How to Grow Brassicas

To avoid any build-up of pests or diseases, brassicas should not be planted immediately after other brassicas. They will succeed best when the soil is firm and not too acidic. It should also be fertile, though not recently manured.

Ideally, use ground that was manured for a previous crop and then dug and, if necessary, add lime conditioner to the soil in the autumn or early winter. If it was not manured for a previous crop, then some garden compost or well-rotted manure (such as Orgro) should have been incorporated when it was dug.

Remove any weeds or surface debris and rake in some general-purpose fertiliser, such as Growmore, but avoid forking it over immediately before planting.

When to Sow Brassicas

When you sow brassica seeds depends on the type and cultivar of brassica. Specifically, early crop brassicas are sown between February and April, main crop brassicas between March and May and overwintering brassicas between May and June. The seed packet of your chosen variety will provide the best recommendation.

How to Sow Brassicas

Brassicas can be sown either outdoors in a seedbed when the soil is warm or indoors to protect them from pests and cold weather.

If sowing indoors, you should sow your seeds in seed trays, with one seed per module. They can be started on a warm, sunny windowsill or in a cold frame or greenhouse as long as daytime temperatures stay between 10–20°C (50–68°F) and are covered with insulation on cold nights. 

If sowing outdoors in a seedbed, sow seeds thinly, 1.25cm (½in) deep, in rows spaced 15cm (6in) apart. Once your seeds have germinated, thin them to 7.5cm (3in) between each plant.

Your seedlings should be transplanted to their final growing site once they’re sturdy enough to handle. Water the day before you move them, and keep your plants well watered until they’re established.

When to Plant Out Brassicas

Brassicas are recommended to be planted out depending on their type or variety. However, many brassicas can be planted out between late spring and early summer after being hardened off.

Spring or autumn crops like cabbage seeds, broccoli seeds or cauliflower seeds will mature relatively quickly after planting. Winter crops, such as Brussels sprouts seeds or kale seeds, will take much longer to mature outdoors.

How to Plant Brassicas

Use a garden line to ensure rows are straight when planting brassicas. Make holes, with Darlac hand tools such as a trowel or dibber, at the correct spacings (see the chart below) and, after inserting the plants, firm them in well.

After planting, give them a thorough watering to ‘puddle’ them in. Do this carefully to make sure the roots are not disturbed. If the soil is very dry, it is a good idea to fill planting holes with water and allow this to drain before putting in the plants.

Plant Spacing for Brassicas

Depending on the type you choose when growing brassicas, each requires different spacing to ensure ample room for them to grow and good airflow between plants. The recommended plant spacing for the different types of brassicas is as follows:

Cabbage Collars

Cabbage collars are an effective method of pest control to prevent the problem of cabbage root fly from developing. They protect the base of the plant from adult flies laying eggs near them. In addition, they can be useful in suppressing weed growth and keeping soil warm and moist for fast establishment. They are not just useful for cabbages but can be used when growing cauliflower plants, broccoli plants, and Brussels sprouts plants.

As an alternative to purchasing cabbage collars, you can cut your own collars from materials such as roofing felt or carpet underlay.

Watering

You should keep your brassicas well watered in dry spells, particularly in the first month after planting.

Weeding

To reduce competition for nutrients, weeds should be removed using weed control products such as a hoe or weed by hand.

Mulching

Adding a layer of organic matter as a mulch around your brassicas, such as well-rotted manure or garden compost, will keep the soil moist, provide nutrients and prevent weeds from developing.

Feeding

When growing brassicas, adding an occasional liquid fertiliser, such as Natura Grow, during the summer will boost the crop.

When to Harvest Brassicas

Harvest time will depend on when you have grown your brassicas. Generally, cauliflower, broccoli, kohl rabi and summer cabbages should be ready for harvest from July onwards.

How to Harvest Brassicas

When harvesting brassicas, you should harvest gradually if possible. For example, kale and sprouting broccoli are cut-and-come-again plants, meaning that they will continue to produce leaves or heads again once picked. This will provide you with plenty of produce over an extended period.

Some brassicas, such as Brussels sprout and turnip plants, are not only cold-hardy but can even benefit from a frost. Harvesting certain brassicas after a frost can improve the flavour, as the frost causes the plant to convert its starches into sugars.

For harvesting all brassicas, you should do so early in the morning when the crops will be most crisp, fresh and flavoursome. This is because later in the day, plants will lose water through transpiration and use sugars from photosynthesis for growth, causing a slightly less sweet and vibrant flavour.

Brassicas are often chosen by gardeners as most varieties are easy to grow and typically problem-free. However, there are some issues that they can face. Below are the most common and methods of either preventing or resolving them:

Pests: Collectively, brassicas are vulnerable to a range of pests, such as caterpillars and aphids. One of the most bothersome is the cabbage root fly, which can attack cabbages and several other brassica plants.

If you put on a covering of Enviromesh UV30 Fleece to deter cabbage root fly, this will also keep off many other pests. You can also use cabbage collars to protect against cabbage root fly as described above under Plant Care. Otherwise, keep a watch for any pests and pick them off or use pest and disease control products, such as bug spray, if necessary.

Birds: Birds, specifically pigeons, are known to attack brassica plants. Where bird damage is a problem, and you are not protecting plants with Enviromesh, cover them with some bird-proof garden netting, at least until they are established.

Wind rock: Some brassicas can be vulnerable to wind rock, which is when roots are loosened as a result of winds, impacting your plants’ growth and yield. To prevent this, ensure to press the soil firmly when planting your brassicas and apply an organic mulch. Some taller brassicas, such as Brussels sprouts and kale, may need staking in exposed positions.

To get started on growing your own brassica plants, we have a diverse selection of brassica seeds and brassica plants at D.T. Brown to choose from. You can find a vast range of different cultivars for all types of brassicas, allowing you to enrich your cooking with exceptional flavours that can’t be found in supermarkets.

In addition to our many brassica guides, you can find plenty more advice to get your growing space thriving with our garden blog. As well as growing guides for vegetable seeds and fruit seeds, you can find many more articles with general tips to keep your garden flourishing all year round.

If you’d like to know more about our selection of herb seeds, flower seeds, garden equipment, or any of our other garden supplies, get in touch with us today and a member of our team will gladly help you.