Tree Collard Basics

What are tree collards?

Tree collards are members of the brassica family (Brassica oleracea var. acephala) Their relatives include traditional collards, kale, broccoli, cabbage, brussels sprouts, kohlrabi, and cauliflower. However, unlike most of its relatives, tree collards are perennial. This means that, like a fruit tree or rose bush, once you plant them they will continue to grow and produce year after year. Traditional collards, kale, etc. must be grown from seed each year and then die after they go to seed. This is one of the top reasons why so many people love tree collards- once you have a plant established you don’t have to plant new seeds or seedlings every year.  They are closely related to perennial collards traditionally grown in Portugal and many countries in Africa, although they are different.  Tree collards are thought by some to have been brought to the US by enslaved Africans though research has not progressed very far on this topic.  Others say that tree collards were introduced to California from the island of Jersey in the English Channel (where they were grown as animal fodder) in the mid 18th century.  Yet another theory is that purple tree collards came to California from the Southern USA during WWII.  

How to Start Tree Collards 

There are 3 ways to start a tree collard:  already rooted plants, cuttings, or seeds.

The easiest and quickest method is to purchase plants that have already been rooted.  They will likely adjust to their new home soil relatively quickly and are not demanding or fussy plants.  Depending on the climate and time of year, they generally grow quickly.  If you live in a place with hot summer temperatures, you will probably want to start growing your plants in spring or fall to get them established.  Planting during temperatures around 100 degrees F makes it harder for the plants to acclimate.  I

It is relatively easy to start tree collards from cuttings.  They are usually sold in bundles of 3 or 4 cuttings because not EVERY cutting makes it.  We have a complete tutorial on how to propagate tree collards from cuttings here. Starting tree collards from cuttings usually requires daily watering and/or daily moisture checks, which is a similar commitment one needs to grow plants successfully from seed.  One needs to be able to not overwater them while still keeping them moist while rooting.  Depending on the time of year and climate, it can take anywhere from 3 to 8 weeks.  

The last method of growing tree collards is from seed.  Some varieties of tree collards bloom.  It does NOT mean that they are annual or that they are dying.  If you want to propagate tree collards from seed, be aware that tree collards easily cross-pollinate with other members of the brassica family, so they may or may not have the same or similar traits to the parent plant.  We sell 3 different types of seed and have had a lot of positive feedback about successful germination.

Lastly, take some time considering where to plant your tree collards in your garden. If planted in fertile soil they can grow over eight feet tall depending on the variety! For this reason, some tree collards are a great way to create a privacy screen in your garden. Tree collards also provide year round interest with their beautiful leaves.

Climate

Tree collards prefer full sun in more temperate climates like much of the west coast, and afternoon or dappled shade in hot climates.  They are most easily grown in USDA zones 8-10 (7 is marginal) thus, tree collards are especially suited to mild climates, such as those on the pacific and southern coasts of the United States. Tree collards are hardy down to 20° Fahrenheit (possibly even the high teens) for short time periods, and have been successfully grown in Las Vegas with temperatures of 115°.  If your area usually gets below 25°, we recommend keeping one of your plants in a small pot that can be brought into a protected area during cold spells. Your plants may survive down into the teens, but we recommend protecting at least one of your plants as a backup. You can then propagate new plants from this one if the others don’t survive. Another option is to take cuttings right before the cold weather sets in, wrap them in a plastic bag, and store them in the refrigerator. We’ve kept them for over two months in the fridge like this, then successfully propagated new plants. If you have two months of really cold weather, you could keep cuttings in the fridge, then root them in a protected greenhouse for a month and be ready to plant them outdoors when the weather improves. Others report growing them through new England winters in greenhouses kept at 30°. Our customers have grown them in Norway, Maine, and Montana using experimental techniques in overwintering. If they are exposed to temperatures below 20° for an extended period of time, your plants will die and you will have to start new ones.  

Planting tree collards

Tree collards, like most vegetables, prefer a soil with with a fair amount of organic matter and a pH around 6.5. However, they can tolerate a range of soil types and growing conditions. In a hot climate it would be best to plant your collards in under the canopy of a deciduous tree that casts dappled shade or in an area with afternoon shade. They do not thrive in full shade in any climate.  In our mild climate they are planted in full sun and love it.

The actual process of planting your collards is very simple. You’ll likely want to incorporate some well-aged compost or manure to your planting area and loosen the soil with a garden fork or spade. (You can also use no till methods)  Space your tree collards two and a half to three feet on center.  Choose your spot with eventual height in mind so you don’t cast shade onto other sun-loving plants. Remember that tree collards can reach over eight feet in height in fertile soil with regular water and proper staking. They can also be kept to four feet. You can use some varieties of tree collards to screen out an unsightly view of the neighbors or create a privacy screen.

If you don’t have a garden bed or want to keep your tree collards portable, you can plant your tree collards in a large pot.

Watering, Staking, and Fertilizing

Tree collards thrive with low to moderate water and well-aerated soil rich in organic matter. In drought conditions, tree collards respond by producing smaller leaves and growing slower.  They also have a white powdery coating on the stems which is one of its clever drought adaptations to reflect light. They can live a surprisingly long time with minimal water. 

However, if you want large plants with a big harvest, you will need to make sure they get supplemental irrigation during dry periods. 

Tree collards don’t necessarily need to be staked but if you want them to grow like a tree, you will need to provide a strong stake such as a metal t-post or rebar to hold them up once they reach 2-3’ high.  For this you will want the stake to be at least 6 feet above the ground.  If left un-staked, the ‘trunk’ will spread along the ground and send up numerous curving shoots that grow 2-3’ tall. Both methods work fine but if you have limited space, you will probably want to stake your collards in order to maximize space while maintaining high yields.  High winds or storms will break branches. This is normal but can be mitigated by staking and pruning your plants regularly.

If your young tree collards don’t thrive or produce large leaves, they are probably deficient in nitrogen. You can experiment by supplementing with a small feeding of fish emulsion or another natural nitrogen source. We do not advocate use of chemical fertilizers because they cause surges in growth that tend to attract insects and pests to attach. 

Tree collards also tend to need calcium supplementation and oyster flour from ground oyster shells are a good inexpensive source of calcium. We also give our plants some mineral rock dust a couple times a year to replace micro nutrients that are removed during harvests.  Tree collards appreciate yearly surface applications of compost and mulch.  This also cuts down on watering.

Pruning and Harvest

Tree collards require very little maintenance once established. If they are completely left unpruned, they will tend to develop long, leggy, woody stalks by their 2nd year that are unattractive and less productive. To create bushier, more compact growth, it is important to prune them when you harvest leaves or at least quarterly. We have a tutorial on pruning and harvesting here.

Pests

In Northern California where we grow our tree collards, they are relatively pest and disease free. When our broccoli and kale are getting hit by aphids, the tree collards are often unscathed. Our tree collards are also less affected by slugs and snails than smaller plants closer to the ground.  Our main pest is the white cabbage moth, who lay eggs on the leaves and catch into very hungry green caterpillars. The best option is to find the green caterpillars and remove them. BT spray may kill them, but even though it is approved for the organic gardening industry, it kills beneficial insects such as butterflies as well.  Each year during the summer tree collards do get a bit of powdery mildew on older leaves,  so we pick these off and compost them or feed them to our poultry. Deer (and all ruminants) love tree collards, so it is important to plant them  in protected areas!

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