Growing Herbaceous Perennials
Herbaceous perennials are the mainstay of beds and borders, providing great splashes of colour, along with form and structure.
Perennials are difficult to beat for their colour, form and interest, and there are so many to choose from you can more-or-less guarantee colour all year round. There are low-growing forms, which provide vital ground cover, to tall, imposing types providing great structure and eye-catching focal points, such as lupins and delphiniums..
Some people believe that the word herbaceous means that plants die down to ground level in autumn, coming back in spring. While many perennials do this, there are also lots of evergreens to choose from. And, of course, being perennial, they will go on flowering for many years.
How to plant perennials
Choosing plants that enjoy the conditions in your garden is the first step, but investing some care and attention at planting time and during establishment will ensure better performance for many years.
Although spring and autumn are regarded as the best times to plant, container-grown perennials can be planted all year round - just keep them well watered during dry weather.
- Make sure the soil has been prepared well with lots of planting compost and all perennial weeds have been removed.
- Ensure that the soil is loose enough to allow the roots to grow out.
- Soak the plants with water before planting.
- If necessary, if pot-grown plants look potbound, gently tease out some roots from the rootball.
- Plant with a trowel, firm the soil around the plants by hand and water in thoroughly.
- In large borders it pays to plant herbaceous perennials in groups of three or five for best effect.
The other great thing about herbaceous perennials is that they need minimal maintenance if you’ve chosen the right plants for your conditions and planted them well. But some simple routine maintenance will ensure better performance and a more attractive display.
Apply a mulch in spring, which will help prevent weed problems and maintain soil moisture levels, especially important with those plants that prefer a cool, moist root run, such as hostas and hellebores.
Some taller perennials, such as delphiniums and lupins, and those with heavy flower heads, such as peonies, usually need staking, especially in exposed areas. Supports should be put in place in spring, so that they soon become hidden by the foliage. Also, putting them in place later is more difficult and some damage may already have occurred.
Young spring growth is vulnerable to slugs and snails, so take action early in spring before damage occurs. Hostas, for example, are often attacked while the new shoots are still below ground level and as they unfurl.
Keep weeds under control - not only do they look unsightly, but also compete for space, light, food and water.
Keep young plants well watered and established plants may need watering during prolonged dry periods.
Giving the plants a good feed with a continuous release feed in spring will improve growth and flowering.
Deadheading faded flowers keeps plants tidy and can lead to further flushes of flowers later in the year.
In autumn, cut back dead and dying foliage and flower stems, unless you want them for winter effect, such as the flower heads of sedums or ornamental grasses. In cold areas and with not totally hardy plants, cutting back is best left until spring, as the top growth provides some protection against the cold.
Division and propagation
After a few years some perennials will have grown into large clumps, and eventually the mass of congested roots can mean reduced vigour, dying out in the centre, less flowering and problems with disease, such as powdery mildew. More invasive perennials will also start growing into their neighbours.
At this time, you will need to lift and divide the plants.Not only will this improve performance, but you’ll also have a greater number of plants, which can either be planted elsewhere in the garden or given away.
- Divide perennials during their dormant season, usually between late autumn and early spring.
- Dig up the clump and divide the roots by teasing the clump into separate pieces by hand, with a hand fork, or for large clumps, two garden forks used back to back.
- Plants with fleshy roots are usually best divided with a sharp knife - each section should have at least three to five growth buds.
- The youngest, outermost portions are the most vigorous; the central section is the oldest and should be discarded.
- Make sure that each piece has more roots than top growth to ensure good re-establishment.