Lilies can either by planted directly in the bed of a pond or lake if it is a natural pond or has a good deep layer of soil in a lined pond, however planting in an aquatic basket is recommended, as they can be easily moved or lifted for splitting and dividing or just moved to a different area of the pond. If a lily is supplied in a solid pot it should always be repotted into an aquatic basket otherwise it will quickly become too restricted and will run out of nutrients.
Baskets allow nutrients and gases to circulate and the roots can grow through the mesh to support the development of the plant. Over a longer period of time they can even break out of the basket and have been known to ‘move’ around the pond!
The practical maximum sized basket to use would be 10 litres as even these can weigh 15kg or more when wet -the larger 30 litre baskets can weigh 40kg or more so are likely to give you a hernia if you need to lift them for splitting or dividing your lilies! Dwarf varieties are fine in a 2 litre basket, small/medium lilies can go in 5 or 10 litre baskets with the larger varieties best in 10 litre baskets.
The planting medium for the baskets should ideally either be a high quality aquatic soil or a heavy garden loam (i.e. clay based soil) which is both fertiliser and herbicide free. See Repotting Water lilies for potting-up guide.
If you are using a high quality aquatic basket, such as the Finofil ® ones we sell you would not need to line it with hessian, however some lesser quality baskets have a coarser mesh and would need lining otherwise soil will leach out into the water turning it cloudy and also could encourage algae.