Kale earns its place in a British vegetable garden because it can keep producing useful leaves when many summer crops have finished. It tolerates cold weather well, looks attractive in a mixed border and can be grown either for full-sized cooking leaves or for tender baby leaves. Most growing problems begin with cramped plants, poor protection from cabbage pests or starting too late for plants to establish before winter.
You don't need to grow a field of kale. Two or three healthy plants can provide regular pickings for a household that uses it occasionally. For salads, a short row of closely spaced young plants may be more practical than several large specimens.
Choose the right type of kale
Curly kale has ruffled leaves that hold up well in soups and hearty dishes. Cavolo nero, sometimes called Tuscan kale, carries long, narrow, dark leaves with a textured surface. Red-leaved varieties can look striking against winter greens. Differences aren't purely decorative: varieties also vary in mature size, cold tolerance and suitability for baby-leaf harvesting.
Read the packet before buying. A compact kale can fit in a generous patio pot, while a tall variety may occupy a substantial area for much of the year. If you want harvests in deep winter, choose a variety described as suitable for overwintering. If you're growing kale for salad, look for varieties with pleasantly tender young leaves.
The Royal Horticultural Society notes that kale is a member of the brassica family. This matters when planning a vegetable plot, because broccoli, cabbage, sprouts and kale can share pests and soil-borne diseases.
When to sow kale seeds
Spring and early summer are the usual sowing periods for crops that will mature towards autumn and winter. Sowings can be made directly into a prepared bed or started in seed trays or modules and planted out later. Follow the calendar on your specific variety, as baby-leaf and large winter crops have different aims.
For indoor sowing, fill clean modules with peat-free seed compost, water lightly and sow seeds at the depth directed on the packet. Give the seedlings good light once they emerge. Avoid leaving plants in small cells until their roots are densely tangled; pot them on or plant out when conditions allow.
For outdoor sowing, make a shallow drill in firm, prepared ground. The RHS describes sowing kale about 1cm deep. Water dry soil first, sow thinly and mark the row so you can distinguish emerging kale from weeds. Young seedlings attract slugs, snails and sometimes flea beetles, so inspect them frequently.
If sowing in the final position, thin seedlings to the spacing recommended on the packet. For larger plants this may be 45–60cm or more, depending on variety, whereas leaves intended for early cutting can be grown much closer together. Crowding a full-sized winter variety reduces airflow and makes it harder to reach the lower leaves.
Preparing soil and planting out
Kale likes fertile, moisture-retentive but free-draining soil. It can tolerate light shade, although a sunny position is helpful in the shorter days of autumn. Remove perennial weeds before planting, since extracting their roots between established kale stems is awkward.
Work well-rotted garden compost into the planting area if the soil needs improvement. Alternatively, use a no-dig approach, adding compost as a surface mulch. Avoid turning fresh manure directly against young roots.
When transplants are sturdy enough to handle, harden off plants raised indoors. Water the modules before removal and make holes deep enough to place plants firmly, with lower leaves just above soil level. Brassicas appreciate firm soil: a plant rocking in the wind often struggles to establish. Water in thoroughly and check the plants during the first dry spell.
If you have previously had clubroot in the plot, the site deserves special attention. Clubroot affects brassica roots and can persist in the soil. Growing healthy transplants, improving drainage and rotating crops can help reduce risk, but a badly affected bed may be unsuitable for susceptible brassicas for many years.
How to grow kale in a pot
Kale is a good container crop if you choose the right size. For one compact mature plant, the RHS suggests a pot around 30cm wide and deep. Larger varieties may need more room. Use peat-free multipurpose compost and a container with drainage holes.
Set the pot where it receives useful light and won't topple in winter winds. Compost in containers dries out faster than soil in a bed, particularly when a large plant has filled the pot with roots. Check moisture below the surface and water when necessary, allowing surplus water to drain. In prolonged wet weather, make sure drainage holes have not become blocked.
Baby-leaf kale is particularly straightforward in containers. Sow a small patch fairly closely, then pick young leaves while tender. You won't achieve the same large plant as you would with wider spacing, but that may be an advantage on a balcony.
Protect kale from caterpillars and pigeons
Brassica pests can wreck a crop surprisingly quickly. White butterflies lay eggs on cabbage-family leaves; their caterpillars then feed on the plants. Pigeons may tear substantial pieces from unprotected foliage, especially as other food becomes scarce.
Fine insect-proof mesh secured over hoops is one of the most useful measures. Install it early rather than after holes begin appearing. The mesh should not lie directly on the foliage, and there should be no easy gaps around the edges. Check underneath occasionally: a trapped pest can still cause damage.
Use sturdy netting supports because mature kale plants become tall, particularly on exposed sites. Make certain birds cannot become entangled in loose netting. Slugs and snails can still attack young seedlings under covers, so ground-level checks remain worthwhile.
Watering, feeding and supporting growing plants
Once plants are established in fertile garden soil, kale is not especially demanding. Water in prolonged dry spells, particularly while leaves are expanding rapidly. A compost mulch can help retain moisture and suppress weeds.
Do not assume yellowing leaves always mean a shortage of fertiliser. Lower leaves age naturally, and waterlogging, pests or root disease can create similar symptoms. Examine the growing conditions before feeding. In relatively poor soil, a feed suitable for leafy vegetables may be worthwhile when plants are actively growing, using the product instructions.
Tall winter kale can rock in strong wind. A stout cane and a soft tie, or a little soil firmed around the base, may protect the stem and roots. Put supports in before winter gales arrive rather than waiting for a plant to lean sideways.
When and how to harvest kale
The most useful feature of kale is repeated harvesting. Once a plant is well established and carrying plenty of healthy foliage, take a few lower leaves at a time. Leave the central growing point and the younger upper leaves in place so the plant can continue producing.
For full-sized varieties, pick sound leaves before they become tough or badly weathered. Examine the undersides for insects and wash thoroughly before cooking. If you want salad leaves, harvest them young, when the texture is more tender.
The RHS describes autumn, winter and spring cropping from suitable varieties. Growth slows during very cold, dark periods, so don't expect midwinter regrowth at summer speed. Plan your picking around what is already on the plant rather than stripping it bare on one day.
Kale can be steamed, sautéed or added to soups and stews. Removing the thickest parts of the central rib from large leaves can make the finished dish more pleasant. Baby leaves need less cooking.
Common problems with kale
Leaves full of holes: Look for caterpillars or slugs and check the effectiveness of your mesh. Small holes may be only cosmetic, but defoliation can slow the plant considerably.
Plants looking weak and stunted: Examine drainage, spacing and root health. Persistent swelling or distortion of roots can indicate clubroot rather than a simple nutrient deficiency.
Purple or yellow lower foliage: Some colour is normal for particular varieties and for ageing leaves. If discolouration spreads rapidly, review watering, frost damage and possible pests.
Plants collapsing in wind: Firm the soil and support tall stems. An established plant with loosened roots can suffer even when it hasn't snapped.
Slow winter growth: This is largely seasonal. Established leaves can remain harvestable while new growth is limited by cold and short daylight hours.
What to do at the end of the crop
As plants finally run to flower or lose quality in spring, remove spent stems and clear away diseased material. Healthy residues can be composted appropriately, but avoid spreading roots from plants suspected of clubroot around your plot. Move the next brassica crop to a different bed where practical.
Kale succeeds when it is allowed to become a strong, well-spaced plant before winter and is protected from common pests. Sow at the appropriate time, keep the roots healthy and pick outer leaves steadily. The reward is a fresh crop precisely when the vegetable garden can otherwise feel rather empty.
Source
Royal Horticultural Society, How to Grow Kale.