What is the ‘three sisters’ growing method and does it work?

Lack of outdoor space is an ever-increasing problem for urban gardeners, who often try to cram too much into their plot, with varying results.

Anyone who wants to grow a variety of produce with just a small raised bed or tiny border may be scratching their heads wondering how they’re going to do it.

But there is an ancient companion planting technique, called ‘three sisters’, which may go some way to help.

It started out as a system used by indigenous North American tribes for growing sweetcorn, beans and squash together, maintaining that these ‘three sisters’ grew best as part of a symbiotic relationship.

The corn supported the climbing (runner) beans, which enriched the soil with nitrogen, while the squash grew underneath, creating good ground cover and helping to suppress weeds and retain moisture.

“We’ve moved away from that idea of just a single crop in a bed with bare soil inbetween the plant,” says Paul Kettell, garden manager in charge of edibles at RHS Garden Wisley in Surrey.

How would this work in the modern garden?

Kettell has reservations about planting the original ‘three sisters’ veg – climbing beans, sweetcorn and squash – in the UK.

“In principle it looks like a really clever system where you get three crops instead of one in the same piece of land. I’ve tried it myself in gardens before but in my opinion it rarely works because it’s a slight misinterpretation of what the Native Americans were doing.

“They were growing in a part of the world with higher light levels than we have and hotter summers. As I understand it, they were growing beans for drying, corn for milling and squash, crops which are quite vigorous.

“You’d leave those until the end of the summer, when your squashes are ripe and your beans are dried, and harvest them all at the same time.

“When people translate it to the UK and grow sweetcorn, runner beans and squash, I found the runner beans normally swamp the sweetcorn and can often be so vigorous that they pull the sweetcorn over.

“If you are going to attempt it in the UK, you need to have your sweetcorn already a good foot or two tall before you plant a runner bean at the base of it.

“If you look at the space your squashes take up, it can be problematic getting in to regularly harvest your runner beans throughout the summer. You’ll be treading on the squashes, stems, leaves and the fruits themselves. It becomes really difficult to access the beans.”

Crops which might work

“We might have tomatoes growing up a frame and underneath it might be full of marigolds and basil, a classic combination, instead of that bare soil around the base of the tomato,” Kettell explains.

“I think you could be quite successful growing sweetcorn and then having a trailing squash growing at the base. If I was doing it in my allotment, I would happily do that. But I would probably grow my beans on the edge of that plot on wigwams with canes.”

At the RHS flagship garden at Wisley, gardeners grow combinations of plants all the time, allowing some to grow around the base of others, he stresses.

If your soil isn’t stony, you could even have root vegetables such as carrots growing at the base of your wigwam right next to your climbers, as long as they are not situated in the middle of the wigwam because they need plenty of light, he suggests.

Train fruit trees

“Try different things. Along our boundary we have all our trained fruit here in the World Food Garden at Wisley,” he explains.

“We’ve now got Alpine strawberries which we’ve allowed to spread through there. We’ve got marjoram and oregano growing along the base, which is covering bare soil and protecting that soil health, in combination with the apple trees that are trained around it.”

But you’re not limited to apple trees.

“We have pears and plums. We even have Sichuan peppers that we are wall training that have plants growing around their base.

“We also have figs and all the hybrid soft berries you can think of, gooseberries and redcurrants and they’ve all got thyme and oregano and Alpine strawberries growing around their base and they are doing brilliantly.”