Pond Plant Calculator | Find How Many Pond Plants You Need

How the 3-2-1 Rule works

A healthy pond relies on plants to do much of the work: using up the nutrients that feed algae, shading the water, adding oxygen and giving fish and frogs somewhere to shelter. The We Know Water Gardens 3-2-1 Rule makes it simple to get the balance right. For every square metre of pond surface, we recommend:

• 3 oxygenating plants: submerged plants that release oxygen into the water and compete with algae for nutrients. They are the hardest-working plants in a clear pond.
• 2 marginal plants: plants that grow in the shallow edges, adding height and structure, filtering water through their roots and giving frogs a way in and out of the pond.
• 1 flowering pond plant: usually a water lily, whose floating leaves shade the water, keep it cooler and give fish cover from birds.

Worked example

A pond 2 metres long and 1.5 metres wide has a surface area of 3 m² (2 × 1.5). Using the 3-2-1 Rule, it needs:

• 9 oxygenating plants (3 × 3)
• 6 marginal plants (2 × 3)
• 3 flowering pond plants (1 × 3)

That is 18 plants in total. The calculator above does this sum for you.

Measuring round or irregular ponds

The calculator multiplies length by width, which is exact for a rectangle. For other shapes:

• Round ponds: enter the diameter as both length and width, then reduce the plant numbers by about a fifth, since a circle covers roughly 80% of the square around it.
• Kidney or freeform ponds: measure the longest length and the average width. If in doubt, round up slightly; a few extra plants are better than too few.
• Container and patio ponds: for a half barrel or water bowl, one or two oxygenators, one marginal and one small water lily or floating plant is usually plenty.

Tips for a balanced pond

• Aim to cover about half to two-thirds of the surface with leaves once plants are established. This shades out algae without leaving too little open water.
• No filter? Lean towards more oxygenators and filtering pond plants, which help keep the water clean naturally.
• Want frogs? Add extra marginals and rushes around the edges to give them shelter and an easy way in and out. See our frog habitat plants.
• Plant in the warmer months. Spring and summer give pond plants the best start in most of Australia.
• Not sure where to begin? Our pond plant starter packs combine the right mix of plants in one order.

Frequently asked questions

Can I have too many pond plants?

Yes. If plants cover the entire surface, the water below can lose oxygen and fish have less room to swim. The 3-2-1 Rule is designed to stay on the safe side, and plants can be thinned out as they grow.

Do I still need oxygenating plants if I have a filter?

We recommend them in almost every pond. A filter cleans the water, but oxygenators use up the nutrients that algae feed on, so the two work best together.

What if my pond is very deep or very shallow?

Depth changes which plants suit your pond more than how many you need. Marginals need shallow shelves, while water lilies prefer deeper water. If you are unsure, ask us for free pond advice and we will help you choose.