In Central Europe tropical waterlilies are usualy cultivated only in botanical gardens. There they are kept in heated bassins in greenhouses. Often huge Victoria amazonica from Brazil is exposed, for its foliage is very impressive. Its’ leaves become so large and sturdy that they are able to support the weight of a child. Beside Victoria often some blue or purple waterlilies can be found. Those exhibits give the impression that it takes a lot of space and a lot of effort and complexity to grow tropical waterlilies. 

Don’t be fooled by this impression. In the USA tropical waterlilies are to be found everywhere in the country during summer. Their needs are not as high as one might expect. Of course the climatic conditions in the USA are different to those in Central Europe. Due to the typical continenal weather American summers are more stable than our summers with their regular change of rainy and sunny periods. In Central Europe it depends very much on region and weather if tropicals can be kept outside successfully. In vine-growing regions it is always possible, also in some regions in the East with more continental climate. In all other regions you need good luck with the weather or you have to boost a little bit. It is no a problem to keep tropicals in a conservatory or in a greenhouse. A conservatory with a little bassin of brick work containing tropical waterlilies is an absolute showpiece. It takes less space and less money to construct than one might expect. Two to three square meters are enough space. The bassin got to be very shallow (about 40 cms deep) and is best masoned above ground and layed out with a pond liner. If the walls are topped with another layer of bricks above the pond liner they provide very attractive seat with perfect view of the waterlilies. 

When we started to grow tropical waterlilies we kept them in a simple polytunnel for tomatoes. Meanwhile we cultivate them in two big bassins in a large polyhouse. Neither bassins nor polyhouse are heated and yet our waterlilies are in bloom from June till the end of October. Sporadic flowers may appear even later. 

Waterlilies with a difference ... 

Tropical waterlilies do have some characteristics that distinguish them from hardy ones. First of all it is their colour. Only tropical waterlilies show blue and purple in their chart of colours, which makes them so desirable. Moreover their habit is very attractive. While the flowers of hardy waterlilies float on the water surface, tropical ones hold their flowers several centimeters above the surface. It is a noble impression and reminds a bit of lotuses. Tropical waterlilies are also more floriferous than hardies are. There are varieties that produce as many flowers als leaves. The last advantage is that some of them are viviparous. 

Vivipary 

Although the word might sound a bit nasty, the meaning of it is a very nice characateric of some tropicals. Literally ‘viviparous’ means ‘producing living young ones’ (instead of producing eggs or seed). One species of the tropical waterlilies (Nymphaea micrantha)  grows small plantlets on its leaves. When a leaf rots away (what all leaves do after some time) the little plantlet doesn’t rot simply drifts away to find a new home where it can anchor itself and form to a full grown waterlily and later a new colony of waterlilies. Sometimes the plantlets start to bloom when they are still attached to their mother, a quite nice sight! 

This characteristic is dominant and was inherited from Nymphaea micrantha to quite a lot of waterliy hybrid, mainly to blue and purple varieties. To you it means a simple way to propagate your tropical waterlily. All you got to do is planting the baby plant into a pot with loamy soil as soon as it has separated from the nursing leaf. You can also cut the intact leaf and anchor it with the baby plant on top in a pot. The baby plants can be detached from the mother plant at any time of their developement. In very very few cases vivipary appears with hardy waterlilies. In hardy waterlilies the new plant always develope from a spent flower, not from a leaf. 

Daybloomers and Nightbloomers 

Most tropicals bloom during the day, just like hardies do. A few of them however decided to bloom by night. Now why should you want to aquire a plant that blooms during the night? First of all you should take ‘by night’ not too literally. Usually the flowers open in the dawn and close again during the morning of the following day. Second of all you probably have to work during the day. When coming home from work most dayblooming waterlilies – no matter if they are tropical or hardy – will have already closed their flowers. So it is usually only the weekend when you can see those bloom. Some hours later however the night blooming waterlilies start to open  and they will be still open during breakfeast time the following day – weekday lilies with a sense for good timing. Third and last of all it is simply fun to assemble with the whole family and an electric torch at night to go watching the waterlilies bloom. 

How much space needs a tropical waterlily? 

Most tropical waterlilies can adapt their growth to the size of the pot they are kept in. You can grow a tropical waterlily in a bassin with a surface of only one square meter. It looks better if the watersurface has two to three square meters. Tropicals grow in very shallow water, 40 cms are fine but half of it will also do.  

In a conservatory of course you won’t dig a hole to build a bassin. In here the bassin got to rise from the ground. It can be mansoned in brick or timbered in wood, depending on what fits best your conservatory. Inside it is layed with pond liner to make it water-tight. The way you construct the topping of the walls is very important. The pond-liner is layed over the crown of the walls and on top of this you lay one more layer of the material the walls are build of. If you work with brick, cover the top with a layer of solid bricks. If you worked with wood, cover the top with planned boards. In any case it got to be a surface that is suitable for sitting on it, since there is simply no better place to admire the waterlilies from. The maximum height of the walls is 50 cms: that’s 10 cms for the height of the pot, 30 cms water above the pot and another 10 cm for the topping of the walls. A bassin of that kind with a footprint of one square meter and a height of 50 cms will fit even into a small conservatory. When you build the bassin please consider the the pressure of the water. The walls may not be too thin to withstand this pressure. 

In many gardening centers and hardware shops small ready made bassins are available. They are ment for balkonies and terraces but of course they can be used in conservatories as well. 

