Your plants can be divided in the spring and, if in pots that you can lift out of the pond, you could wait till late spring if you so desire as any plant can be divided up to early August. All perennial plants such as all Pickerel, Arrow plants, Iris and any other perennial plant in your pond should be divided approximately every three years depending on how large they have become or how crowded the pot has become.
Marginal plants can be divided two ways; either you can gently pull apart the plants which will leave you with several new plants. Or you will need a knife to cut through the plant. Plants like Pickerel, arrow plants grow in a bulb type and can be easily divided. Gently tease the growing points of the plant apart and/or dividing the plants at a natural breaking point. Iris grow in a rhizone which also can be divided by pulling apart, just be careful that you get some root with each plant. Always throw away mushy or diseased sections. Trim back any old or dying leaves, old rootstock or spent flowers.
If using a knife, clean with a bleach solution before cutting other plants. Some of the bulb plants such as the Arrow plant are late to produce any growth. You will just see the bulb and if it is in a pot, just thin out. If planted in the pond, you may have to look hard for these bulbs or divide later. Iris rhizone can be divided and replanted in the pond. Iris do not need to be planted very deep and only like their rhizone wet. Most of the pickerel, rushes, iris, and arrow plant need to be on the first shelf as they are marginal plants. The second shelf is usually held for the Lilies.
Floating plants (such as parrot’s feather) and oxygenators (anacharis, hornwort) need to be trimmed also. Trim off 6 to 10 inches of the fresh growth at the top of the existing strands. Cut out the middle section of straggly growth. These cuttings will root on their own accord. Parrot’s feather can be tucked into the rock substrate to hold it in place or placed in a pot.
Lilies have two forms:
Clump-Forming Lilies and Tuber-Type Lilies.
Clump Form Lilies
The clump form will produce new baby plants at the base of the mother plant. Wash the soil off the roots and look for these delicate little plantlets at the crown of the larger plant. Gently work them a part. Mix a granular, slow release fertilizer into the soil at the bottom of the plant pocket or pot and replant the largest clump with the crown at or just above the soil surface. Soil just needs to be good clay dirt not potting soil or use aquatic soil (available at any Home Depot). Remove any ragged leaves and flower buds to save energy for root growth. Always use pebbles on top of the soil to prevent fish from disturbing the soil and fouling up the water in your pond. Believe me this can make quite a mess in your pond by turning your water brown if you do not use gravel particularly if you have large fish.!
The tuber form of the water lily produces new plants off the rhizome or tuber. Find a firm piece of tuber with plenty of growth points and use a clean, sharp knife to cut off a section that is at least two inches long (three or four inches is best). It might be tempting to just snap off a chuck, but a clean cut will heal faster.
Mix granular fertilizer into fresh soil at the bottom of the plant pocket or pot and plant the tuber with the cut end against the side of the pot/pocket. Make sure growth points are at or above the soil surface, but the cut end can be below the soil. Layer pea gravel or a couple of well-placed rocks that help keep the plant in place until its new roots anchor it. Also, remove the ragged
leaves and flower buds to save the plant’s energy for root growth.
Tropical Lilies are Different
Starting out as a small, moldy looking bump at the leaf’s sinus (the point where the two lobes of the leaf meet), a tiny plant clone forms. Cut the stem of the parent leaf, turn it upside down on the water surface and a plantlet will grown from the leaf sinus. When roots form, the plantlet can be removed from the parent leaf, planted in a small, soil-filled pot and placed in shallow water.
As with most lilies, when young plants have four or five good-sized leaves, it can be placed in a full size pot or plant pocket and placed in deeper water.
Fertilize again with tablets as the season proceeds. Push tablets down the sides of the pot away from the plant. Continue to feed your lilies about once a month until fall.
So don’t be shy….divide and share with your friends. They are hardy plants and as long as you keep them well hydrated, it is hard to make a mistake besides you will get more bloom from a plant that has more room to grow.