Garden Guru: Spreading out

Clipping, as with these Ionocera domes, can help individuals from being too cosy with each other. Photo / Supplied

It's a perennial joke in our house that whenever we go away my wife just throws a couple of tops into a small hold-all, but it could take a whole village of sherpas to shift the mountain of T-shirts and jeans that I can't seem to live without.

Whether it's clothes in suitcases, food at a smorgasbord, or plants in garden beds, I always try to pack in too much. And at this time of year when we are busy planting and moving things about the garden, shuffling the pack, I'd guess that I'm not alone in my habit.

After several days clearing an overgrown garden for a gardening friend who had just moved, I was surprised at the extent to which she underestimated how much room her new acquisitions would need, despite her passion for plants.

When you love plants you will always tend to be far too optimistic as to how much you can shoehorn in.

Landscapers also tend to plan for two times the number of plants than are really needed. The motivation is no doubt to achieve instant effect but, as well as being expensive, it is to the detriment of the plants themselves most of which need light and air to circulate around them if they are to look healthy and happy.

It's impossible to predict just how wide a plant might get, or how fast that will take. That would be like looking at a baby and predicting what line of work he might eventually take up.

If you are lucky, the label on a plant you buy will give an indication of height. But it rarely gives width and never speed (plants, not babies that is). So how do you avoid over-planting and having to move everything about in a few years' time?

Some homework with a good book is a good place to start, but after that check out how mature specimens are doing in neighbours' gardens and consider the type of plant. Groundcovers - like politicians - will go on forever unless you wade in with the shears and curb their enthusiasm.

So with a vigorous spreader, such as a low growing coprosma, the question of how many you will need depends on how quickly you want the ground smothered.

It's often said to never plant singly but always in groups of three or five but with groundcovers the rules need not apply because a single specimen will soon do the job of a whole team.

Other plants, however, sit for years with their arms folded and go nowhere fast. Pinks, or dianthus, hemerocallis and liriopes make smug little clumps and if you try to make a 5m drift with just three your efforts will look mean, like jam and cream spread too thinly on a scone. Clumping grasses like tall miscanthus or small native carex are similar - these self-contained upright shapes nearly always look best in groups. A guide is to arrange them rather how you would find family or friends scattered around the barbecue on a summer's evening - the women zigzagging two and fro, a sulking teenager huddled in a corner and four blokes clustered around a blackening sausage.

You don't want specimens at arm's length with big, impersonal gaps between but neither do you want everything packed together awkwardly.

With architectural plants such as aloes, astelia and cabbage trees, the arrangement is especially important as they are so dominating. Unless you are doing high formality, aim to weave them along a flower bed informally but relating - as if they are holding hands.

Shrubs and trees are often the most expensive elements you will buy for the garden and the longest lived, so get their spacing right first. Spread them on the thin side to allow full development and plug the gaps with cheaper and faster-growing ephemerals. A packet of annual seed will instantly give you interest in the gaps for a year or two but perennials are a more robust choice. Bulbs are ideal quick fillers too and many will happily shine even when they become engulfed by shrubs.

As a guide, assume taller, head-height shrubs will bulge to 1.5m to 2m - think of them as wardrobes and allow similar space.

Waist-high shrubs should also be arranged generously. Never believe those pictures you see on garden-centre labels for a hebe, cistus or a lavender - such seemingly cute bun-shaped domes should be grouped as if they will reach the size of armchairs (1m to 1.5m spread).

Let them spread their wings and they will sing for you, rather than looking like they have just squeezed off the plane after a 24-hour budget flight to nowheresville.

Could do this week

* Sarracenias are carnivorous pitcher plants that can be grown in boggy areas outside in summer. In winter take them down and bring into a sheltered greenhouse. Cut down the watering to almost nothing during this naturally dormant phase.

* Remove the water-collecting dishes and saucers under outdoor containers to help them drain better through winter months. Stand pots on stones or special feet to aid drainage and in frost-prone areas wrap special types in bubble wrap.

* With chrysanthemums used for picking, cut them down and lift crowns with a spade.

Pot them up and bring into a sheltered windowsill or greenhouse, keeping them cool and almost dry through winter.

* Roses and other bare-root shrubs can be ordered inexpensively compared to pot-grown specimens and planted now. When they arrive make sure the roots are damp at all times but do not leave them plunged in buckets of water.