Propagating water lilies is an easily learned pond gardening skill. It depends mostly on timing and the use of a knife.
When To Divide
You know it is time to divide your water lily when the flower production slows down, the blossoms are hidden among the leaves and sometimes the leaves themselves tend to rise slightly above the water level. These are signs the roots are getting too crowded.
This is fairly simple.
Dig the plant *before* it begins to grow in the spring.
Do not divide the plant in the fall at all as it really needs the time to prepare for winter.
Summer division can be done but it really isn’t recommended.
Commercial growers wade into their ponds as soon as the ice is off the pond (yes, it is really cold and no- this is not their favourite job).
I note a water nursery favorite job is to do pond wading work in the heat of the summer.
You Have the Lily Out of the Pond Now.
Once you have the lily out of the pot or out of the ground, wash off all the roots with a strong jet of water.
You can’t hurt this root with a hose so be firm in getting rid of all the dead or decaying root matter and soil. (In a mature lily, there will be dead and decaying old roots surrounding the plant and this is natural.
Clean off the root, cut off any dead or decaying material so you wind up with strong, healthy thick root sections.
Cutting The Root
The second phase in propagating water lilies is to use a knife and simply cut off 4-5 inch chunks of the root.
You’ll see developing “eyes” or pointed-shoots off of the main root. Cut a 4-5 inch section so it includes at least one eye and replant it as normal (slightly angled downward with the bud eye above the soil line and the rooted end below the soil).
Discard any section of the old main root without eyes, it will not grow but will rot away.
How Big To Cut
The size of this cutting is variable.
In nursery work, the bigger the division, the faster the plant will bloom again. Small shoots – the size of your thumb – will grow but they will not flower for several years until they bulk up to the size of two to three thumbs across and two thumbs (4-5 inches) long.
I’ve seen roots that are almost 3-4 inches across be divided and these will flower the first year after division (if they have an eye).
I also note that some varieties tend to produce larger roots than others so the width is not an indication of plant health.
Do not worry about dressing the wound or anything like this.
Replant all divided sections as soon as possible and do not let the root dry out. It is normal to plant the roots so the growing tip is in the center of the pot and the blunt cut end is facing or close to the side of the pot.
These are the two things you really need to know about propagating water lilies.
Do it early and do it with a sharp knife.
You can find other articles about backyard ponds here.
Other plant propagation techniques are here