Fertilising guide

How to fertilise Tomato (Solanum lycopersicum)— schedule & NPK

Also called garden tomato.

About Tomato

Solanum lycopersicum · also called garden tomato · edible

Tomato is a warm-season fruiting crop from the Andes, the cornerstone of the home vegetable garden. It needs 6-8 hours of direct sun, consistent water, and steady feeding to set heavy fruit. Foliage and stems are mildly toxic to pets if eaten in quantity.

Solanum lycopersicum is an edible crop in the nightshade family (Solanaceae); its wild red-fruited ancestor Solanum pimpinellifolium originates in the Andean region of western South America (Peru and Ecuador), with domestication tied to agricultural societies from Peru to pre-Columbian Mexico.

It is a heavy feeder, but extension sources recommend fertilisers lower in nitrogen and higher in phosphorus (numbers like 4-12-4 or 5-20-5) and adequate calcium, since excess nitrogen promotes leafy growth at the expense of fruit and worsens blossom-end rot.

Growth habit: Determinate (bush) or indeterminate (vine) annual

Watch for — Yellow lower leaves: Early blight, nitrogen depletion, or natural senescence.

Sources: hort.extension.wisc.edu, inspection.canada.ca, britannica.com

What fertiliser tomato actually wants — and why

Tomato feeds in two distinct phases — balanced to build the plant, then high-potassium the moment flowering starts to set and fill a heavy crop.

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 tomato: 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 tomato, 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 tomato:

Balanced feed at planting; switch to a higher-potassium feed (tomato food) once flowering starts. So: a balanced feed or compost at planting, then a high-potash liquid every 1-2 weeks from first flower through harvest across the main season (spring through early autumn).

The dormant-season rule matters more than the exact interval: skip feeding entirely when tomato 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 tomato

Follow the crop-feed label rate for tomato — these are calibrated for hungry vegetables. Consistency through fruiting matters more than strength; erratic feeding causes problems like blossom-end rot.

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

Signs you are over-feeding tomato

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

Vigorous dark-green leafy growth but few flowers or fruit (excess nitrogen).
Lush foliage hiding the crop; soft growth prone to pests and disease.
Salt crust on the soil and scorched leaf edges in containers.

Signs you are under-feeding tomato

Pale, yellowing lower leaves and stunted growth.
Small fruit, poor set, and a quickly exhausted plant.
Blossom-end rot and weak cropping from erratic or insufficient feeding.

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

Flushing and leaching the salts

In containers, fertiliser salts build up fast — water tomato thoroughly so excess drains from the base each time, and flush pots with plain water every few weeks to prevent a damaging salt build-up.

Organic vs synthetic feeds for tomato

Organic options

Garden compost or well-rotted manure dug in before planting, plus a liquid comfrey or seaweed feed once fruiting starts. UK: comfrey feed or organic Tomorite; US: Espoma Tomato-tone or Neptune's Harvest. Builds soil and feeds in one.

Synthetic / liquid feeds

A balanced feed at planting then a high-potash tomato feed in fruiting — UK: Growmore at planting then Tomorite (Levington) or Phostrogen; US: a balanced 10-10-10 then Miracle-Gro Tomato or a bloom booster.

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 tomato — frequently asked questions

What fertiliser does tomato need?

Balanced (even N-P-K) at planting for roots and frame, then switch to a high-potassium ("high-potash") tomato-style feed once the first flowers open — potassium is what sizes and ripens fruit, not nitrogen. Tomato feeds in two distinct phases — balanced to build the plant, then high-potassium the moment flowering starts to set and fill a heavy crop.

How often should I feed tomato?

Balanced feed at planting; switch to a higher-potassium feed (tomato food) once flowering starts. Balanced feed at planting; switch to a higher-potassium feed (tomato food) once flowering starts. So: a balanced feed or compost at planting, then a high-potash liquid every 1-2 weeks from first flower through harvest across the main season (spring through early autumn).

What strength of feed for tomato?

What does over-feeding tomato look like?

Vigorous dark-green leafy growth but few flowers or fruit (excess nitrogen). Lush foliage hiding the crop; soft growth prone to pests and disease. Salt crust on the soil and scorched leaf edges in containers. Staying on a high-nitrogen feed once tomato starts flowering is the classic error — you get a huge leafy plant and a disappointing crop. Switch to high-potash the moment flowers appear.

Should I flush the soil of tomato?