Your perennial planting masterclass
Now’s the ideal time to start your new borders
There’s lots of time to dig the soil, add compost and start planning your plantings, but first it's important to get rid of perennial weeds, as it's extremely difficult to get rid of them once it’s all planted. Bindweed will smother and ground elder and couch grass will get into clumps. If possible, dig over the soil and remove weeds or spray them with a glyphosatebased weedkiller. There’s just time to use these effectively, though some perennial weeds will need more than one application.
Good soil preparation is important, since perennials may be in the soil for many years. They vary in the time they’ll grow without needing dividing and replanting; Michaelmas daisies are best replanted every one or two years, Siberian iris can be left for five years and peonies can be left for decades. There are perennials for any soil but all will benefit if the soil's well dug and improved by adding organic matter such as well-rotted manure or garden compost. Clay soils will benefit from adding coarse sand or grit.
Soil that's very dry in summer will suit silver-leaved plants and there are a few plants that can even cope with wet soils, though the choice will be limited.
Getting plants
Garden centres tend to stock plants when they’re in season, so there may not be a large choice at the moment. However, if there’s stock from earlier in the year it will have grown and be good value because it may be large enough to divide – you could get three young divisions from a potful.
For the widest choice it’s worth buying plants by mail order. These may be bare-rooted but these will grow well if planted when dormant, from now until March. When the plants arrive, don’t allow them to dry out and if your soil isn’t ready for planting you should pot them, if only temporarily.
You may be able to get plants from friends but be careful that they don’t contain weeds. If in doubt, search through the roots or grow them in pots first so that any weeds aren’t introduced to your borders. Also bear in mind that the plants most often given away are those that are vigorous or even invasive – be warned!
Dividing your own
It’s easy to make more plants by dividing existing stock – the young plants will be identical to the parent. Most can be divided any time between now and March. Plants that are slightly tender, such as agapanthus and all grasses, are best left until March when the plants are starting to make new growth, so will quickly establish. Dig up the clump first. If the clumps are very large, dig around them to remove soil, then push a spade into the centre and extract sections. Shake as much soil off the clump as possible, then cut it into sections with a knife. This is easier than attempting to break it into sections with a fork. Don’t allow the roots to dry out before replanting.
Growing from seed
Perennials vary in how easy they are to grow from seed. Most don’t come true from seed but a good range can be raised easily and cheaply from this way. Lupins, delphiniums and aquilegias are especially easy and well worth the effort. Some perennials will flower in the first year if sown in heat early in the year. Agastache, achillea, Iceland poppies, some foxgloves, echinacea, diascia, coreopsis, gaillardias, hollyhocks, geums and dianthus are all useful plants that will fill borders for minimum cost.
Designing
The good old plan of putting taller plants at the back and shorter ones at the front is a good basic rule. If you want to have three rows of plants your border will have to be at least 1.5m (5ft) wide. Then you’ll have to decide if you want contrasting colours or complementary ones. Take into account flowering times too, or your careful pairing may not be effective. Make good use of colourful foliage and consider plant shapes and textures as well as just colour. Remember that if you make a combination you don’t like you can move plants the following autumn.
Spacing
When it comes to spacing plants, you often have to compromise between getting a full effect with lots of plants or having a gappy effect for a year or two. Unless plants are very big or small, they should be spaced between 60-90cm (2-3ft) apart. Unlike shrubs, which won’t be disturbed once planted, herbaceous plants can be lifted and divided so if you can only afford one plant, you can lift it and divide it into three after a year to make a clump. In the first year you can fill in the gaps between immature plants with annuals or biennials to make a better display. There’s no reason why perennials can’t be planted between shrubs or used in borders with roses and annuals. There's such a wide variety of plants for sun or shade that you’ll find the ideal plant for any situation.
What to do in future
Once planted, herbaceous plants won’t need a lot of attention for a few years. Weeding is the most regular activity, at least until the plants get big enough to shade the soil. Most will benefit from feeding in spring and being mulched – to keep in soil moisture and prevent weeds. They’ll need cutting back in winter. It’s best to do some of this in late autumn, especially if you have spring bulbs planted. After three or four years you may have to divide and replant some plants.