Best Tips For Growing Herbaceous Perennials

Follow our hints and tips for spectacular colour from spring to autumn

Scabious 'Pink Mist' and Raphiolepsis 'Crimson Coates'

Planting

• There are plants available for almost any situation, but they prefer well-draining, moisture-retentive soil in full sun and shelter from strong winds.
• Check the plant label for the eventual spread and plant to this distance. If you want them to knit together quicker plant a little closer, but they will need lifting and splitting sooner and if they don’t have good airflow they are more susceptible to mildew.
• Don’t plant too close together as they will be fighting over water and nutrients.
• Prepare the ground well by digging in well-rotted farmyard manure; and good quality peat-free compost if you have sandy soil.
• Dig the hole just a little larger than the pot it is already in and loosen the soil around the sides of the hole.
• Add a little balanced fertiliser, such as Growmore, or blood, fish and bone into the planting hole.
• Plant bare rooted as soon as they arrive in spring or autumn; if this is not possible keep them somewhere cool and out of the sun and make sure the roots are kept damp.
• Container grown plants can be planted at any time provided the ground is not frozen or waterlogged.
• Water the plant before taking out of the pot as dry roots often stick to the sides of the pot and can be damaged if ripped out.
• If the plant is pot-bound (pot stuffed full of roots) tease them out before planting.
• Plant to the same depth as they are in the pot.
• Once planted firm in with your toes.
• Water in, even if rain is forecast, this settles the soil around the roots.
• Plant in groups of 3 or 5 rather than single specimens as that can look very messy; unless it is a large specimen, such as Cynara cardunculus (Cardoon) or Crambe cordifolia (Flowering Sea Kale).

Sizergh Castle

Aftercare

• Make sure you water well the first year after planting until the roots have spread out. This applies even if the plant is a drought tolerant species.
• If the ground is well prepared before planting a new plant shouldn’t need feeding for a couple of years.
• In spring feed with a balanced fertiliser, water well and mulch; this keeps in the moisture and deters weed germination.
• Stake tall plants in early spring with bought supports or make your own from short pea sticks or woven branches.
• Large clumps need to be divided every few years otherwise they lose vigour and start producing smaller and smaller flowers and some die out in the centre of the clump.
• After splitting plant large pieces straight into the border; smaller pieces can be potted up and placed in a cold frame until they are large enough to go into the border.
• Split congested clumps in early spring before they start into active growth.
• Have the new planting hole or pot of compost ready so that the new plants’ roots are not exposed to drying air longer than necessary.
• Dig up the whole clump, taking care not to damage the roots, by digging a little away from the plant. Shake off as much soil as possible so that you can see where to split them.
• Some produce small buds, divide these into smaller pieces containing about 3 buds.
• Large fleshy roots can be divided by slicing into pieces with a sharp spade.
• Split fibrous rooted plants by placing 2 forks back to back in the centre of the plant and easing apart.
• Some produce individual plantlets and these can just be cut off.
• Bearded iris need dividing as soon as they have flowered in summer; dig up and cut into pieces each with at least 3 eyes. Cut off the spent flower spike and cut back the foliage to about 15cm (6”) and re-plant.
• Plants which form corms, such as crocosmia, can be split up into individual corms.
• Make sure each piece of new plant has plenty of roots.
• Discard the centre of the plant which has stopped producing any flowers.
• Keep on top of weeds; a little and often is a lot easier then dealing with an invasion.  
• Cut off the dead vegetation in spring rather than autumn as it will provide some protection for the crown over winter, and a lot of dried vegetation can be sprayed with metallic paint and used for Christmas decorations.

Levens Hall

Problems

• Slugs and snails will be a problem in spring, all that soft new growth is irresistible, so you will have to be vigilant and put down deterrents or else go out at night with a torch and pick them off.
• Rabbits are also a problem with new growth and unfortunately these are a lot harder to deter than slugs; you may have to put rings of chicken wire around susceptible plants.
• Mildew can be a problem in herbaceous borders so keep them well watered and maintain a good airflow around the plants. At the first signs spray with a fungicide to prevent it spreading, but if there is a heavy attack you will either have to cut off the plant at the base or just live with it. Some species do have more resistant varieties, so consider planting one of these instead of the old favourite.
• Cutting the plant back down to near the base after it has flowered should, in most cases, produce a second flush of flowers in late summer/early autumn.

For more gardening advice get in touch with our team here in the Outdoor Plant department.