Plant a Tree Collard

Plant a Tree Collard
Now is the time!

By Joshua Burman Thayer

As winter brings shorter days and cooler temperatures, our gardens enjoy a reprieve from the dryness of summer. More moisture comes not only from winter rains, but also from condensation as the dew point rises. The dew point is the atmospheric temperature (varying according to pressure and humidity) below which water droplets begin to condense, causing dew to form.

But there’s a downside for gardeners. Cooler soil temperature and the higher dew point can lead to powdery mildew and botrytis mold creeping in among our late season grapes, tomatoes, and other lingering fruits and vegetables. That’s why this is a good time to focus on a different set of plants, the ones we refer to as cool-season crops.  

Among my favorite cool-season additions to the garden is the tree collard. This unique member of the cabbage family (Brassicaceae) is able to continue growing season after season as a perennial, climbing upward each year toward the sky. If you have ever wondered about adding a perennial crop inside or near your raised beds full of annuals, tree collards are a good choice. Here are some fun ways to incorporate them into your cool-season beds:

Plant the Northern Boundary

Tree collards can grow to seven feet tall, which in a small urban raised bed could mean shading out other plants looking for sunlight. This is why you should place these tall plants on the northern boundary of your production zone. 

Use Tree Collards as a Trellis

Once your tree collards reach about two feet tall, you can turn them into trellises for cool-season climbing peas. I like sugar snap peas for this purpose. The peas will sprout and wind their way up the stalk without hurting the tree collards. Brassicas in general tolerate bio-intensive production and won’t get sick just because other leaves are touching their surfaces. Come spring, the tree collards will still be there, and then you can re-plant at their base with a warm-season climbing bean such as scarlet runner.

Scissor-Cut a Weekly Harvest

I recommend harvesting leaves from your tree collards when they are palm size or smaller. Once they get donkey-ear size they are quite bitter. By going into your garden for weekly or bi-monthly cuttings, you can have a steady harvest of tasty and healthy greens and also reduce the likelihood of losing the older leaves to powdery mildew. 

Peppermint Foliar Spray for Healthy Plants

As the cool season can be a time of mold and mildew, I recommend spraying your susceptible plants with peppermint oil once a week as the dew point rises at sundown. Simply fill a 750 ml spray bottle with water and add 10 drops of peppermint oil. Spraying the leaves with this mixture will prevent the onset of mildew and mold. To remove the peppermint flavor, soak leaves in a large bowl of clean water for 30 minutes.

Photo: Joshua Burman Thayer

Permaculture designer and educator Joshua Burman Thayer is a regular contributor to Edible East Bay. In his monthly Gardener’s Notebook feature in Edible East Bay’s free e-newsletter, he offers lots more advice on how to implement gardening ideas like this one. Sign up for the newsletter here. Josh has also written for Mother Earth News and Edible Silicon Valley. Find him and his work at, and follow him on Twitter at @nativesungarden.