How to Look After Herbaceous Perennials
Herbaceous plants are mostly clump-forming. They have strong underground storage organs which survive over winter whilst the soft shoots above-ground die back. Herbaceous plants are either grown in mixed borders with trees and shrubs, or they are grown in borders planted with only herbaceous plants.
Looking After Herbaceous Perennials:
The maintenance operations that need to be done each year to maintain a herbaceous border are: division, staking, weed control, dead-heading, feeding, mulching, pruning and cutting.
At the end of the season, old flower stems are cut back down to the ground. This gives room for the new shoots to emerge. Some plants are left over winter because they offer some interesting winter structure. These must be cut back as new shoots emerge the following spring.
Weeds can be a big problem amongst herbaceous plants as they will grow up through the clumps and are not easily re-moved without damaging the plant. Herbicides cannot be used as, unless the weeds are very carefully spot-treated, they will damage herbaceous growth. Hand-weeding is done throughout the summer. If a weed problem becomes very bad, the clumps are lifted out of the ground. The weeds can then be cleared from amongst the roots and from the ground before replanting.
Herbaceous plants in the border need nutritious ground. The best source of this is composted waste or rotted manure. However, this sometimes introduces more weed seeds. Fertilisers applied in the spring will improve plant growth.
Mulching herbaceous plants in the spring helps to conserve water and suppress weed growth. The best materials for mulching are composted garden waste, leaf mould or well-rotted manure. These will also add nutrients to the ground. Bark or composted bark can also be used. Fresh manure should not be used as it will scorch young, soft shoots.
In the spring, as shoots emerge, stakes should be put in place ready to support long flowering stems. The best stakes are old, woody prunings, as these look very natural. Canes and plant rings can also be used but these may be visible through the season. Stakes are needed more on a border where light does not penetrate all around the plant.
Removing the flower heads as they mature will encourage the plant to produce more flowers and extend the flowering period. In most cases, this is done to individual flower stems with secateurs. Some plants can be cut back with shears after flowering to encourage more growth and a repeat flush of flowers. Crowded stems can be pinched right out before flowering to thin the number of flowers if necessary.
In spring or autumn, large clumps will need to be lifted and divided into smaller plants, which can then be replanted. The frequency with which this is done will depend on the vigour of the plant, but is normally every 3 to 4 years. Fibrous-rooted perennials are lifted and split apart with two forks back-to-back. Early-flowering plants are divided in the autumn and late-flowering plants are divided in the spring. Fleshy-rooted plants, such as hostas, are lifted and split apart with a spade or a knife in the spring. The older part in the middle is discarded ,and the younger from the outside is replanted.