Do pots really need a drainage layer?

Opinions are divided. Modern thinking says drainage layers can create a perched water table. The most important thing is having drainage holes. A thin layer of crocks stops compost washing out.

How deep should a drainage layer be?

Keep it thin — 2-3 cm for most pots. Deeper drainage layers waste root space and can actually hold water.

What materials work for drainage?

Broken crocks, clean gravel, perlite, or LECA (clay pebbles). Avoid polystyrene as it can float and break up.

Lightweight Expanded Clay Aggregate. Clay balls that are lightweight and retain some moisture. Good for large pots where weight is a concern.

Do pots really need drainage holes?

Yes, drainage holes are essential. Without them, water collects at the bottom and roots rot. If using decorative pots without holes, use an inner pot with drainage.

GardenCalcs

Drainage Layer Calculator — Pot Drainage Material

Work out crocks or gravel needed for container drainage layers.

Pot Diameter

Layer Depth

Material

Number of Pots

How We Calculate This

Volume per pot = π × (Diameter/2)² × Layer Depth (in cm), converted to litres.

Total = Volume per pot × Number of pots. Weight uses material density: gravel 1.5 kg/L, crocks 0.8, perlite 0.1, LECA 0.4.

Frequently Asked Questions

Related Calculators

Pot Volume Calculator

Calculate the volume of round, square, or tapered plant pots.

Container Compost Calculator

Work out how much compost you need to fill your containers.

Window Box Calculator

Calculate compost volume and plant quantities for window boxes.

Hanging Basket Calculator

Work out compost, liner, and plant quantities for hanging baskets.

Grow Bag Calculator

Calculate how many grow bags you need and plants per bag.

Last updated: February 2026

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