How to Grow Kale Organically
Quick answer
Growing kale organically mostly comes down to prevention. Move kale and other cabbage-family crops to a new spot every year. Extension advice ranges from a 3-year rotation to a 5–7-year one where clubroot is in the soil. Put floating row cover over the bed at seeding or transplanting and seal the edges. Kale doesn’t need pollinators, so the cover can stay on all season—lift it briefly to pick leaves, then reseal the same day if you still need exclusion. Check leaves weekly and catch caterpillars while they’re small, either by hand or with Bt, which caterpillars have to eat to be affected. For fertility, work compost into the soil before planting and let a soil test guide what else you add (UMD rates leafy greens as a medium feeder at the general vegetable nitrogen rate). Harvest outer leaves while the center keeps growing—a cut-and-come-again crop that can run well past the first fall frosts. Kale and turnip greens can tolerate about 15–20°F (UMD). For shared Acephala timing and spacing while a dedicated grow-kale page is still missing, see how to grow collards and the ZIP planting calendar.
Updated
The sections below cover cole-crop rotation year counts (shown separately, not averaged), season-long row cover, Alternaria, black rot and clubroot, organic fertility at UMD’s medium leafy-greens rate, and pests — with Acephala timing on the collards grow guide until a dedicated kale grow page exists.
Related: how to grow collards (closest Acephala grow page) · organic cabbage · organic broccoli · cabbage-family companions.
Diseases
- Alternaria: “Alternaria is a common disease that causes spots on leaves.”
- Black rot: “Black rot causes yellow triangles on the edge of leaves.”
- Clubroot: “Clubroot attacks the roots of kale and collards”.
UMN Extension, Growing collards and kale
UMN also notes bitter or pungent flavor when plants are overheated or struggling to take up water — steady moisture and cool weather keep leaves tender.
Crop rotation: how many years?
Rotation years disagree — do not average. Use the longer band if clubroot is in the soil.
| Source | What it says | Context |
|---|---|---|
| Penn State | No cole crop where a brassica grew the previous year; three-year rotation is best | Home garden, general |
| UMass (black rot / Alternaria) | At least three years with non-cruciferous crops; control cruciferous weeds | Black rot; Alternaria |
| UMN | At least four years without related cole crops | General cole-crop diseases |
| UMass (clubroot) | Long 5–7 year rotations between brassica crops | Clubroot in the soil |
UMN: grow where you have not grown cabbage-family crops for the past four years (UMN Extension; UMN Brussels sprouts). UMass: brassica weeds harbor flea beetles and cut the value of rotation (UMass Extension).
Black rot and Alternaria (cultural)
Start with certified disease-free seed or transplants. UMass: sanitation, avoid prolonged leaf wetness, rotate, control cruciferous weeds (UMass black rot; UMass Alternaria). Bactericides are only marginally effective for black rot.
Hot-water seed treatment
UW–Madison Extension lists hot-water seed treatment for black rot of crucifers (UW–Madison Extension). Test a small sample for germination first if you treat seed at home.
Clubroot (cultural)
Worse on cold, wet, acidic soils; long-lived spores. Cultural steps (UMass): lime per a soil test, 5–7 year brassica rotations, drainage, weed control, clean transplant media (UMass Extension).
Fertilizer and rates
Organic fertility only on this page. No synthetic side-dress N-P-K formulas.
UMD: “Fertilizer needs: Medium requirement for nutrients, either from soil organic matter or fertilizers. Use starter fertilizer when transplanting, side-dress three weeks later.” “Incorporate compost into the soil before planting.” (UMD Extension, Growing Leafy Greens) UMN: “If you use manure or compost, you may not need additional fertilizer applications, depending on how much organic matter you apply.”
Organic nitrogen rate (UMD): “The general N recommendation for vegetable crops is 2 pounds per 1,000 square feet”. UMD’s cottonseed meal (6-2-1) example: “2.0 ÷ 0.06 = 33.3 pounds of cottonseed meal fertilizer per 1,000 square feet”. (UMD, Fertilizing Vegetable Gardens)
Organic nitrogen sources UMD names include cottonseed meal (6-2-1), blood meal, fish meal, and fish emulsion. UMD: “Don’t fertilize too early in spring, since cool soil temperatures limit nutrient release from organic matter.” Use as the label directs. See organic fertilizer basics.
Frost timing
There is no dedicated /grow/kale/ page yet. For shared Acephala timing and spacing, see how to grow collards (same UMN collards-and-kale source family). Use the ZIP planting planner and frost dates for frost-based windows.
Harvest (cut-and-come-again)
Pick outer leaves and leave the center growing (UMN, Clemson, NC State). UMD’s cut-and-come-again method for thickly sown salad greens: cut to the crown at about 6–10 inches; regrowth is ready again in about 2–3 weeks if watered and fertilized. UMD: kale and turnip greens “can tolerate temperatures of 15 - 20°F.”. UMN: plants continue to grow past the first fall frosts; frost can sweeten leaves (Clemson, NC State).
