants for your purpose and growing conditions
2. Prepare the planting soil well with added nutrients
3. Fertilise heavily during the spring and summer growing season
4. Check regularly for pests and diseases and treat accordingly
5. Prune back spent flowering stems at the correct time