Blackberry in Zone 7B — Pacific Northwest

Blackberries offer a rewarding experience for the Pacific Northwest gardener. The taste of a sun-ripened blackberry, especially after our cool nights, is unmatched, and they're incredibly versatile for jams, pies, or just eating fresh. Plus, the satisfaction of harvesting your own berries is hard to beat.

We do face some unique challenges here in the PNW, like cool soil in spring and the potential for late blight to affect nearby plants. However, with a bit of planning and attention to timing within our 193-day growing season, you can absolutely enjoy a bountiful blackberry harvest.

Transplant your blackberry canes outdoors from mid-April through mid-May. This gives them a good head start after the last frost, but before the dry summer months fully kick in. Remember to harden off your bare-root canes or potted plants for about a week before planting. Gradually expose them to outdoor conditions to prevent shock.

Space your plants 3-5 feet apart, allowing plenty of room for their vigorous growth. Keep an eye on the weather forecast during this period. We often have overcast spring days and occasional chilly snaps, so protect your young plants if a late frost is predicted. Blackberry care is very similar to raspberries, so if you have experience with those, you're already ahead of the game.

Blackberries need consistent moisture, especially during their fruiting period, but they don't like soggy feet. Once established, blackberries are more drought-tolerant than raspberries, but don't neglect them during our dry summer months. Mulching heavily around the base of the plants helps retain moisture and suppress weeds.

During our wet springs, you may not need to water at all, but once the dry summer kicks in, check the soil regularly. Use the finger test: stick your finger about 2 inches deep into the soil near the base of the plant. If it feels dry, it's time to water. Aim for about 1-2 inches of water per week, depending on rainfall. Water at the base of the plant to avoid wetting the foliage, which can encourage fungal diseases in our sometimes humid conditions.

Signs of underwatering include wilting leaves and dry, shriveled berries. Overwatering can lead to yellowing leaves and root rot. Adjust your watering schedule accordingly.

Blackberries are vining plants with vigorous canes, so a strong trellis system is essential. A simple wire trellis works well, with horizontal wires strung between sturdy posts. Install the trellis before or at the same time you plant your blackberries to avoid disturbing the roots later.

Train the canes to grow along the wires, tying them loosely with twine or plant ties. This will keep the berries off the ground, improve air circulation, and make harvesting much easier. Thornless varieties are particularly easy to manage on a trellis.

Pruning is key to maintaining healthy and productive blackberry plants. After harvest, remove the spent floricanes (the canes that produced fruit) completely, cutting them back to the ground. These canes will not produce again.

During the growing season, tip-prune the new primocanes (the current year's growth) at about 4-5 feet to encourage branching. This will result in more fruiting laterals and a heavier crop next year. As our first frost approaches in late October, stop pruning to allow the plants to harden off for winter.

You can expect your first blackberry harvest from mid-June through early August, depending on the variety and the specific weather conditions that year. Blackberries are ready to pick when they are fully black, not dark red. They should pull off the cane easily without squeezing them. A dull surface, rather than a shiny one, also indicates full ripeness.

Harvest gently to avoid damaging the berries or the plant. Blackberries don't ripen off the vine, so only pick the ones that are truly ripe. To encourage continued production, harvest regularly, every few days, removing any overripe or damaged berries. As the first frost approaches in late October, harvest any remaining ripe berries, even if they are slightly underripe. They can be used for jams or other cooked preparations.

Here are some common problems you might encounter with blackberries in the Pacific Northwest:

Spotted Wing Drosophila

• What it looks like: Tiny fruit flies laying eggs inside ripening berries, causing them to become soft and mushy.
• What causes it: These flies thrive in our mild, humid summers.
• How to fix/prevent it: Use netting to exclude the flies from your plants. Apply organic insecticides, such as spinosad, according to label instructions. Harvest berries frequently to remove potential breeding grounds.

Cane Blight

• What it looks like: Canes develop brown or purple lesions that girdle the stem, causing it to wilt and die.
• What causes it: Fungal disease that enters through wounds in the canes, often after pruning. Wet springs and overcast spring days encourage fungal growth.
• How to fix/prevent it: Prune in dry weather to minimize the risk of infection. Sterilize your pruning tools between cuts. Remove and destroy infected canes promptly.

Orange Rust

• What it looks like: Bright orange pustules appear on the undersides of leaves in spring. Infected canes become stunted and unproductive.
• What causes it: Systemic fungal disease that overwinters in the plant.
• How to fix/prevent it: Remove and destroy infected plants completely. There is no cure for orange rust. Choose disease-resistant varieties.

Japanese Beetles

• What it looks like: Metallic green beetles that skeletonize leaves and feed on flowers and fruit.
• What causes it: These beetles are becoming increasingly common in the PNW.
• How to fix/prevent it: Handpick beetles off plants and drop them into soapy water. Use traps to attract and kill beetles (place traps away from your blackberry plants). Apply neem oil to deter feeding.

Pacific Northwest Specific Challenges: Our mild heat and dry-summer rainfall can create favorable conditions for some pests and diseases, while also limiting the spread of others. Monitor your plants regularly and take action quickly to prevent problems from escalating. Late blight is a concern for tomatoes and potatoes, so plant blackberries away from these crops. Slugs can also be a problem, especially in wet springs, so use slug bait or other control methods.

Companion planting can help improve the health and productivity of your blackberries.

Good companions:

• Tansy: Repels Japanese beetles and other pests.
• Garlic: Deters aphids and other insects.
• Green Beans: Fix nitrogen in the soil, benefiting the blackberry plants.
• Mint: Can deter some pests, but be careful, as it can be invasive.

Bad companions:

• Tomato, Pepper, Potato: These plants are susceptible to late blight, which can also affect blackberries.