How to Grow Blackberries Indoors for Delicious Fruit All Year
Blackberries are a delicious and nutritious snack that is relatively easy to grow, making them a great addition to any garden or landscape. When planted outdoors, you can enjoy fresh fruit in late summer and fall. However, with the right growing conditions, it is also possible to cultivate blackberries indoors and enjoy fresh fruit directly from the vine throughout the year. Below, expert berry growers share their top tips for growing blackberries indoors.
- Marvin Pritts, professor of horticulture in the School of Integrative Plant Science at Cornell University
- David T. Handley, vegetable and small fruit specialist for the University of Maine Extension
Blackberry Varieties to Grow Indoors
Most blackberry varieties listed in catalogs are not appropriate for growing indoors because they need a chilling requirement and short-day exposure to initiate flower buds, says Marvin Pritts, professor of horticulture at Cornell University.
“These plants would have to be moved outdoors in late autumn to receive shorter days and cooler temperatures, then kept in a garage or another cool place for several weeks (depending on how cold the outdoor temperature is) to receive chilling temperatures, then back inside for fruiting on the second-year canes (called floricanes).”
However, Pritts explains that some newer varieties will fruit on the first-year canes, called primocanes, and do not require chilling temperatures (between 32 and 45 degrees Fahrenheit) or short-day exposure to initiate flowering. These would include Freedom, Traveler, and Horizon from the University of Arkansas, which are the most appropriate varieties for indoor growing.
When to Plant
Light is the most limiting factor for indoor growing, so planting in spring is optimal when the most light is available, says Pritts. After fruiting, usually in late summer or early fall, cut the canes down to the top of the pot and they will regrow year-round, he explains. However, to prevent regrowth during winter when light levels are low, pots (without the canes) can be moved outside or into a garage for winter and then brought back inside in spring when light levels are higher, and growth will be better.
Care Requirements
Blackberries need optimal growing conditions in order to stay fruitful year-round indoors.
Sunlight
Full sun is best for growing blackberries indoors. Pritts recommends placing your potted fruit close to a window to ensure maximum light exposure. Aim for six to eight hours of sunlight per day.
Temperature
Indoor temperatures should range between 70 and 80 degrees Fahrenheit. “The room humidity should be relatively high during flowering so the pollen grains will germinate,” says Pritts. If the humidity is too low, the pollen grains will not germinate, and the fruits will not develop properly.
Water
As your blackberry plant grows, Pritts says it will require more water. Depending on pot size, blackberries may need to be watered once or twice daily if the container is small. “The larger the pot, the better the growth and the less watering required,” he says.
Soil
Always use a soilless potting mix when growing blackberries in pots, as regular garden soil will become too compacted. “A 2:1 blend of horticultural grade peat moss or coconut coir to pearlite has a good profile of drainage and water holding capacity for blackberry plants,” says David T. Handley, vegetable and small fruit specialist for the University of Maine Extension.
Fertilizer
Mixing a slow-release fertilizer into the potting mix before planting will ensure adequate nutrients are present to support the health and growth of your berries. Examples of slow-releasing all-purpose fertilizer blends include a mix of crustacean meal paired with langbeinite or neem cake paired with rock phosphate.
Tip
A blackberry plug refers to a young blackberry plant grown in a small soil plug. A blackberry crown is the part of the plant at ground level where the roots and the cane meet.
Container Size
The size of the container used for growing blackberries will depend on the plant size you start with, says Handley. A 1-gallon pot is typically sufficient for a small plug. However, you should replant it into a 3-gallon pot the following year. If you’re starting with a dormant crown or a long-cane plant, it’s best to plant it directly into a 3-gallon pot. After two growing seasons, the plant may need to be moved to a larger pot to ensure healthy growth.
Pollination
Obtaining pollination indoors can be challenging because there are no bees or wind to move pollen around—but you can do it by hand. Pritts recommends using a paintbrush to move pollen among the flowers, mimicking bee behavior.
Tip
Make sure to give blackberry plants enough space when growing them indoors, as blackberry canes may grow twice as long indoors than outdoors. “Canes can easily reach 15 feet or longer if not properly and regularly pinched and pruned.” Allow 4 to 5 feet between pots in a row and 8 to 12 feet between rows if growing more than a few plants.
How to Plant Blackberries Indoors
Order your plants from a trustworthy nursery when planting blackberries indoors. “Do not transplant wild blackberries from outdoors because these are almost surely infected with viruses that will reduce the health and productivity of the plants,” says Handley. Here’s what our experts say about how to plant blackberries in containers indoors.
- Place a 1-inch layer of gravel at the bottom of the pot to give it bottom weight and improve drainage.
- Pre-moisten the potting media by adding and mixing in water until you can just squeeze water out of it with your fist.
- Fill the pot halfway with potting media and place the plug or crown into the pot, and fill the rest of the pot with the media, gently firming it around the root ball or roots.
- For plugs, the media should just cover the top of the root ball; do not bury the growing point (tip) of the plant. For dormant canes, the media should just cover the top of the crown.
- Leave about a 1/2-inch space between the top of the media and the lip of the pot to prevent runoff when watering.
How to Harvest Blackberries
Blackberries are not like raspberries, which separate easily from the core when they are ripe, says Handley. With blackberries, the core remains with the fruit when harvested, so determining ripeness can be more of a challenge. As blackberries ripen, they turn from green to red to black, he says. Once they are fully black, they still need a few days to sweeten up. “The best way to tell when they are ready is when the glossiness or shine of the fruit just starts to dull a bit, and the berry separates easily from the stem or calyx.” A quick, light twist and tug should do it. If the fruit doesn’t come off easily, it’s not ready.
Blackberries will not continue to ripen once removed. The fruits should be harvested regularly once fully ripe, as they will quickly drop from the canes, says Handley. Blackberries have a very short shelf life, so refrigerate them after harvesting.
