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Waterlily Soils, Fertilizers, and Pots

by Rich Sacher, New Orleans, Louisiana
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It does not matter if we are hobbyists or commercial growers; we all want to know what is the perfect soil, pot and fertilizer for achieving the best results in growing waterlilies. The question is simple, but not the answers. We need explanations here. Once we understand the underlying principles involved, I am confident that anyone can successfully grow beautiful waterlilies in almost any soil, with nearly any fertilizer, and in almost any kind of container. 

The Perfect Soil

Nymphaea 'Starlight'
beautifully grown in "spillway sand",
a pot with holes,
and top-dressed with
granular fertilizer.

Many books and articles on growing waterlilies state that clay soil works best for the purpose, but that is rather vague. What does "clay" soil mean? Is it 20% clay? 50% clay? If your local soil is not much more than beach sand, what are you supposed to do? And what is so special about "clay" soil, anyway?

The recommendation for using soil that contains clay comes from the fact that clay particles serve as a colloidal sponge, adsorbing and holding onto dissolved nutrients until the lily roots access them. In extremely sandy soil, added nutrients quickly dissolve and migrate out of the sand into the water. There they only feed algae, not the waterlily. Clay in soil helps to slow the loss of fertilizer to the water, keeping it in the soil pot where the roots access it. 

Older books on water gardening often give a formula for waterlily planting that includes bone meal, composted sod, horse manure and some topsoil. This combination provides for slow release of nutrients from the bone meal and manure, with sod serving as the organic sponge that holds onto the nutrients a while so they do not migrate too quickly out of the soil.

Since most of us do not live on farms with available sod and horse manure, we obviously need other options for waterlily soils and fertilizers. These days, we have lots to choose from!

When I was a teenager, I grew waterlilies successfully in pure masonry sand . . . sand so devoid of any clay or organic matter that it had no nutrients of its own. In fact, workers mixed this same sand with cement to pour a concrete walkway; after forty-five years, that walkway is still in fine shape! I knew that this "soil" needed lots of fertilizer on a regular basis. So I used a teaspoon (5 milliliters) of granular fertilizer and inserted it into holes in the sand that I made with a stick. I did this every two weeks during the growing season, and it produced great results. At the time, no one sold fertilizer tablets for water gardening . . . or, if they did, I was not aware of them. So, yes, you can grow waterlilies in pure sand as long as you maintain fertility.

Today I use what we locally call spillway sand, which the Mississippi River deposits as it passes through the Bonnet Carre spillway, a flood control project west of New Orleans. Although very sandy, it does have some fine silt and clay in it, perhaps 10%.  

To pot up lilies for the nursery, I put a handful of peat moss in a ten-inch (24-cm) diameter pot (to provide organic matter). Next, I add a handful (0.25 cup [0.6 liter]) of cheap, very coarse chemical fertilizer (this year, 14-14-14). After that, I fill the pot with spillway sand and mix everything thoroughly. Then I plant the lilies, either transplanting them from smaller pots, or planting them as bare root plants. Because my soil is so sandy, (the peat moss helps, but is not a perfect solution), beginning three weeks later, I apply a supplemental fertilizer tablet every two weeks during the growing season.  

If you have soil with some clay in it, omit the peat moss (or not), and use the same amount of coarse fertilizer as above. Then perhaps fertilize your ten-inch (24-cm) potted hardy waterlilies with one tablet every three weeks (instead of every two weeks) during the growing season. Because tropical waterlilies grow at such a rapid rate once the temperatures are warm, I give them slightly more fertilizer than hardies.

Any soil you dig from your property is probably just fine for waterlilies, as long as it does not include lots of bark, mulch, leaves, pesticides, or floating materials. After all, the fertility of your local soil is not an issue when you add granular fertilizer at planting time, and then add fertilizer tablets at regular intervals.

