Blackberry in Zone 7A — Pacific Northwest

Blackberries are a rewarding addition to any Pacific Northwest garden. Their sweet, tangy flavor shines in jams, pies, and eaten fresh off the vine. Plus, with our cool nights and mild summers, the flavor of homegrown blackberries is truly exceptional.

While we might not have the scorching heat of other regions, you can absolutely grow blackberries here. Our 183-day growing season gives you plenty of time for a successful harvest. Just be mindful of our wet springs and plan accordingly.

You can transplant your blackberry canes outdoors from mid-April through mid-May, after the last expected frost. Before planting, be sure to harden off your young plants by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the sun and wind.

Space your blackberry plants 3-5 feet apart to allow for ample growth. Keep an eye on the weather forecast – those overcast spring days can still bring a late cold snap. Protect your young plants with row covers if necessary.

Blackberries need consistent moisture, especially during their fruiting period, but they aren’t fond of soggy roots. While they are more drought-tolerant than raspberries once established, don't let them dry out completely during our dry summer months.

During our wet springs, you likely won't need to water much at all, letting the rain do the work. However, once the dry summer months arrive, check the soil regularly. Use the "finger test" – stick your finger about 2 inches deep into the soil. If it feels dry, it's time to water. Aim for about 1-2 inches of water per week, delivered at the base of the plant to avoid wetting the foliage.

Signs of underwatering include wilting leaves and dry, shriveled berries. Overwatering can lead to yellowing leaves and root rot. Mulching heavily around your blackberry plants with wood chips or straw helps retain moisture and suppress weeds, which is especially helpful during our drier summers.

Blackberries are vigorous vines that need strong support to thrive. A sturdy trellis system is ideal, providing a framework for the canes to climb and preventing them from sprawling all over your garden. This also makes harvesting much easier.

Install your trellis before you plant your blackberries to avoid disturbing the roots later. A simple wire trellis with posts works well. As the canes grow, train them along the wires, tying them loosely with garden twine. Thornless varieties are much easier to manage on a trellis!

Pruning is essential for maintaining healthy and productive blackberry plants. After harvest, remove the spent floricanes (the canes that produced fruit) at the base. These canes won't produce again.

During the growing season, tip-prune the new primocanes (the current year's growth) at about 4-5 feet tall. This encourages branching, which leads to more fruit the following year. As the first frost approaches around mid-October, there's not much to do besides a final tidy-up of any dead or diseased foliage.

In the Pacific Northwest, you can expect your first blackberry harvest from mid-June through early August, depending on the variety and the weather. Blackberries are ready to pick when they are fully black, not dark red, and pull off the vine easily without squeezing. A dull surface, rather than a shiny one, is another sign of full ripeness.

Gently grasp the berry and pull it straight off the stem. Avoid tugging or squeezing, which can damage the plant and the fruit. Blackberries don't ripen off the vine, so only pick the ones that are truly ready.

Blackberry plants will produce continuously over several weeks. Keep harvesting regularly to encourage continued production. As the first frost approaches in mid-October, harvest any remaining ripe berries. Any green berries won't ripen.

Here are some common issues you might encounter with blackberries in the PNW:

Spotted Wing Drosophila

• What it looks like: Tiny, clear punctures in the berries, often leading to soft, rotting fruit.
• What causes it: This invasive fruit fly lays its eggs inside ripening fruit. Our mild summers and wet springs create ideal conditions for them.
• How to fix/prevent it: Use netting to exclude the flies. Apply organic insecticides labeled for SWD control, following the instructions carefully. Remove and destroy any infested fruit promptly.

Cane Blight

• What it looks like: Dark brown or purplish lesions on the canes, often near pruning cuts or injuries. The canes may eventually die back.
• What causes it: A fungal disease that enters through wounds in the canes. Wet weather, especially during pruning, favors its spread.
• How to fix/prevent it: Prune during dry weather. Disinfect your pruning tools between cuts. Remove and destroy any infected canes. Ensure good air circulation around the plants.

Orange Rust

• What it looks like: Bright orange pustules on the undersides of the leaves. Severely infected plants may be stunted and unproductive.
• What causes it: A systemic fungal disease that infects the entire plant. Spores are spread by wind and rain.
• How to fix/prevent it: Remove and destroy any infected plants immediately. There is no cure for orange rust. Choose resistant varieties when possible.

Japanese Beetles

• What it looks like: Metallic green beetles that feed on the leaves and flowers, causing significant damage.
• What causes it: These invasive beetles are attracted to the foliage and can quickly defoliate plants.
• How to fix/prevent it: Handpick beetles off the plants and drop them into a bucket of soapy water. Use row covers to protect plants. Apply organic insecticides labeled for Japanese beetle control.

Pacific Northwest Specific Challenges: Our mild heat means blackberries ripen slower than in hotter climates, so patience is key. Our dry-summer humidity helps prevent some fungal diseases, but be vigilant about cane blight after pruning. The dry-summer rainfall patterns mean you'll need to monitor watering closely during the fruiting season to ensure a good harvest.

Companion planting can benefit your blackberries in the Pacific Northwest.

Tansy repels many insect pests, acting as a natural deterrent. Garlic helps to deter pests and may also help to prevent fungal diseases. Green beans fix nitrogen in the soil, which can benefit blackberry growth. Mint attracts beneficial insects and can help to deter pests, but be sure to contain it, as it can be invasive.

Avoid planting blackberries near tomatoes, peppers, and potatoes. These plants are susceptible to late blight, which can also affect blackberries. Additionally, they compete for the same nutrients in the soil, potentially hindering blackberry growth.