Why Is My Broccoli Stem Hollow?

Cutting into a broccoli stem to find a hollow cavity running through the centre is alarming, but it is a common occurrence and in most cases the broccoli is still perfectly edible. The hollow develops during rapid growth and is almost always linked to either a boron deficiency or conditions that cause the plant to grow faster than its tissues can properly fill. Understanding which is responsible helps prevent it in future seasons.

Boron deficiency

Boron is a micronutrient that plays a role in cell wall development and the movement of sugars within plants. When boron is deficient, rapidly growing tissues cannot form properly and a hollow, sometimes brown-tinged cavity develops in the stem. Boron deficiency is most likely on very alkaline soils (pH above 7.5), on sandy soils that have been heavily watered or rained on (boron leaches easily), or in gardens where excessive lime has been applied. A soil test will confirm low boron levels.

Too-rapid growth

Even with adequate boron, broccoli that grows very quickly — after a sudden flush of warm weather, or following heavy nitrogen feeding — can develop hollow stems simply because the outer tissues grow faster than the interior can fill. This is sometimes called pithiness. The stem may appear slightly spongy rather than truly hollow. Avoiding large nitrogen applications mid-season and maintaining consistent rather than burst-heavy watering reduces the incidence of pithiness.

Is hollow-stemmed broccoli still safe to eat?

Yes — unless the hollow is accompanied by browning, softness or an off smell, the head and stem of hollow broccoli are perfectly edible. The texture and flavour of the head are usually unaffected. Remove any brown or deteriorating tissue and use the rest.

Fixing boron deficiency

Apply borax (sodium tetraborate) to the soil before planting at roughly 35g per 10 square metres, worked in well. Alternatively, use a diluted foliar borax spray (a quarter teaspoon per litre) at planting and again a month later. Be cautious about overdosing — excess boron is toxic to plants. A pH of 6.5–7.0 maintains good boron availability without needing supplementation on most soils.