Lilies come out of the pond for spring cleaning

THE fat, spreading tubers of hardy water lilies -- the most commonly kind planted in pots sitting in a pond or pool -- need to be shortened and repotted if they are to keep blooming. It’s as inevitable as taxes, and done right around the same time. You might want to make a note on your calendar, next to that appointment with the tax guy, to repot lilies by early April, just as they are coming back to life.

Repotting is a wet and messy job but it must be done or the ravenous tubers will grow right out of their container and start wandering around the pond bottom searching for new soil and more nutrients. Containers for hardy lilies must be at least a foot wide to accommodate a year’s worth of growth but they need be only 6 to 8 inches deep.

Bill Dimino of Acquabella Water Features (www.acquabellawaterfeatures.com) in Los Angeles says he uses the shallow, foot-wide, black plastic nursery containers found at some home centers because they are tough and virtually invisible underwater. The less common tropical water lilies do not have tubers so they need repotting less often.

All aquatic plants grow best in clay garden topsoil with no amendments. Never use potting soils because they, or any amendments for that matter, will float to the pond’s surface. The plants are accustomed to growing in thick mucky soil such as is found on the bottom of a natural pond. In fact, the topsoil in the containers will turn into a black muck after a year underwater and it can really stain paving and clothes, as well as fingers, so have the hose nearby to wash things off. Dimino sometimes adds gravel to the bottom of the container to weigh it down and a little gravel on top so fish (koi in particular) won’t disturb the soil.

Never let the plants dry, and get them back into the pond as quickly as possible. A 12-inch-wide container full of soaking wet soil is surprisingly heavy so rather than lifting the container out of the pond, consider sliding it up a sturdy 2-by-10-inch lumber ramp. Once the container is out of the water, here’s what you need to do:

Step 1: Remove all but the youngest curled leaves. Cut though the tuber with an old serrated kitchen knife, leaving about 5 inches of the growing tip. Tilt the container on its side and carefully slide the entire root mass out, taking several inches of soil from the bottom and being careful not to damage any of the new growth. Cut the root ball down to about 6 to 8 inches at its widest. Discard the rest of the root ball and old tuber.

Step 2: Cover the drainage holes (if any) with strips of newspaper so the new soil won’t leak out. Put a 2-inch layer of new garden soil in the bottom and then sprinkle a little bloom-type fertilizer that is high in phosphorus on top (or use special pond fertilizer tablets). Cover the fertilizer with a little more soil.

Step 3: Put the tuber and root ball back in the container, against one side of the pot with the growing tip facing away from the side so it will have plenty of room to spread. The plant should sit on top of the new soil. Unlike other potted plants, the soil and the top of the root ball can be flush with the top of the container.

Step 4: Fill with soil, so the growing tip barely protrudes. Some people top the soil with sand or gravel to keep the water from getting cloudy. Water to settle the soil and put the container in the pond before the leaves dry out. It will bubble as the trapped air escapes. In small ponds, it will take a day or more for the water to clear.