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How to plant water lilies: depth, pot, fertilizer and winter

How to plant water lilies: depth, pot, fertilizer and winter

Plant a water lily in a wide pot, at least 14 inches across and holding about a cubic foot of heavy clay or clay loam garden soil (never bagged potting mix), with the crown left uncovered and gravel over the rest of the soil. Set it in with a few inches of water over the crown, and lower it as the pads reach the surface until the crown sits somewhere between 8 and 18 inches down. Push fertilizer tablets into the soil once a month from May to September for a hardy lily, or every two weeks for a tropical one, and give it at least six hours of direct sun. Hardy lilies spend the winter in the deepest part of the pond. Tropicals go in only when the water reaches 65 to 70°F and come out before frost.

What the extension sources say

The Missouri Botanical Garden's fact sheet sets out the two groups. A hardy lily's rootstock "will survive as long as the water does not freeze solid," while tropicals "will die if left to overwinter in USDA Hardiness Zones 1 to 9" and can be told apart by "the serrated or toothed margin of their leaves." The University of Missouri's David Trinklein, writing for MU Extension in 2017, says tropicals should wait until the water is "quite warm (65° F, or above)." The Garden asks for air and water "at least 70°F."

On pots and soil the sources agree. Trinklein writes that "a container that holds about one cubic feet of soil is ideal" for standard varieties (a cubic foot is about 7.5 gallons), that dwarfs need "9 to 10 inches in diameter," and that lilies "grow well in fairly heavy clay soils low in organic matter." The Garden wants containers "wider than they are tall," filled with "clay loam garden soil," and warns that "Soilless mediums such as peat moss, bark, or those containing perlite are not recommended because the material will float." Utah State's Jerry Goodspeed (2003) says to avoid "potting soil mix or a light soil." The only dissent is the University of Florida's Gardening Solutions page, which says "new potting soil" and gives no reason.

On feeding, the Garden says "Hardy water lilies should be fed once a month, while tropical water lilies are typically fed once every two weeks," from May to September. Tropical feeding "should cease toward the end of September." Trinklein puts tabs in at planting and "later, according to label directions." One label, API's Aquatic Plant Food Tablets, reads "Use one tablet for every gallon (3.8 L) of soil," monthly "until the water temperature reaches 70 degrees Fahrenheit," then twice a month, starting at 50°F in spring and stopping when the water drops below 60°F in fall.

Water over a lily, by authoritative source. Each measures from the point it names.
SourceDepthMeasured from
Missouri Botanical GardenAt least 6 inches, 8 to 10 inches preferredThe crown
MU Extension10 to 12 inches, dwarfs 5 inchesThe crown
Texas A&M AgriLife6 to 18 inchesThe plant ("covered with")
Utah State ExtensionHardy 18 to 24 inches, tropical 6 to 10 inchesNot stated
NC State Extension3 inches to 2 feet, by plant sizeWater depth

For sun, the Garden says "at least 6-8 hours of direct sunlight," with some cultivars tolerating 4 to 6 hours, and Trinklein gives "a minimum of six hours." For spread, NC State's plant toolbox lists the genus at 2 to 12 feet wide, and UF's fact sheet on the hardy 'Attraction' says it "needs about 4 feet to spread its leaves." Texas A&M says to "cover 50 to 75 percent of the surface area of the pond, or approximately one for every 10 square feet." Trinklein says to thin until "about 40 percent of the water's surface" is open. For dividing, he says crowding takes "four or five years" to set in. For winter, he leaves hardy lilies in "if the water does not freeze solid. In Missouri, pools should be at least 24 inches in depth." The Garden stores tropical tubers in "damp sand" in the dark "around 50-55°F."

What contractors and growers do

The Pond Guy's planting guide calls for "a five-gallon pot for one water lily," "between three and six inches of water above the growing tip" at first, and "one or two fertilizer tablets" every two to four weeks. It divides "every two or three years" into pieces "three to four inches long," and after the first frost it cuts the foliage and moves the pot to the deepest part of the pond. Its tropical page keeps tubers in damp peat, sphagnum or sand in a room "warmer than 50° F" until the water is back to 60°F.

