Boysenberry Plants: Bountiful Big Purple Berries

16 min read

Boysenberry plants (Rubis ursinus x Rubus idaeus) grow a large reddish to dark purple berry that springs after small white flowers are spent. They are sometimes thorny, sometimes not, and are grown in several USDA zones. Boysenberries have a rich past, and a flavor that is loved across the United States due to their popularization via Knott’s Berry Farm.

A Rubus ursinus x Rubus idaeus plant needs some maintenance throughout its life. If they are pruned correctly and allowed to lie dormant in winter, they produce fresh purple berries the following summer in your garden. In July when boysenberries are close to the end of their fruiting phase, they have the sweet yet tangy taste that so many people love.

If you’ve tried growing blackberry, then you already understand the process for growing this dark hybrid berry. Maybe this is a sign you need to set up a trellis and try growing boysenberries? Berries of this kind aren’t too finicky and help novice gardeners learn more about the dedication berry production requires.

This spring, stop at your local nursery to see if they have a boysenberry plant you can grow yourself. Especially if your location is in one of the growing zones listed below, you’ll probably have success with boysenberries. And who doesn’t want sweet summer fruit?

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Quick Care Guide

Common Name(s)	Boysenberry
Scientific Name	Rubus ursinus x Rubus idaeus
Days to Harvest	1 year
Light	Full sun
Water	1 to 2 inches per week
Soil	Rich, well-draining
Fertilizer	Full-spectrum slow-release fertilizer
Pests	Aphids, mites, leaf rollers, assorted raspberry pests, leafhoppers, birds
Diseases	Rusts, blights, anthracnose

The History Of Boysenberry Plants

The boysenberry is named after Walter Knott’s acquaintance, Rudolph “Rudy” Boysen who managed to create a hybrid of four berry plants: raspberries, blackberries, dewberries, and loganberries. They are the result of a long period of experimentation for Rudy. He developed his hybrid berry species in the 1920s.

Knott searched for boysenberries when word about the hybrid berries traveled to him and his friend at the USDA, George McMillan Darrow. They looked and found Boysen, but he had sold his Coombsville, California farm. What berry plants remained there had gone wild, but with Boysen’s permission, they managed to take some canes back to Knott’s berry farm and restore them. Knott began selling berries in 1932 after developing a thornless variety from the original canes. Rudy Boysen’s family managed to keep another original thorned cane, which ended up on their property in Merced.

Original plants saved from Boysen’s farm were rediscovered when Rudy’s granddaughter was contacted by a historian who wanted to know more about the plant. In 2018, the Boysen family reopened their berry farm, located now in Orland, California. The new farm has 2400 vines that descend directly from the original thorned canes that have survived 100 years.

Today, Knott’s Berry Farm sells boysenberry everything, but the thornless plants that Knott had developed are hard to find at a nursery. The farm has become a 57-acre theme park that includes roller coasters, a waterpark, and a marketplace. In the early part of the year, they occasionally have boysenberry plants for sale, and their stores and restaurants carry boysenberry products year-round.

What resulted from all of this experimentation is a star, especially in California where hundreds of acres have been devoted to growing this thin-skinned, sweet berry.

All About Boysenberry Plants

Fruiting on floricanes — Fruit is produced on second-year floricanes. Source: Pussreboots

Botanically, boysenberry is known as Rubis ursinus x Rubus idaeus. Because they are members of the rose family, they sometimes have thorns — unless they are the hybrid cultivar bred for its lack of thorns. They grow in bramble formation like blackberries. Young plants have branches, called primocanes, which start green and do not produce berries in the first year. They develop into floricanes, which produce after the bramble bush has overwintered and developed bark. The leaves of a boysenberry plant are much like raspberry or blackberry leaves: obtuse with serrated edges arranged in threes.

The flowers of a boysenberry plant are small, white, and have five petals. They bloom and die in the second year and dark purple fruit sets. Boysenberries are made of a group of drupelets that form from multiple carpels present in the flower.

Rubus ursinus x Rubus idaeus berries are about 1.5 inches long. Each weighs about 8 grams. Berries are rich in anthocyanins which provide the body with heart-healthy nutrients. It’s because of this they are considered a superfood. They have great flavor crossed between sweet and tart when they are fresh. A boysenberry plant will often put out suckers that can be removed to propagate more plants, or allowed to remain so the vine can spread.

Planting Boysenberries

Transplant boysenberry starts in spring after the last frost, or at least 8 weeks before the first fall frost. You’ll need space for these brambles, as they spread, and they’ll need a trellis for support and training. Give them at least two feet of spacing between them and the next plant for spreading room.

