Diarmuid Gavin: The plants that keep on giving
With the right preparation, perennials will perform year after year
After a winter largely devoid of colour in our gardens, we really look forward to the weather warming up and wave after wave of blossoms arriving to brighten our plots from now through to the autumn. At the moment, we're luxuriating in spring-flowering bulbs and beautiful Magnolia trees with their cup-like flowering. But looking ahead, the flowers that many of us will enjoy in our borders are often perennials. Think of summer gardens and you begin to conjure up images of beds packed with lupins, delphiniums, Oriental poppies, penstemons and the likes.
In gardening talk, 'perennials' is a term for flowering plants which don't produce a woody stem but do come back year after year. Rather than building up that woody branch and stem network, they often loose their foliage in late summer to early autumn only for fresh growth to appear the following spring.
We tend to purchase these plants in garden centres and at flower shows when they are in bloom, but what should we know about them? And how can we create a complementary collection of perennials to fill out our borders?
First - as with all planting schemes but especially when using the type of plants that will produce huge amounts of lush growth and flower every year - prepare the ground well. It's your big opportunity to create a great foundation to anchor the plants and to provide the roots and shoots with everything they need.
Loosen the soil, remove stones, and add organic matter: this can be composted house- and garden waste, or bags of well-rotted manure. It's much easier to properly prepare the soil before you start planting, rather than trying to repair ill-performing soil in a couple of years' time.
Most perennials prefer a pH of about 6.5, although, some prefer more alkaline or acidic soil. If you have trouble with a particular plant, check its pH requirements and the pH level of the soil in your flower garden. If your plants look stressed during the growing season, or if you see disease or insect damage, feed them with a quick-release organic fertiliser. If a plant performs poorly, try moving it to a different location. If it still is not happy, give it away or send it to the compost pile.
Most perennials can be divided in early spring every couple of years when new growth is only a few inches high. If you miss your chance in the spring, wait until autumn. Irises are the one major exception to this rule: they should be transplanted in early summer, right after they have bloomed.
When designing a perennial garden think about how you'll get access to your plants to stake, deadhead, or divide them. Paving slabs can be used as stepping stones within the garden, or set out a walkway of forest bark. A walkway created at the back of a border will be hidden during the growing season, but will make the bed accessible for spring and autumn maintenance.
Read the labels on the plants and discover what sizes they will grow to. Position taller species to the back and place lower growers at their feet or to the front. Choose different species to do different jobs: soft mounds of nepeta, alchemilla and hardy geraniums are brilliant for filling in gaps and edging the front of the border.
Use spires of salvias (pictured), verbascum and iris to create vertical interest points throughout and floaty perennials like verbena, cow parsley and fennel to soften the look.
Try to include plants that will flower across the seasons - for spring, aquilegias, primroses and Solomon's seal, and then for late summer and autumn, flowering plants such as rudbeckias, heleniums, chrysanthemums, crocosmia and sedums.
Keep an eye on the colours so you build a harmonious arrangement. Rather than buying single plants of lots of species, choose your top 10 and buy a few of each so can you repeat patterns and knit your scheme together.
If you start this year, your plants will bulk up over the years and combine to form a mature and artistic arrangement.
Keep newly transplanted perennials well watered for the first few weeks. Water deeply to saturate the entire root ball and establish good contact between the roots and the surrounding soil.