Blackberry in Zone 7B — Desert Southwest

Blackberries offer a taste of summer sweetness that's hard to beat, and they are surprisingly well-suited to our Desert Southwest gardens. Imagine fresh blackberry jam made with fruit you grew yourself, or a refreshing blackberry lemonade to beat the extreme heat. Plus, their vigorous growth fills a trellis beautifully.

While our climate presents challenges like intense sun and alkaline soil, blackberries are more forgiving than some other berries. By planting at the right time and providing consistent care, you can enjoy a bountiful harvest within our long, 245-day growing season.

Transplant your blackberry plants outdoors from mid-March through mid-April, after the last threat of frost has passed. Before planting, harden off your bare-root canes or potted plants by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the intense Desert Southwest sun.

Space plants 3-5 feet apart to allow for ample growth. Be mindful of late-season temperature swings that can occur at this time. If a late cold snap is predicted, protect your young plants with frost cloth.

Blackberries need consistent moisture, especially during fruiting, but they're more drought-tolerant than raspberries once established. In our arid Desert Southwest climate, regular watering is essential.

During the hot summer months, water deeply about 2-3 times per week, providing roughly 1-2 inches of water each time. Use the finger test – if the soil is dry 2 inches below the surface, it's time to water. The monsoon season can supplement your watering schedule, but don't rely on it entirely.

Water at the base of the plant to avoid wetting the foliage, which can encourage fungal diseases in our warm nights. Overwatering can lead to root rot, indicated by yellowing leaves, while underwatering results in dry, brittle foliage. Mulch heavily around the base of your plants with wood chips or straw to help retain moisture and regulate soil temperature.

Blackberries are vining plants and need a strong trellis system to support their vigorous growth. A sturdy wire trellis or fence works best, allowing the canes to be trained and supported as they grow.

Install your trellis before or at the time of planting to avoid disturbing the roots later. Train the canes along the trellis wires, spacing them evenly to allow for good air circulation and sun exposure. Thornless varieties are easier to manage on a trellis.

Blackberry pruning is relatively simple. After harvest, remove the spent floricanes (the canes that produced fruit) down to the ground. These canes won't produce again.

During the growing season, tip-prune new primocanes (the current year's growth) at about 4-5 feet to encourage branching and more fruit production. As the first frost approaches in mid-November, you can lightly prune any overly long canes to prevent wind damage.

Your first blackberry harvest in the Desert Southwest can typically be expected from mid-May through early July, about 60 days after transplanting. Look for fully black berries that have a dull surface – this indicates they are ripe and ready to pick.

The berries should pull easily from the plant without squeezing. Avoid picking berries that are still dark red, as they are not fully ripe. Harvest regularly to encourage continued production. As the first frost nears, harvest any remaining ripe berries, even if slightly underripe; they can be used for jams or pies.

Here are some common problems you might encounter with blackberries in the Desert Southwest:

Spotted Wing Drosophila

• What it looks like: Small, soft-bodied flies lay eggs in ripening fruit, causing it to become soft and mushy. You might see tiny larvae inside the berries.
• What causes it: This pest thrives in warm, humid conditions, though the Desert Southwest’s monsoon season can provide enough moisture for them to become active.
• How to fix/prevent it: Use fine netting to cover your plants, and promptly remove any infested fruit. Insecticidal soap can also be effective.

Cane Blight

• What it looks like: Dark brown or black lesions appear on the canes, often near pruning cuts or injuries. The affected canes may wilt and die back.
• What causes it: A fungal disease that enters through wounds in the canes, often exacerbated by excessive humidity or overhead watering.
• How to fix/prevent it: Prune out infected canes at the base of the plant and dispose of them properly. Avoid overhead watering and ensure good air circulation.

Orange Rust

• What it looks like: Bright orange pustules appear on the undersides of leaves and young shoots. The plant may become stunted and unproductive.
• What causes it: A systemic fungal disease that infects the entire plant.
• How to fix/prevent it: Remove and destroy infected plants. There is no cure for orange rust, so prevention is key. Choose disease-resistant varieties.

Japanese Beetles

• What it looks like: Metallic green beetles skeletonize leaves, leaving a lacy appearance.
• What causes it: These beetles are attracted to the foliage and fruit of blackberry plants.
• How to fix/prevent it: Handpick beetles off the plants and drop them into a bucket of soapy water. Use insecticidal soap or neem oil as needed.

Desert Southwest Specific Challenges: The extreme heat and intense sun can stress blackberry plants, making them more susceptible to pests and diseases. Consistent watering and afternoon shade are crucial for summer survival. The monsoon season can bring much-needed moisture, but it can also increase the risk of fungal diseases. Ensure good air circulation and avoid overhead watering to mitigate these risks.

Good companions for blackberries in the Desert Southwest include tansy, garlic, green beans, and mint. Tansy repels many common pests. Garlic deters borers. Green beans fix nitrogen in the soil, benefiting the blackberry plants. Mint can help suppress weeds, but be sure to contain it, as it can be invasive.

Avoid planting tomatoes, peppers, and potatoes near blackberries. These plants are susceptible to similar diseases, which can spread between them. Also, potatoes are heavy feeders and can deplete the soil of nutrients that blackberries need.