Brussels sprouts

Methods for propagating Brussels plants are similar to broccoli, as in the previous lesson; also to kale, autumn cabbage and all larger brassica plants. Here I shall add a few small differences to that general process for raising brassica plants.

• Seeds germinate almost immediately in warmth and appear within three to six days from sowing.

Sowing conditions

Under cover is definitely best because you are doing all of this work in the spring, when insects such as flea beetle are very common. Also you will probably be using expensive hybrid seed, some of which, if sown outside, will be eaten.

Sowing time

Seed packets suggest sowing from early spring, and this is possible. However, it precludes the possibility of any preceding vegetable in the same bed. It also gives earlier harvests, which you may not want.

My best sowing date is early May, which give transplants of a good size by the middle of June. Space is then appearing among vegetables that were sown in early spring and are now ready to be cleared. Brussels plants still have time to grow large, and give harvests a little later, which is worthwhile if overall you want a long season of fresh harvests.

Sowing method

With the aim of one plant per module, sow in a small tray and prick out within a week. Module size can be 3–4 cm/up to 1.5 in diameter.

Pot on?

A slightly later transplant date allows the first vegetable (carrots in this case) to grow more. Therefore moving/potting the module plants into 7 cm/3 in pots after around four weeks is highly worthwhile. This gives another two weeks of growth for both carrots and Brussels, before transplanting.

‍

The photos below show how I transplant Brussels sprouts in a bed of carrots. There are other possible vegetables you could grow as first plantings, such as lettuce and salad onions.

It has often been claimed that brassica plants do not use mycorrhizal networks for their growth. I disagree with this, based on my observations since 1983:

• The success of these interplantings suggests that the carrots are helping their mates the Brussels.
• Brassica plants generally give bigger harvests on the no dig bed of my two trial beds, compared to the dig bed. In the dig bed, mycorrhizal networks are broken every December by my digging, and perhaps the brassicas miss them. Or perhaps there are other differences that favour the no dig brassicas, such as bitter soil aggregation. Read more on this Trials page.

Interplanting

This carrot/Brussels method came about when I was harvesting carrots in June 2015, and I had nowhere to plant my Brussels which were ready to go in the ground. I planted them amongst the carrots and it worked exceptionally well.

I had done something similar long before:

• In 1983, during my first year of market gardening, I transplanted lettuce among newly planted Brussels sprouts. I also grew an equivalent bed of the same sowing of Brussels sprout plants, without any lettuce. The bed with lettuce grew much stronger plants of Brussels sprouts.

New plantings of brassicas are often far apart, and few transplants like being so distant from any other plant. Almost any vegetable or flower nearby can help the new transplants, partly through mycorrhizal networks (just as long as the neighbours are not large plants, which may suck out all the moisture.)

Carrots work well because, from a sowing at spring equinox, they are within a month of finishing by mid-June. It’s straightforward to harvest a few carrots in order to create space for each Brussels transplant.

Transplant size

The height of plants can be 12–18 cm/5–9 in, growing in modules and pots respectively. Use a dibber or trowel to make holes, and bury the stems as much as you can when popping in the plants.

Transplant time

This depends on your sowing time, and is four to six weeks from that date. Aim to set plants in the ground any time from mid-spring to early summer, and no later than that.

Spacing

Best spacing is wide enough to grow plants of a large size when mature. Then you can enjoy sprouts of reasonable size themselves.

• Allow 50–60cm/20–24 in – I suggest the wider distance of those two.
• Wide spacing also means that plants have more chance to find sufficient moisture in summer, which reduces the likelihood of aphids.

Support

This may or may not be necessary, partly depending on whether you mind the plants leaning onto a pathway. My photos below show how they can still grow and crop while leaning, and this involves much less work than staking.

A wooden stake for each plant is the most thorough and reliable way to hold them upright. Use stout string to tie the main stem to the stake, at one or two heights.

Brussels plants grow best when there is a constant supply of moisture in the soil. They do not perish in dry conditions, but simply suspend much new growth until water arrives through rain or watering.

How often

In the summer, give just enough water to keep them growing strongly, which may be once a week in dry conditions. If it is still dry when they start cropping, give water twice a week.

