If lilies arrive in solid pots they should be repotted into an appropriate sized aquatic basket before placing in your pond. See Planting Water lilies for general size guidance or details on the web page of the lily. If the lily arrives already potted in aquatic basket then it will be fine to drop straight into your pond and should be good for at least another season before you need to worry about increasing the basket size. However if the lily is very well established in its basket when it arrives, with strong root growth coming through the mesh, then it may benefit from being potted up straight away.
When repotting or potting-up lilies it’s always a good idea to give them a feed with a good quality slow release fertiliser such as Osmocote Exact 5-6. Any lily supplied by us in an aquatic basket will already have had a feed tablet added so will not need anything in its first year, however if you repot into a larger basket you will need to add additional tablets per the instructions.
Remove the lily carefully from its pot or basket by gently squeezing it a few times to loosen it and then turn it upside down, holding the pot/basket in one hand whilst using the other to support the plant, being careful not to damage any foliage or bud. Gently shake the pot back and forth until the lily is released from the container. Protect the lily from sun and wind during potting to prevent it from drying out.
For lilies with a rhizome of the pineapple-type (mainly the native alba), plant the rhizome in the middle of the basket making sure the growing tip is just above the surface of the soil. Most other rhizome types tend to grow horizontally so plant the rhizome as above but instead of in the middle of the basket position it against the side of the basket with the growing tip pointing into the centre and angled up at no more than 45 degrees with the tip just above the soil.
Remove as much of the old soil as possible from the root ball, being careful not to damage the roots. Fill your basket with enough soil to support the base of the rhizome and roots when held at the correct height -this is with the growing tip just level with the top of the basket. Dampen and firm down the soil, tapping the basket a few times on a level surface to ensure there are no trapped air pockets. Hold the rhizome in position in one hand with the roots hanging down into the basket and use the other hand to fill around and under it, pressing the soil into the basket with your fingers to ensure the rhizome is firmly anchored in place. Add more soil to cover the rhizome so only the growing tips are showing just above the soil and there is room to add a 1cm layer of aquatic gravel. Dampen and firm down the soil again, tapping the basket lightly. Now add a layer of aquatic gravel to finish off: this will prevent soil leaching into and dirtying the pond, act as additional weight to anchor the plant and basket, prevent disturbance of the plant from fish and provide an attractive decorative finish.