How to prune thornless blackberries: step-by-step guide

TL;DR: Thornless Blackberry Pruning

Thornless blackberries produce fruit twice per season. In spring, remove old bare canes and let new green shoots grow. In summer, thin the green canes so they ripen evenly. Remove diseased or damaged wood immediately. This keeps your blackberries compact, healthy, and loaded with fruit.

Why prune thornless blackberries?

Thornless blackberries grow differently than spiny types. Without thorns they are friendlier in the garden, but they also grow more chaotically and wildly. Left unpruned, your blackberry patch becomes a dense tangle of knotted canes where diseases hide and harvests become difficult.

With proper pruning, you build a strong, open structure where light and air circulate. That means healthier plants, more fruit, and fewer fungal problems. Thornless blackberries respond well to pruning - they grow back vigorously and produce abundant fruit.

Year 1: Select and direct

If you have just planted thornless blackberries (in spring), start small. You may have 1 to 3 canes. In March, cut them back to roughly 60-80 cm above ground. This stimulates side shoots (laterals) to develop.

Set the plant along a trellis or wire support. Thornless blackberries grow strongly, so you need support structure. Spread the first green shoots horizontally on this trellis, not vertically. This promotes dense side growth and a compact plant.

The two-crop system

Thornless blackberries like 'Navaho' and 'Loch Ness' produce fruit at two times:

1. Summer harvest (June-July): Fruit on last year's wood (perennial canes).
2. Autumn harvest (September-October): Fruit on new wood (this season's growth).

This two-crop advantage means you do not remove everything. You keep older, fruit-bearing canes and simultaneously let new canes grow.

March pruning: The spring schedule

In March (before spring growth):

• Remove all dead, diseased, or damaged canes completely. Cut them to ground level or to healthy wood.
• Find the strongest fruit-bearing canes (last year's growth). These are usually the thickest, most vigorous stems. You can keep these.
• Cut laterals (side shoots) on these fruit-bearing canes back to roughly 30-40 cm. This encourages short fruit clusters.
• Thin out new basal shoots (those emerging from the base). Keep only the strongest 4-6. Remove thin, weak basal shoots entirely.

After March your blackberry plant looks more open and less chaotic.

June-July: Summer maintenance

In June and early July, while the summer harvest grows:

• Thin out the new green canes so they have space. Many canes together mean shade, moisture, and fungal problems.
• Let the 4-6 strongest basal shoots grow and spread them horizontally over your trellis.
• Cut green side shoots on new canes back to roughly 60 cm. This restrains overgrowth and keeps the plant more compact.
• Remove side shoots lower than 20 cm above ground - they bear little fruit and take up space.

September-October: Autumn harvest preparation

After the summer harvest (usually early August), cut the fruit-bearing canes that are now exhausted near ground level. This clears space for the autumn harvest on new wood.

The basal shoots you let grow in July will now bear autumn fruit on their side shoots. Thin them again if they are too crowded.

December-January: The major cleanup

After the autumn harvest (late October/November), conduct a thorough cleanup pruning:

• Remove all old, exhausted canes completely.
• Keep only the strongest basal shoots (now about 4-8 months old) for next summer.
• Thin these remaining canes so they grow at least 15-20 cm apart.
• Cut all side shoots on these canes back to 30-40 cm.

After this winter cleanup you are ready for next spring.

Cultivars and their behavior

Navaho: Strong grower, large fruit, both seasons reliable. Prune aggressively in March - it can tolerate it.

Loch Ness: Moderate grower, naturally more compact. Slightly more cautious with pruning - not as tolerant of hard cuts.

Chester: Very vigorous, lots of vegetation. Thin canes extra in summer. Heavy March pruning needed.

Frequently asked questions

Can I cut thornless blackberries completely after summer harvest?

No. If you remove everything, you lose the autumn harvest. The system works precisely because you keep old canes for summer while new growth emerges for autumn. Only the spent canes after summer harvest get removed.

Why is my thornless blackberry not growing after pruning?

Thornless blackberries grow vigorously, but they need nutrients. In March add compost or organic fertilizer. Also check they have enough water (especially April-May). A starving plant recovers poorly from pruning.

Can I prune thornless blackberries in autumn?

Better not until December-January. Autumn pruning before October heals poorly and diseases penetrate easily. Keep your pruning to March and December. Only emergency cuts (removing diseased canes) in between.

How many canes should I actually keep?

A mature thornless blackberry plant: 4-8 basal canes, each roughly 2-3 meters long and spread horizontally on a trellis. More canes than this creates chaos and congestion. Fewer canes (2-3) means less harvest.

Step-by-step

Step 1: March cleanup

In March remove all dead, diseased and weak wood entirely. Keep the 4-6 strongest basal shoots. Cut side shoots on fruit-bearing canes back to 30-40 cm.

Step 2: Summer thinning (June-July)

Thin out green basal shoots so the strongest grow. Spread them horizontally over your trellis. Clip green terminal shoots back to 60 cm.

Step 3: Summer harvest completion (August)

After the summer harvest, cut the spent canes to ground level. This makes room for autumn fruit.

Step 4: Winter cleanup (December-January)

Remove all spent wood completely. Keep only the strongest basal shoots. Thin to 15-20 cm spacing. Cut side shoots back to 30-40 cm.

Frequently asked questions

What if my blackberries have a lot of disease?

Remove diseased canes immediately, regardless of season. Cut to healthy wood. Disinfect your secateurs with 70% alcohol between cuts. Thornless blackberries can develop mildew if they grow too densely - prune more openly.

How much harvest do I get per plant per year?

A mature thornless blackberry plant produces 2-3 kg of fruit per season (summer plus autumn combined), with good pruning. First 2-3 years are more cautious - the plant is still establishing.

Do I need synthetic fertilizer for more fruit?

No. Compost or organic fertilizer in March is sufficient. Too much nitrogen makes excess foliage and less fruit. Keep it simple: March compost plus water plus pruning equals abundant fruit.

Are thornless blackberries really without thorns?

Yes, the canes themselves. But occasionally small thorny protrusions appear after a year or on very young shoots. Not as bad as regular blackberries, but not entirely painless.

Discover your own garden design

At [gardenworld.app](https://gardenworld.app) you can upload your front yard and see how thornless blackberries fit in your design - with realistic growth shapes and surrounding plantings. Plan and visualise before you plant your blackberry area.