How to cut back perennials and grasses

We always recommend leaving as many perennials and deciduous grasses as you can standing all through winter – for interest in the garden as well as for insects and small mammals to shelter in. Once we reach March, new growth will be starting to emerge which means it’s time to cut back the old. Here are our tips on how to do this (and as always there are a few exceptions!):

• Ornamental grasses such as Miscanthus, Calamagrostis and other deciduous varieties can be cut down to about 4-6 inches from the ground. These could have been done earlier but if, like us, you have been enjoying their structure and waftiness in the garden when there wasn’t much else to look at, you still need to cut them down now. There will likely already be new growth emerging so you may need to cut into this but don’t worry – they will soon recover and catch up.

• Evergreen grasses such as Stipa should be combed through rather than cut down, to remove the old foliage – a small hand rake is often the best tool for this. For other evergreens such as Carex (which is technically a sedge rather than a grass) it is best to remove the older/browner leaves with a small pair of snips – this can be a little painstaking but is worth it to keep them looking good!
• Perennials such as Sedum, Verbena, Nepeta (catmint) and the like should now be chopped right down to the ground to make room for new growth. We leave them standing all winter for interest, to provide structure, for the birds to feed from the seedheads and so that invertebrates can shelter in the hollow stems, but now is the time to be brave and chop them right to their bases.
• Top tip – even if your Verbena (or other perennials) are showing new growth on the old stems, you should still be brave and take them all the way down! This may seem harsh or unnecessary when they are growing higher up from existing stems, but we promise you will thank us for it. Don’t feel bad about cutting off the new growth – they need a number one haircut so that this year’s growth all comes from the base, making them stronger and more upright plants later in the year.
• More tender plants with woody stems, such as Penstemons, should not be cut back until the risk of frosts has passed, usually April or even May in colder areas. This is because they are not full hardy, and the old foliage protects them from the cold and frost.
• Evergreen perennials such as certain Kniphofia (red hot poker) need to be tided rather than cut back. As with Carex, it is just case of removing all the dead foliage – time consuming but worth it!
• After cutting back it’s a good idea to mulch to help promote growth and flowering. Mulch is a thick layer (preferably 5cm or more) of organic matter, applied all over the soil surrounding your plants. Take care not to spread it right up to the base of the plants as, when wet, this can cause the base of the plant to rot. Mulching will feed your plants, help retain water, suppress weeds and improve soil structure and fertility. We recommend using organic material such as homemade compost, well rotted manure, or fine composted bark (we like Melcourt).

Now is also a good time to divide perennials and ornamental grasses to prevent them from becoming too congested and to create some free plants!

Many perennials can be divided at pretty much any time of year as long as you water them well afterwards, but doing them now – when the soil is cool and damp – puts less stress on the plant. They will also soon be going into active growth so it’s a great time for them to be putting new roots down to re-establish themselves after splitting.

Grasses from cool climates (such as Carex, Calamagrostis, Deschampsia, Hakonechloa, Molinia and Stipa) will benefit from being divided every few years. They generally come into active growth from late winter to early spring, so this is the best time to divide them.

Grasses from warm climates (such as Miscanthus, Panicum and Pennisetum) do not need to be frequently divided.

How to divide grasses and perennials :

• Dig around the plant in one section to find the edge of the rootball, then go all the way round the plant trying to keep as much of the rootball intact as possible.
• Once lifted, shake off as much excess soil around the rootball as you can and remove any dead leaves and stems with secateurs.
• For fibrous-rooted plants (such as Japanese anemones, Asters and ornamental grasses), place two border forks back-to-back in the middle of the plant. Carefully but firmly push the forks into the rootball, levering the prongs back and forth to gently tease the roots apart. If plants are really congested you may need to use a spade (or even a knife or pruning saw) to slice through the rootball, and might be able to divide them into 3 or 4 new plants, just make sure that each section has some healthy looking buds/growth, and discard any dead or damaged looking sections.
• For fleshy-rooted plants (such as Sedum) you can use a spade to simply slice through the rootball, cutting into 2, 3 or even 4. Make sure that each section has a few healthy buds.
• Replant your newly created plants as soon as possible. If you can’t get them into the ground straight away just pot them up with some garden soil until you are ready to plant them out. Keep them well watered but not soggy, checking on them every few days. Check eventual sizes and spacings before re-planting – a division which is only 10 or 20cm wide can very quickly reach 60cm! Make sure the roots are evenly spread out in the planting hole before gently firming the plant in and watering well, As with all new plantings, keep them well watered (every 2-3 days) for at least the first few months until they establish a good root system.

I hope this helps you to keep your plants happy and healthy as well as creating some new plants for your garden. Happy splitting, and please do let me know how you get on!