Tree collards (Brassica oleracea var. acephala) are members of the brassica family. They are also known as Tree Kale or Tree Cabbage. 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, they will continue to grow and produce year after year and without the need for planting new seeds or seedlings every year like traditional collards and kale. Tree collards are hardy to about 20° F (-7° c) and in mild climates have been known to live for up to twenty years! They are closely related to other perennial collard varieties grown in Mediterranean, Africa, the Americas, and other countries.
Learn Tree Collard Basics
Rooted Plants
The easiest and quickest method to get tree collards producing in your garden is to purchase plants that have already been rooted. If you prepare your beds with compost and plant them in a location with good drainage, they will likely adjust to their new soil relatively quickly as they are not demanding or fussy plants. Depending on the climate and time of year, they generally grow as soon as they are acclimated. 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 above 90 degrees °F makes it harder for the plants to acclimate. Likewise, if it is below 40 degrees °F, it will be a challenge for them to get established. This is what we recommend for beginner gardeners or those who need their plants to become productive ASAP.
Cuttings
While it is relatively easy to start tree collards from cuttings it takes a few minutes of DAILY attention until the plants have rooted. They are usually sold in bundles of 3 or 4 cuttings because often not all cuttings will make it. Some customers are unable to successfully root any of them. For this reason, we do NOT recommend that beginner gardeners buy cuttings because it may be easier to start with a rooted plant. Once the plant is a 3-4 months old, the beginner gardener can try their hand at rooting their own cuttings from their own plant. This mitigates the financial risk. We have a complete tutorial on how to propagate tree collards from cuttings below. 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. It is important to not overwater them, while still keeping them moist enough to root. Depending on the time of year and climate, it can take anywhere from 4 to 8 weeks. In temperate climates that rarely freeze or get hot, cuttings will root easily all year. However, cuttings do not root well in the coldest nor the warmest months in areas with 4 seasons. In these areas, it is best to order cuttings in spring or fall when temperatures are in the 50s to 70s.
If you order tree collard cuttings in the mail, we recommend our simple directions included to help make sure that your collards get off to a great start. It requires only potting soil, containers, and cuttings and is the same way we propagate our plants for sale. You may find other information/techniques for rooting including: water cloning machines, using rooting hormones, and rooting in water. While these may work sometimes, we have not found these methods to work as consistently. Even one happy plant can get you started and you can take more cuttings of it once it has taken off.
The basic steps for rooting a tree collard are: take a cutting, plant it in a container with potting soil, keep the soil moist in appropriate lighting, and wait patiently for your new plant to grow. Below is an updated video we made in 2020 on propagating tree collards from cuttings, followed by a more detailed written explanation.
Take a Cutting
You want to take your cuttings from fresh growth on the tips of an existing tree collard, making sure they are four to six inches long. The cut on the bottom should be cut at an angle. Next, cut off all of the leaves, except for 2-3 tiny ones on the very top of the cutting. Leaves respire a fair amount of water so you need to remove them. It is fine if a cutting isn’t particularly straight as tree collards eventually get curly growth. The diameter of the cutting should be at least as wide as a pencil. Wider cuttings usually take off more quickly, but not always.
Plant cutting in a container with potting soil
We suggest using a second hand 4 inch or one gallon sized nursery container. If you don’t have one, an alternative is to create 4-5 quarter inch holes in the bottom of a quart yogurt container or something similar. Holes on the bottom are critical for proper drainage or the cutting may rot.
Fill the container with a high quality potting soil. We have used “Recipe 420” potting soil by EB Stone and Happy Frog Potting Soil by Foxfarm, but any organic and natural potting soil available in your area will be a good choice. A good potting soil will hold on to a lot of water but will still drain well. If you don’t have access to potting soil, you can also use perlite, vermiculite, and all purpose sand mixed with some compost. Garden soil on the other hand can be very ‘heavy’ and not drain very well in a nursery can but if you don’t have any other options, try using garden soil that is very high in organic matter (for example, collect soil from under a pile of rotting branches and leaves).
Tap your container with the potting soil down on a hard surface to help it settle. Then stick the cutting two thirds or even further in your soil. Gently press your fingers or fist down around the cutting. Now it is time to water it.
Keep the cuttings moist but not waterlogged. Depending on the temperature and sun exposure, you will likely need to water the cuttings daily.
During a warm time of year you’ll want to keep your cuttings in containers somewhere semi-shady that is protected from full sun. They do need some sun daily, so dappled or filtered sun is good. Morning sun is less intense than afternoon sun. During cooler months, shade isn’t critical, in fact your plant will root faster in the sun as long as it doesn’t get too hot and dry out. Tree collards can tolerate some freezing weather once established, but it is best to protect your cuttings from hard freezes until they have roots and are planted in the ground. In warm times of year you’ll want to water the cuttings at least once a day. Again, it is best to root cuttings in temperatures of 50s to 70s.
Have patience
Besides keeping the soil around the cuttings moist, you should leave them alone. Don’t pull them out to check for roots. They might be there and you might accidentally break them off when you’re trying to check on them. Wait for the tree collards to start growing new leaves. Once your tree collard plant have a fair amount of new growth and you can perhaps see a couple roots poking out your pot’s drainage holes, you’ll know it’s time to plant it in the garden. Four to six weeks is a fairly common wait time, though it can take longer.
Seeds
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 they 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 8 different types of seed and have had a lot of positive feedback about successful germination.
Where to plant your Tree Collards
Like most vegetables, tree collards 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 three or four feet, without staking.
Take some time considering where to plant 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 can also provide year round interest with their beautiful leaves.
If you don’t have a garden bed or want to keep your tree collards portable, you can plant tree collards in a large pot (15 gallon minimum) on a deck or patio. Wooden planters, clay or plastic pots, grow bags, and 1/2 wine barrels are all possible containers you can use.
Climate
Tree collards prefer full sun in more temperate climates like much of the west coast, and afternoon or dappled shade in hotter climates. They are most easily grown in USDA zones 8-11 (7 A and 7B are 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 up to 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, Montana, and beyond using experimental techniques in overwintering. If they are exposed to temperatures below 20° for an extended period of time, tree collards will die and you will have to start new ones.
Watering
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 help 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.
Keep in mind that tree collards do not like soggy or wet conditions so if you live in an area prone to extended heavy rains or flooding, you need to find a well-drained location for your tree collards or they will die.
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. Sometimes the aphids will attack one particular area, and leave the rest alone. This is normal and if we leave the aphids alone, usually the ladybugs or other beneficial insects step in to help restore the balance.
Our tree collards are also less affected by slugs and snails than smaller plants closer to the ground such as kale. Slugs usually nibble the leaves closest to the ground in the winter. Our main pest however, is the white cabbage moth, who lay eggs on the leaves and hatch into tiny very hungry green caterpillars. They grow to 1 inch long after they eat a lot of leaves. 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!
Fertilizing
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 application 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 attack.
Tree collards also appreciate calcium supplementation quarterly. Ground oyster flour from ground oyster shells is a good inexpensive source of calcium and ground eggshells from chickens, ducks, etc. are wonderful as well. 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 and helps them stay warmer in cold winters, and cooler in the summer heat.
Pruning, Staking, & Harvesting
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. In the video below, you will see how we prune the tips to keep them bushier and more dense.
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. However, if you want large plants with a big harvest, you will need to make sure they get supplemental irrigation during dry periods.