Ironically, your own soil may be quite superior to so-called "topsoil" sold prepackaged in bags at nurseries. These soils often have finely chopped bark and peat moss mixed through them, making them great for flower beds and potted plants, but unsuitable for waterlilies. Sometimes "topsoil" mixes contain so much buoyant organic matter that the soil floats out of the submerged pot. Additionally, the pH may be too low; or the soil structure may be too loose to hold the waterlily in place.

I certainly do not want to minimize the value of soils that have some clay or organic matter in them. They do help to regulate the rate at which added fertilizers dissolve and migrate into the pond water. However, such ideal soils are not necessary for spectacular results. No single, magic, ideal soil exists that is required to grow beautiful waterlilies. For most people, whatever soil they dig up from their property can become quite suitable for growing waterlilies.

However, if your native soil is so full of clay that you can spread it with a butter knife when it is wet, and you can throw a pot or make sun dried bricks out of it, you should probably mix your clay soil with sand (half and half works) before using it for lilies. Otherwise, the soil may be too dense for the roots and oxygen to penetrate it effectively.

The bottom line on soil for waterlilies: use mostly sand or good topsoil containing some clay, but keep it free of floating materials. It must be heavy enough to sink quickly when wet, and not float out of the pot. It does not need to be especially fertile. In fact, it need not be soil at all! It could be masonry sand, or a ceramic-based cat litter. The main requirements are that it be heavy and firm enough to hold a newly planted waterlily in place. If it can hold onto dissolving fertilizer, too, so much the better. 

The Best Fertilizer

When you grow waterlilies in pots, they depend on whatever nutrients exist within their planting container. The pot confines all their roots. I mix granular fertilizer into the soil when planting or transplanting a waterlily. As mentioned before, I use a cheap, coarse, general-purpose fertilizer packaged in 40-pound (18 kilo-) bags. Sometimes I use 8-8-8; last year I used 13-13-13; this year, it happens to be 14-14-14. Once, I could find only 10-6-4. All of them work just fine. The overall texture of this cheap fertilizer is coarse, but I detect some fine fertilizer dust, too. Fine dust makes for a quick release of nutrients, while the coarse particles take many weeks to dissolve completely.

Although we can make an educated guess as to what fertilizer formulation works best for waterlilies, I really do not know what the perfect fertilizer might be. I do not think anyone else does, either!

The numbers given on a bag of fertilizer refer to the percentage of nitrogen, phosphorous and potassium in the mix. Since nitrogen promotes leaf growth, you might think that 10-6-4 would make many waterlily leaves, and few flowers. That certainly could be the case with some terrestrial plants. For terrestrial plants where we want to encourage blooming, we prefer a fertilizer with low nitrogen, high phosphorus and low potassium, like 5-20-5.

However, that rule does not seem to apply to waterlilies. This is good news, since you may use whatever fertilizer you have on hand. Except for completely water-soluble fertilizers, which dissolve and migrate into the pond water too quickly, almost any granular fertilizer may be all right for mixing with your soil. I do not have experience with pelleted, slow release fertilizers like Osmocote. Since they depend on moisture to release their nutrients, I cannot recommend them for mixing with waterlily soil. I suspect they release their nutrients more quickly in water (and not last as long as expected) than they do in soil when they are applied to terrestrial plants. Nevertheless, you know what? If that were all I had at hand, and I needed to transplant some lilies right away, I would use it!  

  We have discussed mixing fertilizer into the soil prior to planting the waterlily. Now we need to think about supplemental feeding after the plant has been growing for a few weeks. The warmer your climate, and the longer your growing season, the longer you need to feed your lilies. I use tablets with a 10-26-10 formulation. I put one tablet every two weeks in a ten-inch (24-cm) pot. For a sixteen-inch (41 cm) pot, I use three tablets every two weeks. The bigger the pot, the more tablets I use. A Victoria in a two-foot (0.6- meter) by three-foot (0.9-meter) tub may require fifteen tablets every two weeks! 

