Brussels Sprouts – Pruning and Topping

If you’re growing Brussels sprouts you’re obviously already a lover of this much maligned Brassica. I grow some each year although nobody else in the house eats them, to me Christmas dinner just feels wrong without a few sprouts on my plate and I love the taste. I’ve noticed that the majority of seed websites show sprout plants with their leaves removed to reveal large tender sprouts, I’ve also heard allotment folk recommend leaf removal to each other, but is this leaf pruning necessary or purely for packaging?

Firstly I think you have to consider the purpose of a leaf – leaves photosynthesise sunlight to produce energy so that food can be made for the growing plant, water, nutrients, CO2 etc. Removing leaves unnecessarily will logically reduce the available energy put into the development of the plant and its sprouts. In that regard I think we can assume that removal of too many Brussels sprout leaves is not going to ‘stimulate growth’ as some suggest, quite the opposite in fact.

Why removing sprout leaves might have some benefits:

• Removing leaves reduces the overall weight of a Brussels sprout plant, this helps reduce ‘wind rock’ and keeps the plant more stable. Even staking sometimes isn’t enough to keep a tall and heavy plant upright in a winter gale. Wind rock can disturb the plants and make the individual sprouts ‘blow’ – flower early.
• Too many overlapping leaves in tightly packed rows of sprout plants will potentially reduce air flow. This could provide wetter conditions – perfect for fungal diseases like downy mildew, or for slugs and snails to thrive.
• It’s possible that as an individual sprout grows larger on the main stem it may be inhibited from increasing in size by the leaf branch growing immediately beneath it (what a lovely problem to have!)

My Sprout Pruning Rules

More yellow leaves removed

As a Brussels sprout plant grows taller, the lower leaves will turn yellow anyway because the individual sprouts mature from the bottom up. Any yellowing leaves should be removed by hand. Yellow leaves will otherwise fall of their own accord and this will attract slugs and snails which may then breed and/or go on to attack the healthy leaves and sprouts on the plant above. Typically I remove the yellow leaves on a weekly basis and also any that are seriously damaged by pests on lower levels. My Brassicas are always netted to keep out pheasants but a Cabbage White butterfly always finds a way in through the holes too. You never see the caterpillars but you see the damage!

Typically once a sprout plant has around 10 rows of sprouts growing on its stem I will remove yellow leaves AND one extra row of leaves above that per week. This has always worked for me and gives me some of the benefits identified above without harming the plant’s ability to photosynthesise too much. When a sprout plant has reached a good height of around three feet and is covered in growing sprouts I cut off the very top.

Topping a Brussels sprout plant

Topping produces more equal sprout sizes

Topping a Brussels sprout plant forces all the energy to go into the existing sprout growth without harming the plant’s ability to keep photosynthesising. The sprouts are more likely to grow quickly and to an even size, rather than maturing quickly at the bottom of the stem and more slowly at the top. Perhaps this is the beneficial confusion that has crept into the idea that we should strip side leaves off? If possible I aim to top my first Brussels sprout plants in October, with a view to them getting through one or two light frosts to improve the flavour before harvest. If you’re growing from F1 seeds it may not be necessary to wait for a frost to sweeten the flavour because they may have already been grown for a sweeter taste.

A Related Anecdote

When my son was three years old I was sitting in the living room watching TV to hear my mother-in-law shout “Matt, is Jake meant to be doing that?!” I looked out of the window to see the boy standing at the bottom of the garden beside my Brussels Sprout plants (before my allotment days). He was clutching a small red plastic seaside spade and was violently slashing all the sprout leaves off. I quickly (and somewhat angrily) intervened but the damage was done, leaves were scattered all over the floor. The stems were fine, as were the sprouts, but they provided a pitiful sight on the plate come Christmas day. I now know from experience  that removing too many Brussels sprout plant leaves is definitely not recommended!

How the commercial farmers harvest their Brussels Sprouts in the US: