A few of the rocks we’ve collected …

I’ve been struggling with what to do with my tender seedlings here at the new house. I hesitate to keep them in the house, knowing the amount of moisture they produce. It wouldn’t do to turn the new house into a humid greenhouse.

What I really need is a heated greenhouse, but that’s a luxury I don’t expect to ever have.

At the old house, I lined the perimeter of the greenhouse with water bottles to trap solar energy during the day and release it at night. I recycled all those bottles before the move, so I have nothing to keep the greenhouse warm at night now.

Except the other day I picked up a paperweight from my desk—a rock I’d collected from the beach. It had been in the sun and was positively hot to touch.

Of course! Store solar energy in rocks. It’s a technique that was used by Māori for hundreds of years in Canterbury to grow semi-tropical crops in this cool climate.

Perhaps I hadn’t thought of it before, because the previous vegetable garden was nearly rock free. But we’ve already picked tonnes (literally) of rock from the soil here. I can practically pave the greenhouse with sunlight-absorbing rock that will warm the plants all night.

It will take some thought—I really don’t want to add rocks to areas I’ll be tilling and planting each year, but I like the idea of using the materials available on site to solve a problem.

Now we have to figure out how to use all the rest of the rocks …