Liquid Fertiliser for Greenhouse Tomato: A Programme for Maximum Yield Under Cover

Why greenhouse tomato needs a different fertiliser programme

Choosing and applying liquid fertiliser for greenhouse tomato is fundamentally different from open-field tomato growing. Under cover you are dealing with a heavily loaded growing system: a plant that grows for months in the same peat or substrate can draw only a limited amount of natural nutrition from it. A balanced, continuous liquid fertiliser programme is therefore essential in greenhouse tomato production.

What to look for when choosing greenhouse tomato fertiliser

Solubility and pH compatibility

In greenhouse irrigation, fertiliser is applied directly through the drip system. It must be fully soluble and have a buffering capacity that does not disturb the root zone pH (5.8–6.5). Undissolved particles block emitters and cause irrigation problems.

Nitrogen form: nitrate or ammonium?

Nitrate nitrogen should be preferred in greenhouse tomato nutrition. Ammonium nitrogen can reach toxic levels in a closed, warm and humid environment, causing root burn and stalled growth.

Rich in trace elements

The liquid fertiliser should be rich in zinc, boron, manganese, iron and copper. Greenhouse soil or substrate depletes these elements quickly.

A stage-by-stage greenhouse tomato fertiliser programme

Seedling stage (first 2 weeks after planting)

Root establishment is the priority. A balanced starter fertiliser weighted towards nitrogen and phosphorus is preferred. Fertiliser concentration is kept low (EC 1.5–2.0 mS/cm).

Vegetative growth (weeks 2–6)

The plant grows fast and leaf area expands. Nitrogen is increased; zinc and iron supplementation prevents early chlorosis. EC 2.0–2.5 mS/cm.

Flowering

Nitrogen is reduced and potassium increased. A zinc + boron combination is applied foliarly once a week · this prevents flower drop. Calcium support starts in this period; it is critical against blossom end rot.

Fruit development and harvest

Potassium and calcium are kept at their highest levels. Fertiliser concentration can rise to EC 2.5–3.0 mS/cm. As harvest approaches, nitrogen is cut back · this increases fruit sugar and aroma.

Common mistakes in greenhouse tomato growing

• Over-fertilising: keeping EC higher than necessary makes the plant run to growth and causes flower drop
• Neglecting calcium: the most frequent cause of blossom end rot is calcium deficiency or irregular irrigation
• Not monitoring pH: outside pH 5.8–6.5, fertiliser cannot be taken up even when it dissolves
• Using a single fertiliser type: the formulation should change with the growth stage

Frequently asked questions

Which liquid fertiliser is best for greenhouse tomato?

Fully soluble, nitrate-based liquid fertilisers that are rich in trace elements and pH compatible should be preferred. Casablanca meets these criteria.

When and how should calcium be applied?

Calcium should be applied foliarly every 10 days from flowering onwards. Even where calcium is supplied through the soil, a foliar application plays a supporting role under stress conditions.

How do I prevent blossom end rot?

The combination of regular irrigation and calcium supplementation prevents blossom end rot to a large extent. When the plant is short of water, calcium uptake stops · which is why continuity of irrigation matters at least as much as fertilisation.

Is foliar fertiliser safe under greenhouse conditions?

Yes, but application should be made early in the morning and the leaves dried through ventilation. Leaves that stay wet for long periods in a humid environment become more prone to disease.