Pests to watch for
Controls and bee cautions are on our pest page; follow the links rather than repeating spray schedules here.
Row covers
Fit covers at seeding or transplanting and seal the edges (UMN, UMass). UD: “Row covers can be left on all season for crops that don’t require insect or wind pollination, including beans, brassicas (cabbage, kale, broccoli, brussels sprouts etc.), and potatoes.” (UD Cooperative Extension). Lift briefly to harvest, then reseal the same day if you still need exclusion.
Caterpillars and Bt
UMN: treat while caterpillars are still small. Scout both sides of leaves weekly; handpick into soapy water; if needed, Bt — “Caterpillars must eat it to be effective. Get good coverage on the leaves when spraying.” (UMN Extension). Follow the label. Cabbage worms on the pest page.
Flea beetles and aphids
UMN: treat seedlings at more than about five flea beetles per plant; summer treatment usually isn’t needed once plants reach the 4–5-leaf stage (UMN Extension). Kale’s waxy leaves are less attractive than mustard greens (UMass, Clemson). Aphids: encourage predators with flowering plants; knock aphids off with a strong jet of water (UD). Insecticidal soap is among labeled options — follow the label; choose OMRI-listed products when you spray. See soap vs neem vs oil.
- Cabbage worms: green caterpillars chew holes in leaves.
- Flea beetles: tiny beetles pit young leaves with shot holes.
- All cole-crop pests: the cole crop list on the pest page.
Related cole crop: how to grow cauliflower.
Frequently asked questions
How long should I rotate kale?
Penn State says never in the same spot two years running, and three years is best. UMass says at least 3 years for black rot and Alternaria. UMN says four years without cole crops. UMass says 5–7 years where clubroot is present. Do not average those bands.
Can I leave row covers on kale all season?
Yes. UD Extension says row covers can be left on all season for crops that don’t require insect or wind pollination, including brassicas (cabbage, kale, broccoli, brussels sprouts etc.). UMN says to remove them after harvesting the crop. Lift briefly to pick leaves, then reseal the same day if you still need exclusion.
How do I harvest kale so it keeps producing?
Pick outer leaves and leave the center growing (UMN, Clemson, NC State). UMD’s cut-and-come-again shear method for thickly sown salad greens: cut to the crown at 6–10 inches; regrowth is ready again in about 2–3 weeks if watered and fertilized.
What's the organic way to stop cabbage worms on kale?
Use row cover from seeding or transplant day, check both sides of leaves weekly, and handpick into soapy water. If you still need more, Bt works on small caterpillars, which must eat it (UMN).
Does Bt spare beneficial insects?
UMN says a Bt product is highly effective on small caterpillars, while preserving the parasitoids and natural enemies you will need for season-long control. Follow the label.
How cold-hardy is kale?
UMD: kale and turnip greens can tolerate temperatures of 15–20°F. UMN: plants will continue to grow and produce new leaves well beyond the first fall frosts, and leaves can be harvested even after they’ve frozen. Clemson and NC State note frost sweetens the leaves.
How do I prevent black rot and Alternaria organically?
Start with certified disease-free seed or hot-water-treated seed, avoid overhead watering on wet plants, remove infected seedlings, rotate, and control mustard-family weeds (UMass). Sanitation and environmental management are the main tools.
What causes clubroot, and how do I avoid it?
A soil organism with long-lived spores. It’s worse in cold, wet, acidic soils. Keep the pH up with lime per a soil test, improve drainage, rotate 5–7 years, and don’t move infested soil (UMass).
What organic fertilizer does kale need?
Work in compost or well-rotted manure, test your soil, then use UMD’s general rate of 2 lb nitrogen per 1,000 sq ft if needed (UMD rates leafy greens as medium feeders). Use starter fertilizer at transplant and side-dress three weeks later (UMD). UMD’s published cottonseed-meal example is 33.3 lb per 1,000 sq ft at the 2 lb rate. No synthetic side-dress formulas on this page.
How many flea beetles is too many?
UMN says to treat seedlings at more than five per plant, and that summer treatment usually isn’t needed once plants reach the 4–5-leaf stage. Kale’s waxy leaves are less attractive than mustard-family greens (UMass, Clemson).
How do I manage aphids on kale organically?
Encourage predators with flowering plants; knock aphids off with a strong jet of water (UD). Insecticidal soap is among the labeled options — follow the label; choose OMRI-listed products when you spray. See soap vs neem vs oil.
More organic guides: Organic gardening hub · Organic pest control · Organic fertilizer.
Sources
- University of Minnesota Extension: UMN Extension, Growing collards and kale; UMN Brussels sprouts; UMN Extension; UMN Extension
- UMass Extension: Brassica flea beetles; UMass black rot; UMass Alternaria; Brassicas clubroot
- University of Wisconsin–Madison Extension: UW–Madison Extension
- University of Maryland Extension: UMD Extension, Growing Leafy Greens; UMD, Fertilizing Vegetable Gardens
- University of Delaware Cooperative Extension: UD Cooperative Extension