Spacing - Not an Exact Science

Ever had the experience of having to fill in space between plants? Maybe something died, or you hated it and hauled it out. (If it died, maybe it hated you. I should really write a post on plant suicide sometime.) Or perhaps you're starting from scratch and grappling with those wonderful books where they tell you how big and how wide your plants will get. They usually go on to tell you to map out your new garden on graph paper, using the measurements to figure out how many of each you need.

I don't want to knock the graph-paper method, but the problem is that once you've got the plants in the ground, they tend to have their own ideas about how big (or not) they want to be. There's only so much you can do about that.


There's also the nature of the plant itself to contend with. Some geraniums will spread and spread, which can be bad for any plants nearby. For example, I once had to fill in a space next to a fully-established geranium 'Patricia', and I decided on a group of lobelia 'Tania'. These are very upright, narrow plants, with dark leaves and shocking pink flowers. I put out my babies, and soon the geranium was snaking around them. Fine, once they get big enough not to be smothered, but until then I had to keep cutting back. Nature does indeed abhor a vacuum, it seems.

It's probably best to plan around the behemoths right from the beginning, because when you first buy your plants, especially if it's by mail order, they're often in those 9 cm pots, and they all look tiny and innocent. It's only after they've put on some growth that you realise that your miscanthus, for example, is beginning to resemble a bamboo grove, and the rubdeckias are taking over the border. Oriental poppies are another one to look out for.

Some plants are just complete takeover merchants - centaurea montana or mountain cornflower is a good example, perhaps because I should never have put it in lush border soil in the first place.

Centaurea montana, photo by Simon  Ross

The worst of it is, it regenerates from any tiny piece of root left in the ground, so I spent two years digging out its clones. (Free to Hollywood - never mind zombies, how about a monster that can reproduce from a sliver of claw, or skin?) In British gardening magazines plants like these are usually referred to as "thugs", which seems a little extreme. Frustrations boiling over, I guess.

On the other end of the scale are the frail darlings that you may love, but can't stand up to any bullying from the others. My iris chrysographes was one of those.

Iris chrysographes, Creative Commons, by jacki-dee

It's a really beautiful plant - it has flowers of darkest purple, almost like black velvet, with gold tracing all over them. They're very short irises, maybe eight inches tall, and I had planted them at the front of the border. The leaves of everything I'd planted to take over the show later kept trying to smother them. For most plants, I would have said to hell with it, smother. Not for these.

Everyone's got their own favourites, who get pampered while the rest have to fend for themselves. Maybe that's why they get so big and brawny; they know in advance that there's no special treatment for them.

In the same way, once you've had the experience of half your plants running amok and smothering the other half once or twice, you're on your way to understanding the science of spacing.