Whatever the weather is doing at the moment, March is traditionally the time to divide herbaceous plants. Most herbaceous plants will soon be bursting into growth and if you divide them into sections to replant now they will quickly recover, grow and be in bloom.
But before we get started we need to understand why we are dividing them.
We grow a huge variety of plants in our gardens and they do not all grow in the same way. Peonies, for example, have thick, deep roots and do not move in the soil – they just get bigger and better.
To maintain health
Other plants, such as monarda, perennial sunflowers, asters and Siberian iris form new shoots at the edge of the clump and, being in fresh soil, these grow most vigorously. The inner part of the clump, shaded and deprived of nutrients, slowly dies so you end up with a ring of healthy growth. These are the plants that need to be divided every three to five years to maintain their vigour. Asters need more frequent division.
To make more plants
You may want to divide your plants so you have more of them. You may have bought a nice daylily or hosta and would like three or five of them. Then divide them now.
To move them
You may have planted them too closely and need to move them or perhaps some shrubs have crowded them.
To control weeds
Perhaps you have problems with weeds like ground elder in the clump. You can lift the plant and extract the weeds and divide the plant before replanting in weed-free ground.
Easy plants such as hardy geraniums can be dug up and initially cut in half with a spade. Then get in to the clump and you can cut the plant into sections with a knife. (you can see how wet my garden is this spring)
Some plants have huge roots – such as established clumps of daylilies. It may be easier to just cut off some sections from the outside and refill the holes with fresh compost. (this is Centaurea montana – perennial cornflower)
Before replanting, fork in some garden compost or planting compost to improve the soil. (this was actually taken when dividing daylillies in autumn)
Whatever the weather, always water in the newly planted pieces. It settles the soil around the roots and prevents air pockets in the soil which can cause roots to dry out and die.
You can often divide herbaceous plants as soon as you buy them! If they are stock from last year they will have increased in the pots and you may be able to divide them. The pieces will be smaller than if dividing garden plants so it is often best to pot the pieces so they grow on for a few months before putting them in the garden.
You rarely need to divide peonies but there is no reason why you can’t. You may want to move them if they are being shaded, which results in poor flowering. Cut the crown carefully into sections, making sure each piece has several shoots. Replant immediately. It is important that they are not planted too deeply. If the top of the crown is more than 3cm below the soil surface it will reduce blooming. You do not usually need to divide or move peonies but, if you need to, do not be afraid!
Weekly reminders
Buy and sprout (chit) seed potatoes
Start the seasonal war on slugs and snails, in whatever way you prefer
Plant trees and shrubs. There is just about time to plant bare-root shrubs including hedges
It is just about time to start sowing tender veg and flowers in the greenhouse. Antirrhinums are generally among the first but if you have a warm propagator you can sow petunias, pelargoniums and impatiens now. More on sowing next week