Transplant boysenberries in a prepared garden bed or an 18 inch wide, 14-inch deep container in full sun. Both in-ground and container-bound boysenberry plants need good drainage. Plant cane snips with two sets of leaves, one above the soil line and one below the soil surface. In about one month, new leaves will grow to indicate the cane has rooted. Canes need good moisture retention, which is why wood chip mulch is recommended.

Care

Boysenberry leaves — Boysenberry leaf edges are distinctly jagged or sawtoothed. Source: Pussreboots

A boysenberry plant, like blackberry, tends to produce in the subsequent year after planting. Give them what they need, and they’ll last for up to 20 years.

Sun and Temperature

Boysenberries need full sun, with at least six to eight hours of direct sunlight daily. They are perennial in zones 5 through 9. These plants need warmer temperatures to fruit, but over 85 degrees daily requires full afternoon shade. Dormant, properly pruned plants can survive freezing winters, but foliage cannot. Canes need at least 100 cold hours, and up to 300 total.

Protect foliage in a snap freeze with a frost cloth. Try not to plant in low-lying areas where cold air and frost accumulate, or in areas where sun and temperatures above 85 degrees will overexpose your boysenberry plant.

Water and Humidity

Water boysenberries in the morning or at dusk every few days in drier seasons. Their soil should remain moist, but not drenched, and the total count of water per week should be about 1 to 2 inches.

Because most berry plants are prone to rusts and rots, water from below. Drip irrigation or a soaker hose makes it easy to water deep and low and avoid getting foliage wet. If the season is particularly wet, you may not need to water. Dip your finger a couple of inches below the surface of the soil. If it’s dry, add some water. Avoid dryness as boysenberries aren’t acclimated to drought. Even moisture applied when watering promotes good production.

Soil

A boysenberry plant prefers loamy, well-draining soil rich with organic matter. The soil pH should be slightly acidic at 5.8 to 6.5. Neutral soils at 6 to 7 pH work as well. They do not grow well in compacted, poor soil. Provide amendments of well-rotted compost to the container or garden bed where you’ll grow your boysenberry plant. Mulch around the base of plants to prevent weed growth close to the cane mass.

Fertilizing

Boysenberry flowers don’t look like much, but form great fruit later. Source: Pussreboots

One rule of thumb for fertilizing boysenberries is to avoid fertilizing in the cold seasons when they are dormant. Otherwise, add a 20-20-20 NPK fertilizer in the form of slow-release granules or powder as new growth appears, and then every four weeks after that until harvest. Blood meal and fish meal are good for boysenberries. Containers need fertilizer more often because nutrients tend to wash out as they drain through the soil.

Pruning

Pruning thorny vines can be tricky, so wear sturdy gloves. Make sure to only prune floricanes to the ground in autumn, and avoid pruning primocanes that set fruit the following year. Distinguish them by their color. Floricanes have a bark-covered surface, while primocanes are green. Cut floricanes down to the ground, leave the primocanes, and then thin primocanes on each bush to about seven.

Vines benefit from maintenance during their growing period too. Of course, it’s best to remove any damaged canes as you go. Cut the tips of new growth primocanes to help them produce more. This gives you more room for flower production, which means more fruit. Prune off suckers as they arise if you are controlling the spread of your boysenberry plant.

Propagation

Boysenberries propagate easily from cuttings. Use the same transplanting process described in the Planting section of this article to guide you. Canes can be planted in containers, or they can be planted in beds where they develop roots. Remember to give them lots of room. This is the primary mode of propagation a nursery would use to help boysenberries root.

Each boysenberry plant attempts to self-propagate through small suckers that develop from winding roots that spread out beyond the perimeter of the plant. Detach them, and plant them in the soil where they’ll develop new roots, and spread the love boysenberries provide.

They also grow from sprawling rhizomes left in the ground. Divide these roots into multiple plants in spring. Each division needs at least one primocane to produce a viable root. After you divide them, plant them in their designated zone.

Harvesting and Storing

In some zones, growers release boysenberries from the vine in May. Others pick berries in July and August. Whatever month you harvest, follow this guide to learn how to pick and store the fruit of your boysenberry plant.

Harvesting

Fresh boysenberries tend to be extremely delicate, resulting in them not being a common sight at markets. That delicate nature means you should be cautious during the harvest process so that you don’t damage your fruit.

In warmer climates, berries are picked as early as May when they are dark purple. In a colder zone, July and August are the best times for berries. If there is hot weather in the late spring, you’ll have to harvest earlier so the boysenberries don’t spoil on the vine.

To remove boysenberries, gently pick them off the plant without squeezing them, and put them in a basket or tray. Try not to pile too many boysenberries on top of one another because their skin is fragile and they bruise easily. Keep them cool until use.