How much

Large amounts of water may be needed because they are large plants, and fast-growing until mid-autumn! This is weather dependent, and the leaf colour is an indicator. If you notice a matt hue to leaves, this suggests your plants need quite a lot of water.

Extra mulch to retain moisture?

This is worthwhile in dry climates, and you can water through it as well. Remember that mulches of undecomposed material can prevent summer rainfall from passing into the soil, unless it rains a lot.

‍

This is not only about size, because the first few Brussels at ground level are very small and never grow large, however long you wait. Therefore pick them off in early autumn. They are tasty, if not too pest-eaten.

At the other end of the season, a bonus harvest is the ‘sprout tops’, the cluster of leaves at the highest point. As plants mature through autumn and winter, these head leaves lighten in colour, fold inwards and start to look like a loose-leaved cabbage, but are more tender and sweet.

• They are a true delicacy. However, once harvested, the Brussels plants cannot grow anymore. I hesitate to eat the tops for this reason, and usually only do so from January onwards.

How to judge readiness

After the first pick of baby sprouts, you are watching for the ones further up to swell and change colour slightly, from a darker to paler green. If left unpicked for long after this, you will see some splitting, browning and probably also pest damage.

It’s worthwhile picking sprouts regularly, a few off each plant, as long as it’s in season. This catches them before they show decay, such as yellowing of the outer leaves, which lengthens preparation time before cooking.

How to pick

With your thumb on top of the sprout you want to pick, and fingers underneath it, push firmly downwards until it detaches from the main stem.

Always pick the lowest sprouts on each stem. This means that you are pushing down into free space, and they are easier to snap off. The stem of each sprout is impressively strong.

When to pick and how often

Through autumn it works well to pick a few sprouts off each plant, once a week.

In cold winter weather, the harvest interval may be two to three weeks.

Storing

It’s often cool after you harvest Brussels sprouts, and you can keep them outside in the shed for a week or two easily – the cooler the better. They are not damaged by freezing, rather it sweetens them.

Saving seed

As for broccoli, this is a huge job in terms of space needed, and also of plant selection. I have never done it and would seek the advice of professionals.

Which pests are likely, and when

These are the same as for broccoli and I mention extra details here, relating to Brussels sprouts.

• Aphids are common on any plants with signs of weakness, which can be rectified in the long term by improving soil health and fertility, through applications of compost mulch. Watering can help too if it’s dry.
• Usually, the biggest problem is pigeons eating leaves, because Brussels are there for them in winter months when they are hungriest.

Protections needed

For a bed width of 1.2 –1.5m/4–5 ft, a piece of mesh 3.6m/12 ft wide is your best investment. This protects new plantings from insects, as well as the preceding carrots for example. Its width allows plants to grow quite tall before you need to remove it, which is as soon as you see the sides lifting above ground level.

Thereafter, proceed as for broccoli, with perhaps Bacillus against caterpillars (or rub them off), and probably an overhead piece of netting in the winter.

Other likely difficulties, including disease

Sprouts that do not fold in tightly are described as ‘blown’, with a rosette of open leaves. Plants that grow like this will probably never make tight buttons of Brussels sprouts, and it’s a fault of bad varietal maintenance. Some old-fashioned varieties that used to grow firm Brussels sprouts now do not, hence my recommendation of hybrids.

Clubroot is possible – see Lesson 5 on broccoli. If you know your soil to have clubroot spores, it may not be worth growing Brussels sprouts because they are a large investment of time and effort, which would be quite a loss if growth is very poor.

In temperate climates with sufficient moisture, and when soil is fertile, there should be few problems with disease. You may find the odd sprout goes mushy, the odd plant may suffer from grey aphids or its growing point may decay, but overall these are strong, healthy plants. Removing lower leaves is major prevention against diseases such as Alternaria.

Alternaria leaf spot (Alternaria brassicae)

This can affect any plant of the brassica family. It occurs mainly in late summer and autumn, after periods of rain, with temperatures around or above about 18°C/64°F.

It appears as dark circular spots, which increase in size, sometimes with concentric rings inside and a yellow halo outside. It is common on older leaves of Brussels sprouts for example.

• Regular twisting or breaking off of older brassica leaves, and removing to the compost heap, is your best control. Use gentle downward pressure on each leaf, even if still mostly green.

‍