Since many roots gather around the outer edges of a pot, I like to push tablets into the soil about an inch (2.5 cm) or so from the edge of the pot; this avoids breaking the roots. I push the tablet in to a depth of about two inches (5 cm), and then pinch the hole closed. If the plant has become very root bound, consider using a dowel to make a hole in the soil, and then insert the tablet.

Okay, let's say you live in a small town and no one stocks fertilizer tablets. What do you do? If you must transplant and fertilize immediately, and cannot wait for a mail order shipment of tablets, you could lift the lily out of the water, make a hole in the soil, and pour a teaspoon (5 milliliters) of granular fertilizer into the hole. Pinch the hole closed. Fish LOVE to dig up fertilizer. Pinching the hole closed, or putting a rock over it, prevents them from feasting on this treat. And no, it does not hurt them if they eat some of it.

As I mentioned, many years ago it was customary to put granular fertilizer into a roll of cloth or paper and insert it into the soil. There it slowly dissolved and fed the lily. In the days before waterlily fertilizer tablets were available, I used tree spike fertilizer for supplemental feedings. I hit the six-inch (15-cm) spike with a hammer, broke it into four pieces, and pushed a piece into the soil. This way I made my own tablets that worked just fine. Still do.

Not all fertilizer spikes are equal, however. Obviously, a tiny fertilizer spike meant for African violets is not big enough or potent enough to have significant effect on your waterlily. The amount of fertilizer used for each supplemental feeding in a ten-inch (24-cm) pot should be about a teaspoon (5 milliliters) to a full tablespoon (15 milliliters) if measured in granular form.

So, what is the underlying fertilizing principle here? It is this: Never let your lily run out of nutrients. Feed it whatever you have rather than let it go hungry. Once a waterlily shows signs of starvation, it could take two or three weeks to reverse the process with a new application of fertilizer. Meanwhile, it may cease blooming. Better to maintain high levels of steady fertilizing so the lily grows constantly, rather than wait until a drop in flower production or yellowing leaves finally remind you that you have fallen down on the job! 

Victoria top-dressed with 14-14-14

Fertilizer Top-Dressing

Top-dressing refers to applying fertilizer to the soil surface rather than mixing it into the soil. We can fertilize a crop of corn or tomatoes by sprinkling fertilizer between the rows. Then we water the soil to begin the process of releasing the nutrients. We place the fertilizer a few inches (1 inch = 2.54 cm) from the plant stems so we do not burn them with fertilizer.

I do not know if I am the only one who does this with waterlilies, and there are some precautions to take. Nevertheless, you may find this same practice useful for fertilizing waterlilies in certain situations. 

For example, I once had a Victoria at our zoo. It was not growing as large as it should despite having good soil with plenty of fertilizer in it. However, the leaves were only three feet (0.9 meter) across, and it had remained that way for almost a month. In the trunk of my car, I had some Scott's Turfbuilder, which is very high in nitrogen. (29-3-4). I took two measuring cups (0.5 liter) of Turfbuilder and poured it into the water, right above the crown of the plant. "Grow or die!" I said. I really expected that the Victoria would burn and die from so much fertilizer. Instead, it grew. Wow, did it grow! What a revelation that was.

I am not recommending that we all run out and pour fertilizer on the waterlily crowns. Nevertheless, I find that when I have hundreds of waterlilies that need supplemental feeding, it is much quicker and easier to release granular fertilizer under water, on top of the soil in the pot, while avoiding getting too much in the center of the plant. When plants are too numerous, or the lily is too root bound to easily push tablets into the soil, top-dressing with fertilizer works just fine.

Keep these two cautions in mind. First, if you top-dress a very young plant, you may kill it. Reserve top-dressing for mature plants in very active growth. Second, ample loose fertilizer on the soil means that the water may quickly turn green as algae multiply in response to increased nutrients in the water. 

I dye the water black in display ponds where I top-dress lilies with fertilizer, so I do not worry about green water. In my growing ponds, which are not on display, I do not care if the water turns green. (And neither do the lilies!)

