Best Liquid Fertilizers for Tomatoes

Tomatoes are heavy feeders. They need calcium for cell walls (no calcium, hello blossom end rot), potassium for fruit set, magnesium for chlorophyll, and a steady stream of nitrogen for foliage. The right liquid feed gives them all of that in a balanced ratio that you can apply weekly. We have grown tomatoes commercially with these.

Our team’s top picks

What to look for in a liquid fertilizer for tomatoes

• NPK ratio: aim for 3-4-6 to 5-6-10 (more potassium than nitrogen).
• Look for added calcium and magnesium — most tomato problems trace to those two.
• Seaweed-based liquid feeds add micronutrients and stress tolerance.
• Concentrated liquids are far cheaper per litre than ready-mixed.
• Apply weekly during fruiting; halve the rate if you also use slow-release granules.

Frequently asked questions

How often should I feed tomatoes?

Weekly during fruit set, fortnightly during foliage growth. If you also use slow-release granules at planting, halve the liquid feed rate.

Why are my tomatoes getting blossom end rot?

Almost always uneven watering, not calcium deficiency. The soil has plenty of calcium; the plant can't move it without consistent moisture. Mulch heavily and water deeply at the same time each day.

Organic or synthetic fertiliser?

Organic feeds the soil microbes that feed the plant — slower but builds long-term fertility. Synthetic feeds the plant directly — faster results but no soil benefit. We use organic in our soil and a small synthetic boost in containers.

Can I over-fertilise tomatoes?

Yes — and it costs you fruit. Too much nitrogen produces lush foliage but few flowers and tomatoes. If your plants are growing fast and dark green with no fruit, ease back on nitrogen.

Bottom line

If you only take one thing from this guide, it is that quality matters more than spec on paper. The picks above have been chosen because our team uses them or trusts them — not because they are the most expensive or have the flashiest marketing. Buy once, garden often.