One of the recent themes of our gardening conversations here has been perennials. Perennial gardening and herbaceous borders are our current challenge, albeit one that may take us a decade or two to get to grips with. (Have I mentioned that we take the long term view regarding gardens and gardening?)

New Zealanders tend to be exceptionally good at creating quick impact, pretty tree and shrub gardens. Avenues of cherry trees, hedges of camellias, flowering daphnes, roses and the like – all flourish in our equable climate, grow quickly, have almost instant impact and are relatively easy care. Where perennials are used, they tend to be part of mixed borders to add seasonal flowers and foliage. Plants like irises, polyanthus, hostas and more recently clivias and that other fashion plant of today, bromeliads, are part of the repertoire of most gardeners.

Mark and I had a passing debate as to whether or not a bromeliad is a perennial so I went in search of a definition of what constitutes a perennial. We all know of annuals – plant them at the start of the season and they grow rapidly, flower profusely, set seed and die. Pansies and petunias and the like. By definition, perennials are per (through) and annus (year) – so they are plants which last through the years, rather than being one season wonders. In New Zealand the term perennial is commonly used to describe plants which are clump forming and don’t have woody stems and branches. Sometimes they are called herbaceous (leafy and non-woody) perennials, and they take in a wide range of plants.

When the English talk about herbaceous borders, they commonly refer to the use of deciduous perennials which form clumps below the ground and put on a huge amount of leafy growth and flowers in spring and summer, then die back in autumn and go to sleep for winter. In that cold climate, gardeners tend to be forced indoors and go to sleep for winter too, so they don’t mind large areas of garden which are bare for several months of the year. It is not a style of gardening that has ever really caught on in this country and I think that has a lot to do with the fact that our winters are mild and we are not housebound for months with very short daylight hours so we expect our gardens to look pretty well furnished all year round.

But we are enormously impressed by the English tradition of herbaceous gardening and the skills which they bring to creating good summer gardens using members of the perennial family. I have seen good perennial borders in Dunedin Botanic Gardens but generally, it is the mixed border that New Zealanders do well – using woody plants to give a framework and then underplanting with perennials to give layers of foliage and flowers and to extend the season of the border.

If you think about it, in this country we have very pretty spring gardens. The majority of trees and shrubs mass flower in spring. But the summer garden is a challenge and one in which we do not shine. True we can grow splendid hydrangeas but there are only so many hydrangeas one wants in the garden. Certain other plant groups will peak in summer. Lilies are big for us in our garden. Others use annuals. But that English summer border which is fresh and vibrant and full of contrasting foliage and riots of flowers has not been highly sought after here.

There are reasons and the first is that perennials are actually quite a bit more work than woody trees and shrubs. We also tend to have narrow borders and those summer gardens don’t lend themselves to borders which are a mean 80cm wide, or even a couple of metres. A proper perennial border needs space – at least three metres and preferably five in width. Add in our winds and our torrential downpours, both of which can flatten the herbaceous border if the staking and support are not up to it. Many plants need quite high levels of support to keep them from falling over. To maximise flowering, the plants need deadheading. And lots of feeding and mulching (it takes a lot of energy for a plant to put on all that growth and flowering afresh every year). And they need to be lifted and divided or thinned and to have well cultivated soil. It is all much more labour intensive than the once a year dead heading round of rhododendrons, the annual prune of hydrangeas, or the occasional shaping and pruning of a camellia.

Mark has a yen to have proper English styled herbaceous borders. You may think that in a garden which covers around seven or eight acres, we would have plenty of space to establish that. Alas no. All available areas are already planted and the herbaceous border needs flat or near flat land and plenty of space, shelter from the wind and full sun. The only suitable area he can spy is where we have our plant nursery and as we are neither rich enough or old enough yet to abandon the need to earn a living, all he can do is look out from the upstairs window at the area he would like to claim. So that plan is on hold for the time being.

But in the meantime, we have been applying ourselves to learning how to better handle perennials. We have not done them particularly well to date, being of the plant and leave brigade of gardeners. We will groom the plants, feed them and mulch them as part of the garden maintenance regime, but the whole difference with perennials as compared to woody plants, is that if you lift and divide them and cultivate the soil, they will reward you tenfold. Whereas if you just leave them for years, they will start to look tired and congested and in some cases get smaller and less rewarding over time. So we are on a lift and divide campaign at the moment. It may take us several years to catch up with the backlog.

We have friends with a garden which has large perennial borders around a pond. I can remember when it looked amazing. Now it looks cramped, tired and tatty. Every plant desperately needs to be lifted and divided and the entire area needs to be replanted. The rewarding thing about perennials, is that if it is done now, the whole area will look fresh and splendid this spring and summer. It is a really quick return on labour and effort.

We had an old time experienced horticulturist staying with us over the weekend. Inevitably our conversation turned to perennial gardening (you can tell it is much on our minds at the moment). He instantly came out with two pieces of old wisdom which were new to us. The first is to avoid over fertilising. That encourages too much quick growth and the plants won’t hold up. A stout, sturdy plant is what is needed. Compost is good, but keep the nitrogen levels lower. Avoid high nitrogen artificial fertilisers. And if you are not lifting and dividing every two years or so, you should at least get out each winter and reduce every clump to about seven or nine growing tips. This avoids congestion and the remaining growing tips will be stronger as a result.

But dear Reader, if you are inspired to look at your clumping plants in the garden, from now until early spring is the time to get out there, dig them up, split them into smaller plants and replant only some of them in the same place. Which may give you an entirely new problem as to what to do with the leftovers.