Needs of tropical waterlilies 

Tropical waterlilies need water temperature of at least 21° C  and a lot of sun, at least 5 hours per day. In no case they are suitable for half shade or even shade. The way you have to treat them depends much on the decission whether you want to winterize them as tubers or keep them as annuals.  

If you treat them as annuals they are planted into 5 – 10 liter pots. Best potting medium is heavy garden soil, preferably with some lome. Avoid organic fertiliser, peat, compost and bark. All of those cause rot that may kill the waterlily. The waterlily needs a lot of fertiliser to bloom well. The only suitable fertiliser is a mineral fertiliser, organic fertilisers cause harm to the waterlilies and even more so to the water by causing algae bloom. We use mineral slow release fertiliser cones like osmocote excat. In those fertilisers the nutrients are release by and by, not all at one time. When we start our tropicals we add two fertiliser cones to every pot. Since tropical waterlilies need a lot of nutrients, it is necessary to feed them regularity with more fertiliser cones. We add every other week one fertiliser cone until September. Treated this way the waterlilies bloom prolific and most of the time several flowers bloom simultaneously. In Germany the flowering period ends when the days become shorter than the nights. Treating tropical waterlilies as annuals may sound like a waste, but you should keep in mind that their price is not higher that the one for a nice flower bouquet. A flowering period of three to four months  exceeds the life span of every flower bouquet by far. 

If you want to keep your tropical waterlily for more than one season and winterize it as a tuber you have to treat it completely different. First of all you have to cause the waterlily stress. A tuber is the reply of the waterlily to stressfull situation, for tubers are the way for a waterlily to survive times of crisis. Stress means first and foremost few nutrients and few space. The waterlily is planted into a small pot, not into a large one. We use 9 cm pots (like the pots perennials are usually sold in, they contain about 2/3 liter) with poor soil as medium. For a start we add just half a fertiliser cone and not more fertiliser afterwards. If you keep a waterlily like this it will stay small and won’t develop many flowers, but it is not flowers what you want. From August on the plant brought into water just 2 – 3 cms deep (for example by rising the pot nd putting it on a stand in the bassin). The waterlily should react on this by forming a tuber. You can stick your finger into the pot and search for tubers under the roots of the waterlily. If not tuber is formed you unpot the waterlily, wash of any soil and let it float in the bassin. Treated like this it will form a tuber in most cases. 

Tubers of tropical waterlilies look like small potatoes. Their size varies from pea size to the size of a fist. The tubers are separated from the plant and are kept in most sand over winter. We keep them in zip-lock bags over winter, but you can also use airtight plastic boxes. The tubers are kept in a dark place with a temperature between 5 – 15 °C. Attic or cellar are usually the best place to store them. 

In March it is time to wake up again the tubers. A 9 cm top is half filled with garden soil and the other half with sand. Plant one tuber into the sand, so deep that it is half burried. The pot is placed in a heated and well lit aquarium that contains so much water that the tuber is covered from about 2 cms of water. Watertemperature should be around 25° C. The tuber will sprout within a few days. In most cases it will sprout more than one plant.  As soon as one of the young plants has developed four floating leaves it can be detached from the tuber by carefully pulling it apart and planting it into a pot of its own. Eight weeks later, in early May, the plants will be big enough to be brought into the waterlily bassin in the conservatory. Now it becomes obvious why the effort with the tubers pays off: from every tuber you get at least two plants. One to produce a new tuber and one that you treat as an annual with lots of flowers. 

Tropical waterlilies in the garden 

Until recently we thought tropical waterlilies in the garden were only possible in wine-growing areas or with heated ponds. In warm summers (2003, 2006) our tropicals grew perfectly in the garden even in water butts without any heating or protection, but this seemed exceptional cases to me. In 2009 there was the first gardening exhibition here at Kirchheim Castle. Being a local nursery we were invited to participate in the exhibition. Part of our exhibition space was a large fountain in the entrance of the castle. A beautiful bassin but with a big disadvantage: the fountain is fed with spring water and there is a constant exchange of water. Even in summer water temperature is just around 15° C. Absolutely unsuitable for tropical waterlilies. We decided to exhibit in the fountain anyway. Our idea was to exchange the lilies every day in the morning with fresh ones. At least one day they should bloom there. When the exhibition was over it was raining and nobody wanted to step into the cold water to get the tropicals out. It kept raining the whole week and soon the waterlilies were forgotten. Weeks later we got a telefon call from the princess: what about the waterlilies in the fountain? Oh no, I thought, they are surely dead and rotten. I asked if it was soon enough to fetch them the following day and was very surprised by the answer: of course, take your time, they are blooming so pretty. A few days later we were standing taken aback at the fountain. The forgotten tropicals were all blooming, despite continous rain and low water temperatures. I learned from this that tropical waterlilies can’t be brought up in cold water but that it is possible to transfer adult potted plants into cold ponds and they will continue to grow and bloom there. 

So there are more possibilities to use tropicals in the garden than we thought before. The precondition is a prepatory culture at at least 21° C water temperature during which the potted adult plant incorportes into the pot. Our clients came up with several clever ideas for this prepatory culture. For example one client placed the pot into a waterfilled barrel and covered it with a poly-cloche (like for tomatoes). Choosing a more sturdy variety helps. Generaly the blue varieties are more sturdy than others, viviparous varieties even some more sturdy. The bassin or the pond for the tropicals should be at the sunniest and warmest spot of the garden. Small bassins or tubs work better than large ponds for they heat up much faster. If you use a black tub the absorption of the sun rays will be more intensive and the water heats up faster.