How many plants fit in a window box?

A 60 cm window box typically fits 5-6 bedding plants. Use trailing plants at the front and upright plants at the back for the best display.

What depth should a window box be?

Minimum 15 cm for bedding plants. 20 cm or more for herbs and larger plants. Deeper boxes retain moisture better.

How often should I water window boxes?

In summer, daily or even twice daily in hot weather. South-facing boxes dry out fastest. Add water-retaining gel to the compost.

What plants work best in window boxes?

Trailing petunias, lobelia, geraniums, fuchsia, herbs, and small bulbs. Choose plants suited to your aspect (sun or shade).

How do I stop window boxes drying out?

Use compost with water-retaining gel, add saucers if possible, and water morning and evening in hot weather. Self-watering window boxes are excellent for hot positions.

GardenCalcs

Window Box Calculator — Compost & Plant Quantities

Calculate compost volume and plant quantities for window boxes.

Box Length

Box Width

Box Depth

Plant Type

How We Calculate This

Volume = Length × Width × Depth (in cm), divided by 1000 for litres, with 15% reduction for drainage material.

Plants = Floor(Box Length ÷ Spacing) + 1, using recommended spacing per plant type.

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates based on standard gardening guidelines. Results may vary with soil conditions, climate, and plant varieties.