Maintain mature blueberries: annual pruning

Why prune mature blueberries

A mature blueberry (Vaccinium) four years old or more no longer shoots skyward. Now yearly pruning keeps the shrub healthy, productive, and harvestable. Neglected, your blueberry grows dense, fruit shrinks, and rot sets in the inner wood. With regular pruning, you harvest thick, sweet berries every year and keep a healthy shrub for twenty, thirty years.

You prune mature blueberries differently than young ones: less hard, more selective. You maintain what you have built.

What changes in mature blueberries

Once your blueberry is four or more years old, it no longer shoots hard upward. The primary limb structure is set. What you do now is:

1. Remove old wood that no longer bears well
2. Remove diseased or damaged shoots
3. Lightly thin for air and light
4. Protect the open form

All this you do each spring (March-April) for the same harvest next year.

The spring pruning plan (March-April)

You prune your mature blueberry in March-April, just before it leafs out. This is when you best see what happened over winter.

Step 1: Remove dead and diseased

Cut all dead, frost-killed, or sickly-looking wood away to healthy tissue. Dead wood does not grow back and weakens the shrub.

Step 2: Remove old limbs (thicker than your thumb)

Blueberries bear best on wood 1-3 years old. Wood older than 4-5 years bears less fruit and grows heavy. Remove 20-30% of the oldest wood entirely to the base each year. This is called "rejuvenation."

Look at your limb structure. Which limbs are thickest (thicker than your thumb), and how old do they look? Those go out.

Step 3: Remove limbs that double or cross

If two limbs grow close together, remove the weaker. Your plant breathes better and diseases do not grow in dark inner wood.

Step 4: Lighten the base

Remove all thin, downward-growing shoots that shade the inner wood. This gives far more fruit, as berries grow better in full sun.

Step 5: Check total height

A mature blueberry may grow to 2 metres tall, but more is not needed. If you prefer harvesting at shoulder height, cut the tops back to 1.5 metres. The plant regrows fast.

Summer thinning (May-June)

In May-June you may lightly thin if you wish, but only if shoots grow outside the form. Cut these carefully. Heavy summer pruning is not advised.

Autumn inspection (September-October)

Toward season's end, walk by your blueberry and mark which limbs you will prune next March. You also spot diseases then.

Fruit thinning (optional but useful)

In May-June, as you see how many flowers you have, you may remove some young fruit. Sounds wasteful, but if you remove 20% of young berries, the remaining ones grow much larger and fuller.

Leave roughly 8-12 berries per 30 cm limb. Remove the small and weak ones.

Frequently asked questions

My blueberry bears less fruit than last year, why?

Possible causes: (1) You cut too hard last year. (2) Last season was cold and killed flowers. (3) Your blueberry's core grows too dense. (4) You have no second type (pollination needed). Check all.

How old is "old wood"?

Wood four or more years old. You see it as thick, angular limbs with deep grooves in bark. This wood bears less fruit. Remove 20-30% yearly.

Can I cut my mature blueberry back hard?

Yes, but only if truly needed (neglected or diseased). Cut everything back to roughly 50-60 cm. The plant regrows fast (2-3 years) but you miss two seasons of fruit.

What does rejuvenation mean?

Removing old wood (4-5 years or older) to the base. You force new young shoots from below. This gives more fruit and keeps your plant "young" in habit.

How do I remove thick limbs?

For limbs thicker than 2 cm, use a saw. Cut in three steps: first an undercut 30 cm from your final cut. Then cut from above until halfway through. Then make the final cut. This stops the limb from tearing.

Step-by-step

Step 1: Remove dead wood

In March, cut all dead, frost-killed, or sickly looking wood away to healthy tissue.

Step 2: Remove old wood

Remove 20-30% of the oldest wood (thicker than thumb, older than 4-5 years) entirely to the base.

Step 3: Remove doubles

If two limbs grow close together, remove the weaker.

Step 4: Lighten the base

Remove downward-growing shoots on lower wood.

Step 5: Check height

Keep your shrub to 1.5-2 metres. Cut taller tops back.

Why this works

Blueberries grow best on young wood. By removing old wood yearly, you force your plant to make new shoots. These young shoots bear much better than old, thick wood. That is the secret.

Cultivar preference

All blueberry cultivars respond the same to pruning. "Bluecrop" is most tolerant. "Duke" and "Legacy" prefer regular pruning.

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