Glasshouse Water Gardening in the United Kingdom

 By Harry Hutchings BSc. AMPS Timberland Watergarden

This article was originally published in the International Water Garden Society journal, The Water Garden Journal, and has been published on this site with the kind permission of Harry Hutchings and the International Water Garden Society 

The United Kingdom (UK) climate is not suitable for tropical waterlily cultivation outdoors. Please, however, do not overlook the beauty of these plants. It is not too expensive to create a stunning display.
I have 5 glasshouses of sizes from 6 ft. x 8 ft. up to 12 ft. by 24 ft. I also utilize the much cheaper poly tunnel option in which I have many 1m x 3m fiberglass tanks as used by aquarium and pond suppliers to keep their fish. However, the glasshouse pond gives the more presentable display.The Harry Hutchings tropical garden plan
A good size as a start is 10 ft. x 12 ft. Please avoid the cheap spring clip glazing types. Go for the glasshouses with strip sealed glazing. These have better security against high winds and also have a construction that allows the use of the expanded polystyrene sheets for internal insulation.
A pond needs to be excavated and a liner used. Choose butyl with under liner if you can afford it. If not, at least choose a liner that will withstand a lot of foot traffic. Your tropical lilies will need a lot of attention, as you will see later.
If you can, orientate your glasshouse with your door facing south. This will allow the garden section to be on the north face, which is essentially at the back. Construct the pool size 8 ft. wide by 10 ft. long. 18 inches deep is sufficient for most tropical waterlilies. A margin of 15 inches at the back is filled with a mixture of peat and sterilized loam based topsoil. The side 12-inch wide strips are filled similarly. A front 9-inch margin is to be used for the equipment. I construct the pool using 3 inch deep x 2 inch wide treated softwood to form the frame to which I nail the liner...this allows me to use “decking” cut to 9 inch lengths for the front equipment strip. Using a similar strip of treated wood as the front support, I insulate the north face (the back) and the east and west (sides) back panels with white expanded polystyrene sheets. Those sold in the trade-building store around 1/2-inch thick you will find slide nicely into the internal upright pillar recesses. This is not possible with the cheaper spring clip glazing models I mentioned earlier. I also cover the back two roof panels either side with UV protected bubble polythene sheeting using twist ties to secure it. Despite the UV protection treatment, this will need replacing every few years so have some planks of wood handy to span the pond for this maintenance. I incorporate self opening windows with a special wax compound (orchid wax). The wax supplied with the glasshouse generally opens at too low a temperature for the air bubbling technique discussed later. Your garden surround will contain various tropical plants.

Temperature charts illustrating the advantages of the strip of black linerYou will need a submerged pump delivering around 500 - 1000 liters per hour with a 1/2-meter head pressure. A 9-volt UVC unit, a 4-outlet air pump with tubing and 4 air stones, 3 of the 300-watt aquarium heaters and domestic dehumidification unit. All of these will need power with RCD protected waterproof connections. The pump, UVC and heaters should be able to be switched off when work is done in the pool. The air pump and dehumidifiers can be on a separate circuit.
The reason for the various pieces of equipment is as follows… The heaters are spaced apart on a wire support across the centre of the pond as heat backup and for extra heat if required for an early season or late season extension. The air pump uses the hot air inside the glasshouse to raise the water temperature. This reduces the need for the more expensive use of the 3 water heaters. Listed below are 2 examples of a UK day in August and the effect of the air pump in raising water temperature. The effect can be further enhanced if a strip of black liner is placed on the north side to capture further sun heat. As the air pump is only used when internal air temperature exceeds the water temperature, the air pump should have its own switch. It can also be equipped with an on and off timer switch. The pump is placed at the back of the pond and returning the water at the front via the UVC unit for algae control. This gives a more even temperature mix to the pond. The dehumidifier reduces condensation and returns de-ionized water to the pond.

I use 2 night blooming waterlilies in the back of the pond side by side. My own hybrid of Nymphaea ‘Red Flare’ x Nymphaea ‘Antares’ and N. ‘Antares’ itself. Both are red and both are contained in their growth and runner formation. They bloom constantly and don’t seem to mind the lack of sun here. I have Nymphaea ‘Mrs. George Hitchcock’ as the centerpiece. It has huge pink flowers but needs to be kept in check. Another possibility would be a less space stealing night blooming waterlily such as Nymphaea ‘Brazos White’. In the front I have 3 day blooming waterlilies that are not greedy for space. Nymphaea ‘King of Siam’, Nymphaea ‘Miami Rose’ and Nymphaea ‘Pamela” This gives me a deep purple, a rich pink with marmorated pads and a light blue. Choose your own varieties but don’t expect the star varieties to stay within their area. With a restricted space such as this, you must regularly trim off leaves that spread too far and those that are beginning to die. I leave around 8 leaves though to ensure continuous blooming. In my bigger glasshouse, I use Nymphaea ‘Foxfire’, Nymphaea ‘Star of Zanzibar’ and Nymphaea ‘Golden West’ all of which need more space
The garden surround contains the tropical terrestrial plants. At the back, the main plants are cannas. Choose those that grow to less than your glasshouse height. Some grow to 12 ft tall. I then have 3 different colored lantanas and 2 datura that bear pure white, large flowers that reseed them selves every year. I add morning glory and other climbers that all self seed every year to fill the gaps. On the side strips, I use plants no more than about one foot high. I have found some glorious miniature hibiscus plants with huge flowers that keep at about 1ft. high and some annual verbenas. You will have your own ideas.

The man himself: Harry HutchingsI use pots without drain holes that I pick up from the supermarket flower section They are used to transport and display cut flowers. They are about 10 inches deep and 8 inches in diameter. Failing pots with no holes, I use a similar sized pot with the drain holes covered internally with corrugated cardboard and a 1-inch layer of clay soil to form a barrier to avoid fertilizer leaching into the water. The soil is a mixture of peat and loam mixed with bone blood, fishmeal and slow release 11.11.18 fertilizer beads up to half way. Then a mixture of my sandy topsoil and sterilized loam in which the plants are allowed to establish before hitting the fertilized layer which might burn new roots. Every 3 to 4 weeks I push 3 of the 7.5-gm. 15.9.9 fertilizer tablets deep into the pot using a dibber if necessary.
In addition to the dehumidifier with the return pipe feeding back the condensation water, rainwater should be added to keep up the pool level. The surrounding plants will also need watering every other day and kept fertilized with a high potash fertilizer. The accompanying photos and diagrams illustrate the concept.
It is necessary to get into the pond regularly to prune back excessive leaf growth...fertilize the waterlilies and the surrounding garden and to remove old flower heads. All electrical activities are turned off and I have a wader outfit when doing plant maintenance. Take care to ensure no sharp objects are stuck in the treads of the boots for this purpose.