Fertilising guide

How to fertilise Spinach (Spinacia oleracea)— schedule & NPK

Also called true spinach, flat-leaf spinach, savoy spinach.

About Spinach

Spinacia oleracea · also called true spinach, flat-leaf spinach · edible

Spinach is a cool-season leafy green that bolts quickly in heat. Best sown in early spring and autumn for tender leaves; New Zealand spinach (Tetragonia) substitutes well in hot summers. Pet-safe in small amounts; large amounts can be problematic for some pets.

Spinacia oleracea is a cool-season crop native to southwest Asia, first cultivated in Persia (Iran) over 2000 years ago.

A heavy feeder: fertilize before planting and again at midseason (e.g. about ¼ lb 5-10-5 per 10 ft of row when plants are ~2 in tall).

Growth habit: Low rosette annual

Watch for — Yellow leaves: Nitrogen deficiency or downy mildew.

Sources: hort.extension.wisc.edu, extension.psu.edu, plants.ces.ncsu.edu

What fertiliser spinach actually wants — and why

Spinach 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 spinach: 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 spinach, 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 spinach:

A nitrogen-leaning feed every 3-4 weeks while harvesting. 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 spinach 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 spinach

Use the vegetable-feed label rate for spinach. 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 spinach first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the spinach watering schedule.

Signs you are over-feeding spinach

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

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 spinach

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 spinach care brief covers soil, humidity and the common problems for this species.

Flushing and leaching the salts

For container-grown spinach, 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 spinach

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 spinach — frequently asked questions

What fertiliser does spinach 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. Spinach 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 spinach?

A nitrogen-leaning feed every 3-4 weeks while harvesting. A nitrogen-leaning feed every 3-4 weeks while harvesting. 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 spinach?