Gardening glossary
Foliar feeding
Foliar feeding takes advantage of the fact that plant leaves can absorb small amounts of dissolved nutrients directly. Spray a finely-misted, very dilute liquid feed onto the underside of the leaves where most of the stomata are, and within hours some of the nutrients are inside the plant.
Where foliar feeding genuinely helps:
- **Quick fixes for micronutrient deficiencies.** Iron-chelate, magnesium sulphate (Epsom salts), and chelated manganese applied as a foliar spray correct chlorosis faster than soil applications, especially when soil pH is locking the nutrient up. - **Container plants where soil is depleted** between repotting events. - **Mid-season top-ups** during peak fruiting for tomatoes, peppers, cucumbers, and squash. - **Recovery from transplant shock** with a kelp or seaweed-based foliar feed.
Where it does *not* do much:
- **Macronutrient bulk feeding.** Leaves cannot absorb enough nitrogen, phosphorus, or potassium through their surfaces to replace a soil application. Foliar feeding is a top-up, not a bulk feed. - **Replacing soil health.** No amount of leaf spray substitutes for compost, mulch, and a healthy soil food web. - **Crops with hairy or waxy leaves** that resist spray adherence (some brassicas, alliums) — much of the spray runs off without absorbing.
How to foliar-feed safely:
1. **Dilute heavily.** Use roughly half the label's soil-application strength — undiluted foliar sprays can burn leaves. For seaweed extract, 5 ml per litre of water is a typical safe rate. 2. **Spray in cool morning or evening light.** Hot midday sun amplifies any leaf burn risk and stomata close, reducing absorption. 3. **Spray the underside of leaves** preferentially — stomatal density is far higher there. 4. **Use a fine mist** that wets the leaves thoroughly but does not run off in big droplets. 5. **Avoid foliar feeding flowering crops in mid-bloom** — sprays can damage delicate petals and disrupt pollinators. 6. **Add a wetting agent** (a tiny drop of mild dish soap, 0.5 ml per litre) for waxy-leaved plants — but never with insecticidal soap concentrations.
A reasonable rhythm for vegetable gardens: a fortnightly half-strength seaweed foliar spray from the moment plants start fruiting until harvest. Combined with a balanced soil-based feeding programme, this catches most micronutrient gaps before they show up as visible deficiency.