The landscape where everyone’s a winner

Last spring I installed a garden on top of a septic leach bed.

As you can see, the glamour of my life never ends. Hours were spent placing 1,200 small plants in little black plastic pots 12 inches apart. The site looked like a square of dots on clean light brown soil, alien amid the clearing in the trees.

After the plants were in the ground came the clearing up – 1,200 empty pots had to be put in the trunk of the car.

The clients wanted something other than grass on their septic – a bit of colour by the driveway and more nature at their cottage.

It was a part-shaded site on sandy soil, so I chose plants that matched the conditions.

The matrix layer – the layer of plants that ties together the design and acts as a groundcover – was made up of a species of sedge.

In clumps and drifts throughout the garden were flowering perennials that liked dry conditions and which didn’t have deep roots that would disrupt the functioning of the septic. The plants were chosen so that together they would provide blooms throughout the growing season.

I put the more aggressive spreaders next to each other so they would keep each other in check. Less aggressive plants were left solo because they wouldn’t bother their neighbours.

Fungal business

Toby Kiers is an evolutionary biologist at Vrije University in Amsterdam who studies mycorrhizal fungi – the underground networks that connect plant roots. She won a “green Nobel” for her research that showed these networks aren’t just passive plumbing.

The fungi, she found, are strategic traders. They send nutrients to plants that give them the most carbon in return. They withhold nutrients from plants that don’t give much back. And they adjust what they do depending on competition from other fungi. They’re selfish. But it works.

Kiers studied what happens with fungi. But the same thing happens when I design a landscape. Plants don’t negotiate for themselves, they just follow their nature. So when I put them together, I create the cooperation fungi create.

When I chose plants for this septic bed, I found the kind of sedge and perennials that thrive in part-sun, sandy conditions of the septic bed and paired them by habit – aggressive with aggressive, gentle with gentle.

The narrow-leaf mountain mint is a picture of abundance. It provides food to scores of different insects, attracting pollinators for the other plants in the landscape. It grows vigorously but is kept in check by the spreading of the pearly everlasting. Together, each plant stops the other dominating.

The black-eyed Susans don’t live long, but they seed like crazy, their offspring popping up on patches of bare soil, helping quickly cover the ground. These live-fast, die-young plants have a propagation strategy that works for them, but it also helps the overall ecosystem.

Growing together

I visited the site again later in the year. The sedges on the slope had started to fill in – each plant about twice its original size and much less bare soil.

The black-eyed Susans had finished flowering and were developing seed heads, ready to make new plants next year.

The pearly everlasting was in bloom – its flowers begin in August and stick around until the frost turns them crispy.

The mountain mint had added twice as many shoots, creating a feathery canopy over the matrix of sedges.

The site had started to look like a community instead of a collection of 1,200 individual plants, fresh out of their black plastic pots.