Garden Word of the Day
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We’ve all heard of collard greens, but what if you could grow these healthful leafy greens year-round? It ends up you can.
There are several types of tree collards. The two most common are tree cabbage or tree kale (Brassica oleracea var. acephala) and Jersey cabbage (Brassica oleracea longata). These cousins of broccoli, Brussels sprouts, cabbage, cauliflower, kale, and kohlrabi are not annuals that must be replanted each spring. Instead, they are perennials. And they lack the oxalic acid that makes other members of this group taste bitter.
Tree collards description
Instead of shrub-like mounds of kale or collard greens, these tall stalks look something akin to a palm tree. They can grow 8–10’ tall, but most people trim them to half that height to keep them bushy and less likely to fall over. Tree collards grow as a single stalk with a crown of large, purplish-green, edible leaves. The more purple you see, the sweeter they taste. Stems often have a white, powdery coating that is said to reflect damaging summer sunlight.
These shrubs can live for 20 years but are most productive when replaced after 4 or 5 years. Tree collards can withstand winter temperatures as low as 20°F (-7°C), but they grow best in USDA Hardiness Zones 8–11.
How to grow tree collards
Tree collards are best grown from certified pest- and disease-free rootstock, planted in either spring or autumn. These plants are sturdy and do not require special treatment once established. If you know someone who already has tree collards, ask for some cuttings. Cuttings should be 4–6” long and about twice the diameter of a pencil. This method requires daily light watering and can take 4–8 weeks, so don’t give up. Tree collards can also be grown from seeds.
While tree collards prefer growing in the ground, you can also use a large container that is at least 15 gallons in size.
Where to grow tree collards
Tree collards should be three feet apart. And they will readily cross-pollinate with other members of the cabbage family. Tree collards grow best in nutrient-rich, slightly alkaline soil.
Tree collards thrive in dappled shade and prefer protection from afternoon sunlight. They do not grow well in full shade.
Tree collards are relatively drought tolerant but perform best in well-aerated soil with regular mulching and top dressing. And they’ll grow bigger and better with regular irrigation in summer. It’s always a good idea to have your soil tested by a reputable lab before fertilizing. Adding too many nutrients can cause more problems than nutrient deficiencies.
Tree collards pests and diseases
These plants are relatively trouble-free. Imported cabbageworm butterflies are the primary pest of tree collards. Handpicking the caterpillars and extermigating the eggs are your best control methods. Snails and slugs are less of a problem than seen on their shorter cousins. And aphid infestations tend to be localized and short-lived. Let the ladybugs and other beneficial insects take care of those pests for you. Ladybugs won’t be able to do anything about the deer and other herbivores, though.
Powdery mildew is a common problem for tree collards, so maintain good airflow and keep your plants healthy.
To keep your tree collards attractive and productive, it’s a good idea to prune out stems as you harvest leaves. If you want your tree collards to reach full height, you may want to stake them upright. When growing naturally, they tend to fall over, creating an arching tangle similar to a blackberry bramble.
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