Prime-Ark 45 Blackberries

Prime-Ark® 45 Thorny Blackberry 

Prime-Ark® 45 is a high-performing, thorny, erect blackberry variety developed by the University of Arkansas. Known for its large, flavorful berries and excellent productivity, this variety is unique for producing fruit on both first-year canes (primocanes) and second-year canes (floricanes), giving growers an extended harvest season.

Floricane fruit typically ripens from early to mid-June, while primocane fruit begins maturing in late summer and can continue into fall until frost. The berries are large, firm, and sweet with classic blackberry flavor, making them ideal for fresh eating, baking, preserves, and freezing.

Prime-Ark® 45 is a dependable choice for both home gardeners and commercial growers seeking high yields, an extended harvest window, and adaptability to a range of growing conditions.

Mature Size: 4–6 ft. tall
Spacing: 3–4 ft. apart
Harvest Season: Early summer and again late summer through fall
Growth Habit: Erect canes (thorny)

Growing Information

USDA Hardiness Zones: 5–9
Sun Exposure: Full sun (6–8+ hours daily for best fruiting)
Soil Type: Well-drained, loamy soil
Soil pH: Slightly acidic (ideal range 6.0–6.8)

Watering

Keep soil consistently moist, especially during flowering and fruit development. Provide about 1–2 inches of water per week. Water deeply rather than frequently and avoid soggy conditions, as blackberries do not tolerate standing water.

Sunlight

Full sun is essential for maximum berry size, sweetness, and yield. In very hot climates, light afternoon shade can reduce plant stress, though heavy shade will reduce production.

Fertilizing

Feed plants to support vigorous cane growth and heavy fruiting:

• Early Spring (as new growth begins): Apply a balanced fertilizer such as 10-10-10 at a rate of ½ cup per plant, spread in a circle 12–18 inches from the crown. Water thoroughly after application.

• Late Spring to Early Summer (after the first flush of flowering or early harvest): Apply a lighter feeding of ¼–½ cup per plant to support continued primocane growth and fall fruiting.

Compost or well-aged manure may also be used. Avoid excessive nitrogen, which encourages leafy growth at the expense of fruit.

Pruning

Prime-Ark® 45 fruits on both floricanes (second-year canes) and primocanes (first-year canes).

• After early summer harvest: Remove spent floricanes at ground level
• During summer: Tip primocanes when they reach about 3–4 ft. tall to encourage branching
• Late winter: Shorten side branches (laterals) on primocanes to 12–18 inches to improve fruit size and manage plant shape
• Remove weak, damaged, or overcrowded canes to improve airflow

What does “tipping” mean?
Tipping simply means cutting off the top 1–2 inches of a young, upright cane once it reaches about 3–4 feet tall. This stops the cane from growing taller and signals the plant to produce side branches (laterals). These side branches are where many of the berries will form, leading to higher yields and a more manageable plant.

Laterals are the shorter side branches that grow from the main upright canes and are where much of the fruit develops.

Harvesting

Prime-Ark® 45 provides two harvest periods:

• Floricane crop: Early to mid-June

• Primocane crop: Late summer through fall until frost

Berries are ripe when fully black, glossy, and detach easily with a gentle pull. Harvest every few days during peak production. Refrigerate promptly and use within several days, or preserve by freezing, canning, or making jams.

Propagation

Blackberries can be propagated by tip layering or root cuttings.

Tip layering:

1. In late summer, select a long, flexible primocane.

2. Bend the cane tip to the ground and bury it 2–3 inches deep.

3. Keep soil moist while roots develop.

4. Once rooted, sever from the parent plant and transplant.

Root cuttings:

1. During dormancy (late fall or early spring), dig a healthy root about the thickness of a pencil.

2. Cut into 2–4 inch sections.

3. Plant horizontally in well-drained soil, covering with about 1 inch of soil.

4. Keep lightly moist until shoots emerge, then transplant once established.

Plant Quality

Our Prime-Ark® 45 blackberry plants are propagated from tissue culture stock. This process helps produce clean, uniform plants with reduced risk of disease and strong, vigorous growth from the start.