Exceptionally hardy and one of the most reliable winter crops there is -- kale keeps producing edible leaves through frost that would finish off most other greens, and cold actually improves its flavour rather than ruining it. That reliability matters more than a "high in vitamin C and K" label suggests: vitamin C deficiency (scurvy) was a genuine, well-documented risk for anyone cut off from fresh food for months at a time, and it's entirely preventable with a small, steady supply of fresh vegetables. Kale is one of the few crops that keeps producing exactly when a garden needs it most -- the depths of winter, when stored calorie crops are abundant but fresh vitamin C is not.
Water need
Roots are less cold-hardy than the leaves above them -- mulch the root zone in deep cold.
Calories at a glance
490 kcal/kg -- low compared to calorie staples like potatoes or dried beans (scale is log-based across all 55 crops in the calculator, staples included, so vegetables don't all bunch at the bottom).
Temperature Range by Month
Month on the bottom, temperature up the side. The pale green background is what the plant can survive at all -- fatal above or below it, labelled directly on the chart where that applies to your zone. The coral band is its ideal range, and only fades in during the months this zone would actually have the crop in the ground -- reusing the exact same sowing/harvesting data as the calendar further down the page. The blue line is real monthly climate data (not a modelled estimate) for a representative rural/agricultural location in this zone -- a small farming town or agricultural research station rather than a major city, to avoid the warmer bias city weather stations have. For the actual verdict on how well this crop does in your zone, see the badge at the top of the page -- that's based on the site's own researched yield figures, not this chart.
Quick Start: Sowing to Harvest
- Sow. Start indoors 6-8 weeks before your last expected frost, or direct-sow once the soil is workable. Kale germinates in cool soil, down to about 4-7°C.
- Transplant & space. Move seedlings out once they have 2-3 true leaves. Give plants about 45cm (18in) of space so leaves have room to mature.
- Tend through the season. Water consistently while plants establish; once mature, kale tolerates dry spells far better than most leafy greens. Mulch protects the root zone through hard frost.
- First harvest. Begin picking outer leaves once plants reach about 20-25cm tall -- typically 55-75 days after sowing, depending on variety and climate.
- Keep harvesting through winter. Take a few outer leaves per plant at a time rather than stripping it bare, and the same plants keep producing right through frost.
Sowing & Harvesting Calendar
Pick your zone under "Temperature Range by Month" above and this updates too. The Sow row: green is the normal safe sowing window, amber is pushing the season by roughly a month either side with basic outdoor protection (cold frame, fleece, cloche), blue is starting seed indoors or under glass for an even earlier transplant. The Harvest row has two shades: solid green is the main harvest flush, while the striped tail is kale's real advantage over most vegetables -- it doesn't need lifting or storing elsewhere, so you just leave it standing and keep cutting outer leaves right through winter until it's about time to sow the next batch. Where that carries on past December, the calendar keeps going into a second year rather than cutting it off.
Calories & Yield
Kale is a nutrition and variety crop, not a calorie staple -- about 490 kcal per kg, roughly a third of what potatoes provide by weight. Grow it for winter resilience and vitamins, and let calorie-dense crops carry the bulk of your energy needs.
| Climate Zone | Yield per plant | Calories per plant | Viability |
|---|---|---|---|
| Tropical / Humid | 0.5 kg | 245 kcal | Viable |
| Subtropical | 0.6 kg | 294 kcal | Viable |
| Mediterranean | 0.5 kg | 245 kcal | Viable |
| Temperate Maritime | 0.7 kg | 343 kcal | Viable -- best zone |
| Temperate Continental | 0.6 kg | 294 kcal | Viable |
| Cool / Boreal | 0.5 kg | 245 kcal | Viable |
| Arid / Semi-Arid | -- | -- | Not viable |
| Highland / Alpine | 0.4 kg | 196 kcal | Viable |
Figures per plant sown, from the site's own crop database. Kale is the calculator's most reliable winter crop for Temperate Maritime zones specifically.
Varieties Worth Knowing
Kale varieties differ mainly in leaf shape, cold-hardiness and flavour -- some are bred for extreme winter survival, others for a milder taste or a different texture. All the varieties below are open-pollinated (OP), meaning seed saved from them breeds true and is worth keeping under this site's seed-saving approach; none are F1 hybrids.
Seed Saving -- Quick Guide
Kale crosses freely with broccoli, cauliflower, cabbage, Brussels sprouts and kohlrabi -- all one species (Brassica oleracea), despite looking nothing alike on the plate. It's biennial, needing a cold winter before it flowers.
