5 plants to divide in August – experts say it's the perfect time to lift and split these popular varieties to get free plants next spring

August is here, and with it comes a gardening job that's going to give you more beautiful plants without costing a penny.

'This month is one of the better times to lift and split certain perennials, especially anything that has become congested or is flowering less freely than it used to,' says Julian Palphramand, head of plants at British Garden Centres.

There are some other great reasons to divide plants this month too – it stops overcrowding and gives tired varieties a new lease of life, and doing it this month ensures the ground is still warm enough for the plants to get established before winter. We look at which plants you should start dividing below and how.

1. Irises

'Irises are the obvious one and respond well to being divided once they’ve finished flowering and before growth slows down,' Julian adds.

So what's the best way to do it? 'Always pick a cool day,' advises Julian, 'Replant straight away and water them properly afterwards. It’s really about giving the plant room to breathe again; if a perennial has started to suffer, that’s often your cue.'

If you love irises, then there are some lovely colours to choose from. First up that we love is Iris Orange Harvest, from £9.99 at Thompson & Morgan, and it's guaranteed to flower in the first year.

The Beverly Sills variety is a stunner too, with its delicate coral pink flowers, from £4.99 at J.Parkers.

2. Lady's Mantle

This is one variety that most of us love with its vibrant lime green flowers and distinct look. We asked Lucie Bradley, gardening and greenhouse expert at Easy Garden Irrigation, about how to divide it.

'The best time to divide is when the centre of the clumps becomes old and woody, and there are fewer blooms. Dividing it will refresh it and prevent the older middle section from dying. Use a spade or fork to dig about 5 to 7cm deep around the base of the plant and carefully lift the root ball from the ground, using the foliage to help handle it from the ground.'

Once you've lifted it out, shake off the excess soil and trim back the foliage, removing old flower stems and cutting back the older, larger leaves, but keep the younger ones, says Lucie. 'This helps when it has been divided and replanted to concentrate its energy on establishing its root system and helps reduce water loss through the foliage. Then cut through the root ball and divide it into sections and replant immediately.'

Lady's Mantle is a great perennial for its colour and coverage. You can buy it in one litre pots for £7.99 from Gardening Express.

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3. Hostas

Hostas are an eye-catching variety, and they can get to the point where they need to be divided. This stops them from spreading and allows you to propagate the new plants.

If the centre of your clump is looking a bit tired and the plant is too crowded, these are your signs. They are prone to outgrowing the position you originally planted them in and should be divided between year three and year five.

How do you divide hostas? If the hosta is small, you can divide by hand; if not, then find a central point and simply cut through with a knife, remove any damaged foliage and give them a drink in a bucket of water before replanting.

J.Parkers sells a hosta mix, pack of five first-grade loose roots for £7.99, or check out the hosta patriot plantain lily from Amazon, £10.99 for a 9cm pot; it's a more traditional-looking variety.

4. Daylilies

Daylilies are kind of what their name suggests – they only last for 24 hours; they are also tough cookies, and their blooms are edible.

Richard Barker, horticultural expert and commercial director of LBS Horticulture, explains, 'Daylilies can be divided in early spring or late summer once they have finished flowering. Use a spade to lift clumps out of the ground, and select young growth from around the edges of the clump. Try to break off crowns by hand, ensuring each has roots and shoots.'

When you replant, make sure you fork the soil around each one and give them a good water.

If you like the idea of daylilies, you can buy them in various pretty colours. Crocus's Hemerocallis collection consists of three bare roots, £23.95, and you get Strawberry Candy, Canadian Border Patrol and Olive Bailey Langdon.

Suttons sell three featuring yellow, red and orange varieties called Stella Trio for £19.99, and you get 9cm potted plants ready to be planted.

5. Oriental poppies

Poppies bring so much joy, and they create a fabulous statement from late spring to early summer – and they are quite consistent for around five years.

'Once your plants are over 5 years old, they are likely to be past their peak, with clumps becoming large and woody,' explains Lucie. 'At this age it’s worth dividing up your poppies, and August is the perfect time as they are coming to the end of their summer dormancy and new green basal foliage will start to be produced as temperatures cool.'

Poppies have long tap roots that can each 30cm or deeper into the ground; this means they can be challenging to divide.

'To avoid damaging these long roots, you will need to carefully dig a wide, deep circle around the perennial so that you can lift out the entire root ball, as damaging the tap roots can cause new divided plants to fail. Once you have successfully removed the roots from the ground, use a clean, sharp knife or pruning shears to cut vertically through the roots, making sure to include one ‘eye’ and a piece of tap root in each divided part,' says Lucie.

Make sure you've pre-prepared where they're going as the roots can dry out quickly.
You can buy three bare root plants, each a different variety of oriental poppies from Dobies for £16.49 (currently on offer). The varieties are Beauty of Livermore, Victoria Louise and Queen Alexandra.

For a single variety, check out Farmer Gracy's Perry's White, which is simply stunning and is priced at £5.90 for one bare root.

Go and have a walk around your garden to see if the varieties mentioned above are looking a little crowded, if so, have a go at dividing them and good luck!