Fertilising guide

How to fertilise Redbor Kale (Brassica oleracea var. sabellica 'Redbor')— schedule & NPK

Also called Redbor kale, red curly kale, ornamental red kale.

More about redbor kale

About Redbor Kale

Brassica oleracea var. sabellica 'Redbor' · also called Redbor kale, red curly kale · edible

'Redbor' is a tightly curled F1 kale with striking deep magenta-purple, frilly leaves on a tall stem, equally at home in the vegetable plot and the ornamental border. The colour deepens and intensifies in cold weather, and the leaves sweeten after frost. Like all curly kales it is a hardy, heavy-feeding cool-season biennial, very frost-tolerant and at its best from autumn through winter.

Growth habit: Tall, upright, non-heading biennial grown as an annual, with a single stout stem bearing a dense crown of tightly curled leaves; pick lower leaves and it continues to produce from the top.

Watch for — Wind rock: Tall plants on loose soil rock in wind, loosening roots and stunting growth. Plant firmly and deeply, earth up the stem, and stake exposed plants.

What fertiliser redbor kale actually wants — and why

Redbor Kale is grown entirely for its leaves, so nitrogen is the priority — steady, nitrogen-leaning feeding keeps it growing fast, tender and unbolted.

For the language behind the three numbers on the bottle — what nitrogen, phosphorus and potassium each do — see the NPK ratio explained entry. The short version for redbor kale: match the feed to the job the plant is doing right now, not to a generic “plant food” on the shelf.

How often to feed redbor kale, and which months

Feeding only earns its keep while the plant is in active growth and can use the nutrients — pour feed into a dormant or low-light plant and it simply builds up as root-burning salt. For redbor kale:

A hungry crop. Enrich the bed with compost or aged manure before planting and side-dress or liquid-feed with a nitrogen-rich fertiliser every 3-4 weeks; steady feeding sustains the dense curly leaf production. In practice: a balanced or compost-rich start, then a nitrogen side-dress or liquid feed every 3-4 weeks through the cropping period in the main season (spring through early autumn).

The dormant-season rule matters more than the exact interval: skip feeding entirely when redbor kale is resting. For the wider context on indoor feeding rhythms across the seasons, the houseplant fertiliser schedule walks through the year month by month.

What strength to mix for redbor kale

Use the vegetable-feed label rate for redbor kale. Steady availability matters more than a strong dose — a check in growth makes leaves tough and can trigger bolting.

Feeding always goes onto already-damp soil, never dry roots — water redbor kale first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the redbor kale watering schedule.

Signs you are over-feeding redbor kale

Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for redbor kale:

Very soft, floppy, dark-green growth that attracts aphids.
Excess leafy growth at the expense of hearts/heads in cabbage and the like.
Salt crust and scorched leaf edges in containers; nitrate-heavy leaves.

Signs you are under-feeding redbor kale

Pale, yellow-green leaves, oldest first, and slow growth.
Small, tough, bitter leaves and premature bolting.
Weak, stunted heads in cabbage, broccoli and cauliflower.

If the symptoms point at watering, light or roots rather than nutrition, the full redbor kale care brief covers soil, humidity and the common problems for this species.

Flushing and leaching the salts

For container-grown redbor kale, water until it drains freely each time and flush pots monthly with plain water to stop nitrogen salts accumulating; in the ground, good compost levels naturally buffer this.

Organic vs synthetic feeds for redbor kale

Organic options

Well-rotted manure or compost dug in, plus nitrogen-rich liquid feeds like diluted chicken-manure pellets or nettle feed. UK: pelleted chicken manure or Westland; US: Espoma Garden-tone or blood meal. Steady and soil-building.

Synthetic / liquid feeds

A balanced feed at planting then a high-nitrogen liquid or granular side-dress — UK: Growmore then a nitrogen feed or Phostrogen; US: a 10-10-10 then a high-N (e.g. 21-0-0) side-dress or Miracle-Gro.

Brand names are examples, not endorsements, and UK and US ranges differ — check the label’s own NPK and dilution rate, since formulations change.

Fertilising redbor kale — frequently asked questions

What fertiliser does redbor kale need?

A nitrogen-leaning feed (higher first number) or compost-rich soil — nitrogen drives the fast, tender leafy growth this crop is grown for. Phosphorus and potassium matter far less here than for fruiting crops. Redbor Kale is grown entirely for its leaves, so nitrogen is the priority — steady, nitrogen-leaning feeding keeps it growing fast, tender and unbolted.

How often should I feed redbor kale?

A hungry crop. Enrich the bed with compost or aged manure before planting and side-dress or liquid-feed with a nitrogen-rich fertiliser every 3-4 weeks; steady feeding sustains the dense curly leaf production. A hungry crop. Enrich the bed with compost or aged manure before planting and side-dress or liquid-feed with a nitrogen-rich fertiliser every 3-4 weeks; steady feeding sustains the dense curly leaf production. In practice: a balanced or compost-rich start, then a nitrogen side-dress or liquid feed every 3-4 weeks through the cropping period in the main season (spring through early autumn).

What strength of feed for redbor kale?