To rinse them, gently place them in a colander and dip them in water. Then, pull the colander out and allow the boysenberries to dry completely. Use a paper towel.

Storing

Fresh boysenberries are best eaten right away. They won’t last for more than a few days at most before they start to spoil.

For longer-term storage, freeze them and keep them to include their flavor in winter pies and preserves. The berries keep in a plastic bag in the freezer for up to four months. If you dehydrate the fruit, boysenberries keep for up to 5 years. Jams will keep for one year. Perhaps the best way to store them for the long term is to freeze-dry them. If carried out properly, freeze-dried boysenberries keep for up to 15 years.

Troubleshooting Boysenberry Plants

Drought damaged berries — Drought can cause leaf edges to yellow and brown. Consistently water! Source: Br3nda

Although boysenberries are related to blackberries, they have different issues. Provide them with the right support and they’ll give you berries for many years. Here are a few of the issues you might encounter growing them.

Growing Problems

Boysenberries that sit in a hot area above 85 degrees for extended periods wilt and won’t yield. Shade cloth can help with this. However, some areas experiencing upswings in temperature will need extra support in the form of careful placement, proper sunlight, and attentive monitoring to catch problems before they become severe.

To protect your boysenberries from cold, prune them and mulch the area around the remaining primocanes. This traps heat in the soil near the roots and gives them the extra support needed to survive winter. Prune off any fresh tips before winter arrives, and you’ll prevent cold damage on foliage too. If parts of the primocane turn black, this is a sign the plant has suffered cold damage. Prune off damaged canes.

If your boysenberries are in a shadier-than-normal spot, it’s likely they aren’t getting enough light. One sign this is the case is when plants don’t develop drupes. Avoid planting brambles like blackberries and boysenberries close to trees or in the shade of buildings when possible.

If brambles don’t have the support of a trellis, they go wild and get easily tangled. Add thorns to this, and you’re in for it! So keep a trellis close by when you plant them.

Inconsistent watering is a major problem. Boysenberries need ample water supplies and will suffer when they don’t have enough moisture.

Pests

Birds love to eat berries. Blackberries and boysenberries are no exception. To keep birds from eating all of your berries, drape your plants in netting, which birds can’t penetrate. Old CDs or shiny tape tied around the branches of your berry plants may distract birds. Providing birds with water to quench their thirst is another way to distract them. If you’ve seen unripe berries in your garden one day, and they are gone the next, this is a sign birds are eating. Keep a watchful eye on them.

Aphids congregate and suck sap from the leaves of your boysenberry plants which can cause leaf curl. To rid your plant of them, apply insecticidal soap every seven to ten days. Neem oil is an effective treatment as well. If there are large outbreaks, consider using an organic pyrethrin spray.

Leaf rollers (Choristoneura rosaceana) start on your plants as larvae and develop into moths. If you see a small web that seems to adhere a folded leaf together, this is a sign of leaf rollers. They sometimes overwinter in plant debris. Application of beneficial nematodes to the soil will prevent spring emergence of overwintering larvae. Bacillus thuringiensis spray is an effective treatment to prevent larval spread on your plant.

Raspberry fruitworms, raspberry borers, and raspberry bud dagger moth larvae may all be attracted to the boysenberry plant. Fruitworms can be controlled using organic pyrethrin or spinosad sprays. The larvae of raspberry borers or the dagger moth are somewhat susceptible to Bacillus thuringiensis, but it’s less effective than good garden maintenance and hand removal of pests.

Leafhoppers are small pale yellow insects that feed on the undersides of boysenberry leaves. Neem oil, insecticidal soap, and pyrethrins are all effective organic control methods.

Diseases

Cane and leaf rusts are caused by fungi and can dry and crack all parts of the plant. Orange rust does similar damage but presents in small orange spots rather than larger brown spots. Prune off damaged material when discovered and apply either a sulfur-based fungicide or a copper-based fungicide to all remaining parts of the plant. Both sulfur and copper fungicides can be used as a preventative before rust appears, as well.

Anthracnose may develop on canes or leaves in the form of purple spots. Prune off damaged growth and apply a copper fungicide. Some biofungicides are also effective against anthracnose. It may take multiple treatments to eliminate the fungal source. To prevent anthracnose, do regular sprays of neem oil and ensure your plants have good airflow and are watered at the base. Avoid unnecessary foliar sprays.

Improper irrigation may cause root rot. One sign of root damage is yellowing leaves. If you notice this, carefully remove your canes from the soil and inspect the rhizomes for rotten points. Root rot can be prevented by ensuring your soil drains away excess water rather than pooling at root level.