Aquascape's planting page refused our fetch. Its search snippet calls for a pot "at least 14″ in diameter," tabs pressed in "around the edges," river rock on top to deter "curious koi," and depth as "shown on the waterlily's plant tag." Mike Hermann of Colorado Pond Pros in Longmont, an Aquascape-certified contractor, uses pots "14 to 16 wide inches," "loam garden soil - not regular potting soil!", starts a rhizome "at about 6 inches depth" and lowers it "to 12 to 24 inches," adds tabs "every 4 to 6 weeks," and divides "Every 2 or 3 years," in the fall. Florida Aquatic Nurseries uses "3 to 5 gallon" pots, "2 to 4 fertilizer tablets," lowers hardies from 6 inches to "12 to 18 inches or deeper," and asks for "8 to 10 hours of direct sunlight."

In TEAM Aquascape's 5 Tips for Water Lilies, Brian tells a tropical from a hardy by the leaf edge, as the Garden does, and puts a lily in 18 inches to three or four feet of water. He does not step it down. Nursery lilies are grown in 10 inches to a foot of water, he says, so the pads start out submerged: "give that Lily 24 hours." He covers the soil with gravel because koi root in it, keeps the lily out of the current running to the skimmer, and warns that "I've seen tropical water lilies get 15 feet in diameter." On a Garden Pond Forum thread, Lisak1 used Aquascape tablets, Highland Rim tablets and tomato spikes, with the "same results with all three."

Where the tiers differ

The depth numbers look further apart than they are because each source measures from a different place: the growing tip, the crown, the top of the pot, or the pond floor. A pot standing on a shelf puts the crown a pot's height above the shelf. Measure from the crown, and the 3 to 6 inch start and the 8 to 18 inch finish describe one lily as it grows. Brian's 18 inches to four feet is water depth for a big lily in a koi pond.

Texas A&M's one lily per 10 square feet is a planting rate. A mature lily with UF's 4 foot spread covers about 12.6 square feet, and tropicals grow far larger, so at that rate the pads soon overlap and Trinklein's thinning begins.

Lilies for a given surface: Texas A&M's planting rate, and mature lilies with a 4 foot spread (about 12.6 square feet each) covering 50 to 75 percent
Surface areaOne per 10 square feetMature 4 foot lilies for 50 to 75 percent
100 square feet104 to 6
200 square feet208 to 12
400 square feet4016 to 24

A 3,000 gallon pond with a 2 foot average depth has about 200 square feet of surface. Lilies need the deeper water, so most ponds take fewer than the table says, with marginals filling the rest. Our guide to how many plants a pond needs covers that split.

Feeding intervals run from two weeks to six. The Garden sets the interval by type and the API label by water temperature, so follow the label on the tab you buy. Dividing runs from every two or three years (The Pond Guy, Colorado Pond Pros) to every four or five (MU Extension), so divide when the blooms fall off or the roots crowd the pot.

What to do

  1. Pick hardy or tropical. Serrated leaf edges mean tropical, which in zones 1 to 9 has to come inside for winter.
  2. Measure the deep zone's surface and decide how many lilies it holds at a spread of 4 feet or more each, with one lily per pot.
  3. Use a pot wider than it is tall, at least 14 inches across, and fill it about two-thirds with wet clay loam garden soil. Lay a hardy rhizome at the edge with its crown pointing toward the center and left uncovered. Push the tablets in near the pot wall, away from the crown, then cap the soil with gravel.
  4. Place it in still water, away from waterfall spray and from the current running to the skimmer.
  5. Start it on blocks with 3 to 6 inches over the crown, and lower it as the pads reach the surface until the crown sits 8 to 18 inches down. Wait for 65 to 70°F water before putting in a tropical.
  6. Feed hardies monthly and tropicals every two weeks from May to September, at the label's rate, and stop at the end of September.
  7. Pull yellow pads, and thin so about 40 percent of the surface stays open.
  8. In fall, cut back hardies and set them in the deepest water, which has to stay unfrozen at the bottom. Store tropical tubers in damp sand in the dark at 50 to 55°F. Our winterizing guide covers the rest of the pond.

Do not use potting mix or anything with peat, bark or perlite, because it floats out of the pot.

The PondTools surface-area calculator

The PondTools surface-area calculator (also standalone) takes a surface area in square feet, or pulls it from a pond you traced in the PondTools app, along with water temperature, the coldest night and the kind of fish. For lilies, take the traced area of the deep zone, multiply by 0.5 to 0.75 for the coverage you want, and divide by about 12.6 square feet for each 4 foot lily.

Sources