How to Water and Feed Kale for Tender Leaves

Kale is a nitrogen crop, and it keeps asking

Unlike a fruiting crop, everything you harvest from kale is leaf, and leaf is built from nitrogen. A plant you pick from for six months will strip a bed that was well fed at planting by around midseason. The signal is unmistakable: the oldest leaves at the bottom go uniformly pale yellow while the growing point stays green, because the plant is dismantling old leaves to feed new ones.

Work two to three inches (5 to 8 cm) of compost into the bed before planting, then side dress with a nitrogen-leaning granular feed every three to four weeks once the plant has eight true leaves. A handful scattered in a ring six inches (15 cm) out from the stem and scratched in is the whole job. In containers, switch to a liquid feed at half strength every week instead, because watering flushes the nutrients straight out.

Water to a depth of an inch, not to the surface

Kale leaves that turn tough and leathery are almost always a watering problem rather than an age problem. When the soil dries and rewets in big swings, the plant thickens its cell walls and the leaves become fibrous. Steady moisture gives you leaves you can eat raw. Push a finger in: if it is dry at one inch (2.5 cm), water; if it is still cool and damp, leave it.

In open ground a mature plant wants roughly one inch (2.5 cm) of water a week including rainfall, delivered in one or two soakings rather than a daily sprinkle. Shallow daily watering keeps the roots in the top two inches of soil, which is exactly where they are most vulnerable in a hot spell. Water the soil at the base in the morning and keep it off the foliage, since wet leaves overnight invite downy mildew.

1. Test at one inch before every watering Push a finger into the soil beside the plant, not right at the stem. Dry at that depth means water. Damp means wait, even if the surface looks parched.
2. Soak, then leave it Give enough that the water reaches six inches (15 cm) down, which is roughly two gallons (8 liters) per square foot of bed for most soils. Then do not water again until the finger test says so.
3. Water in the morning at the base Morning watering lets the foliage dry before nightfall. Hold the can low and put the water on the soil, not over the leaves.
4. Mulch two inches deep Straw or leaf mold two inches (5 cm) deep, kept clear of the stem itself, halves how often you need to water and keeps the soil temperature steady.

Strip the lower leaves and keep the stem clean

Kale grows from a single central point, adding new leaves at the top while the lowest ones age out. Once a bottom leaf yellows it is no longer feeding the plant, it is a landing pad for aphids and a bridge for slugs, and it holds moisture against the stem. Snap it off sideways at the base every time you visit.

Doing this all season leaves you with a bare, palm-like stem and a rosette of good leaves on top, which is exactly what you want. Air moves freely under the canopy, you can see the soil to check for slug damage, and every leaf on the plant is one you would actually eat.

1. Remove anything yellow or holed Take off every leaf that has gone yellow, been shredded by caterpillars, or is lying on the soil. Bend it sideways and down and it snaps at the base cleanly.
2. Never strip above the growing point Leave at least eight healthy leaves in the rosette at the top. Strip below that and the plant stalls, because it no longer has the leaf area to feed new growth.
3. Take the leaves off the bed Old brassica leaves left on the soil carry downy mildew spores and shelter slugs. Bag them or compost them well away from the row.

Once the bare stem is more than about a foot (30 cm) long, tall plants get top heavy and rock in wind, which tears the roots. Either earth up around the base or push in a short cane and tie the stem loosely.

Cold weather changes the care routine

As temperatures drop the plant slows down and its needs change completely. Growth roughly halves below 50F (10C) and effectively stops below 40F (4C), so a plant that wanted feeding every three weeks in autumn wants nothing at all in deep winter. Feeding a dormant kale just pushes soft growth that the next freeze will damage.

Watering also drops away sharply. In cold, still weather a plant may go two or three weeks between waterings, and the commonest winter mistake is drowning a kale that was never thirsty. Keep the finger test and ignore the calendar entirely.

What to note down as you go

Kale is a long crop and it is easy to lose track of what you did to it. The three things worth writing down are the dates you fed it, the date you first saw aphids or caterpillar damage, and the date the leaves first tasted sweet after a cold night. Those three between them tell you almost everything you need to change next season.

Add the position of each plant in the bed if you have several. Brassicas should not follow brassicas in the same ground for three years because of clubroot, and a note of where the row ran is far more reliable than memory once the bed has been dug over twice.

1. Log each feed on the day you do it A dated note stops the two commonest errors at once: forgetting for six weeks, and feeding twice in ten days because you were not sure.
2. Note the first pest sighting The date the first cabbage white butterfly appears over the bed is remarkably consistent year to year. Next season you will know when to get the netting on.
3. Mark where the row ran Sketch the bed with the row positions. It is the only practical way to keep a three year brassica rotation honest.