To this day, I top-dress Victorias for supplemental feeding. For each feeding, I use whatever coarse fertilizer I have at hand, and use about a cupful for a pot that is two feet (0.6 meter) by three feet (0.9 meter) and eight inches (20 cm) deep. I pour the fertilizer in a circle, all around the center of the plant. This saves me all the cuts and punctures that I would otherwise suffer if I attempted to push tablets through a Victoria's minefield of thorns. Otherwise, it always bites the hand that feeds it! 

Black dye
for display ponds

Another candidate for topdressing is tropical lilies that have overgrown their pots late in the season. They may be too large or too heavy to repot into something bigger, but top feeding with granular fertilizer keeps them growing strongly, even when badly pot bound. On occasion, I add an inch (2.5 cm) or two (5 cm) of fresh soil on top of the roots after fertilizing, to supply more room for new root development. This method saves a lot of labor, and nicely sustains a pot-bound tropical waterlily to the end of the growing season.

One problem that may arise late in the season is that a lily becomes large and buoyant enough to float off the pond bottom, even though it remains well rooted in its pot. In this case, I tie a short piece of rope between two concrete blocks, place the blocks on each side of the lily pot, and let go. The weight of the blocks holds any floater in place on the pond bottom for the rest of the season! 

The Ideal Pots

The ideal waterlily pot should be two or three times as wide as it is deep. Waterlilies prefer to send their roots out horizontally, rather than vertically. Having said that, we still sell all our lilies in pots that are ten inches (24 cm) in diameter and eight inches (20 cm) deep. The weight of the potted lily is a consideration, since customers should be able to handle them without undue strain. This size pot is large enough to keep the lily growing throughout our seven-month season, assuming you feed it every two weeks. However, I believe the lily would be happier in the same amount of soil if the pot were six inches (15 cm) deep and 14-16 inches (36-41 cm) in diameter. 

Most plastic pots sold in the industry for waterlilies are deficient because they:

1. are too narrow and too deep
2. have no holes in the sides near the bottom

Perforate the sides of your pots near the bottom allows for water circulation. More importantly, this enables oxygen circulation at the bottom of the pot. Pots with slits or small holes near the bottom allow lily roots to grow right to the pot bottom, and remain healthy all season long. Without these holes, the roots that first reach the pot bottom eventually die and rot, creating a three- or four-inch (8- or 10-cm) layer of useless soil. This is because of the anaerobic (no oxygen) conditions in the soil at the pot bottom cause this uselessness. The dead zone slows or stunts the lily's growth. You can prevent this by making five to six slits in the sides of the pot, near the bottom. Unfortunately, our industry produces waterlily pots with no holes in them; maybe everyone is afraid some soil might drift out and dirty our ponds. The pots do not need round holes; small slits do the job.

I use a large knife to make stab holes in every lily pot before using it. The improved performance by the lilies is easy to see. Even in pots measuring 16 inches (41 cm) in diameter and seven inches (18 cm) deep (close to my "ideal" ratio for diameter and depth), I slice holes in the sides of the pot near the bottom. Interestingly, I never see any soil coming out of these holes. They are one-inch (2.5 cm) long, narrow slits; they allow water circulation into the root system without allowing soil to ooze out into the pond.  

Remember, with perforated sides on waterlily pots, you will grow happier lilies. They will use all the soil in the pot instead of confining their roots to the better-aerated top six inches (15 cm) of soil. Perhaps the industry will eventually catch up with us, and produce pre-perforated lily pots. You can always find uses for pots with no holes, however. For instance, lotus and bog plants grow happily above ground in pots without holes rather than submerged in the pond. Nevertheless, for waterlilies, the recommended holes make a big difference in improved performance.

I hope that these observations, gained from many years of splashing around in lily ponds, will help you to become even more successful and satisfied while growing these gems of the pond, the lovely waterlilies. 

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