SERVINGS, NOT DAILY CALORIES This works out plate-sized servings of kale from your seed during its fresh harvest window only, not your group's full daily calorie needs. For that, use the main calculator.
BIENNIAL Kale is a biennial, not an annual -- it doesn't produce seed in its first year. Plants grow through year one, a few overwintered plants flower and set seed in year two, and that seed is only ready to sow in year three. If you're starting from scratch with no ongoing seed supply, that means having enough seed on hand for both year one's and year two's sowing up front. Plan for roughly double the seed quantity below if that's your situation.
Estimated for your selected zone above, using this site's own germination, loss and yield figures for kale -- a helping is roughly what you'd put on a plate as part of a meal with other veg. Treat it as a planning estimate, not a promise.
Storage & Preservation
Kale isn't really a "harvest and store" crop the way potatoes or onions are -- its real storage strategy is leaving it in the ground and cutting outer leaves as you need them, right through winter. Once cut, fresh leaves only keep about 1-4 weeks depending on climate (roughly 4 weeks in cold Temperate Maritime conditions, as little as 1 week in hot Arid zones where it isn't viable outdoors anyway).
For longer preservation: blanch and freeze (the most reliable method, keeps well for months), dehydrate into kale chips, or add to ferments. Don't wait for a hard freeze to harvest everything at once -- kale's advantage over most greens is that you don't have to.
Growing Kale Without Bought Inputs
Kale attracts the usual brassica pests -- caterpillars from cabbage white butterflies, flea beetle, aphids -- but exactly which one causes trouble depends heavily on where you are, so naming "the" pest to watch for travels badly from one garden to the next. What works almost everywhere instead:
Floating row covers or fine insect netting are the single most effective input-free defence -- they physically exclude the large majority of common brassica pests regardless of which one is active locally, with no identification needed.
Companion planting helps too: aromatic herbs like dill, oregano or thyme interplanted nearby mask the scent brassica pests use to find their host, and nasturtiums nearby often draw pests away as a sacrificial trap crop.
Crop rotation matters as much as pest defence -- avoid growing kale, or any brassica, in the same bed two years running. This breaks the life cycle of soil-borne problems like clubroot, which can persist in soil for years without a host to reset the clock.
Hand-picking is a genuinely effective zero-input fallback for a small planting -- a five-minute daily check-and-squash routine keeps most infestations from ever taking hold.
Frequently Asked Questions
Is Cavolo Nero the same species as regular kale?
Cavolo Nero and ordinary Scotch/curly kale are both Brassica oleracea, the same species as broccoli, cauliflower, cabbage, Brussels sprouts, kohlrabi and purple sprouting broccoli. Red Russian and Siberian kale, however, are a different species, Brassica napus, and cross-pollinate with Swede instead. Check which type you have before saving seed.
Can I save kale seed if I'm also growing cabbage or broccoli?
Only carefully. Oleracea-type kale (Cavolo Nero, Scotch/curly) can cross-pollinate with broccoli, cauliflower, cabbage, Brussels sprouts, kohlrabi and purple sprouting broccoli if more than one is left to flower nearby at the same time. Keep varieties about half a mile (800m) apart for home use, or only let one flower per season.
How cold can kale survive?
Kale survives down to around -13°C (9°F) once established, making it one of the hardiest winter vegetables. Its ideal growing range is narrower, around 16-21°C (60-70°F), but cold doesn't just fail to kill it -- frost actively improves its flavour.
How long does kale keep after picking?
Only about 1-4 weeks fresh, depending on climate. Kale isn't a harvest-and-store crop like potatoes -- the usual approach is to leave it in the ground and cut outer leaves through winter as needed. For longer storage, blanch and freeze it or dehydrate it into kale chips.
Is kale a good calorie crop for self-sufficiency?
No -- kale provides about 490 kcal per kg, roughly a third of what potatoes give by weight. Grow it for winter hardiness, vitamin C and vitamin K, and let calorie-dense staple crops carry the bulk of a household's energy needs.
How long does kale seed stay viable?
Around 4-5 years if kept cool, dark and dry, though germination rates decline gradually each year even within that window. Test old seed before relying on it for a full planting, or sow a little extra to compensate.
Do I need pesticides to grow kale?
No. Floating row covers or fine insect netting physically exclude most common brassica pests without needing to identify which one you're dealing with, and companion planting, crop rotation and hand-picking cover the rest for a home-scale planting.