Why does the Waterlily House shut?

The Waterlily House has been a highlight of many visits since it opened in 1852, and there is nowhere else in Kew quite like it - bright, triffid-like plants covering every surface, and the massive Victoria waterlily right in the middle.

But the house shuts every winter, much to the dismay of visitors and staff alike. So why do we shut the whole thing down?

Botanical Horticulturalist Brie Langley answers your most frequently asked questions, and provides an insight into the mammoth task behind the scenes that ensures our display keeps drawing people back.

When does the house shut?

We try to keep the glasshouse open for as long as possible, but after a while the plants look tired and past their best. The waterlilies start to fade as our daylight hours reduce in the autumn.

The giant Victoria waterlilies reduce in size and their leaves don’t last as long. As plants react to the seasons, we must react in turn. That's why we close the Waterlily House throughout the winter months, from November through to April each year.

What happens to all the plants?

We dig up any shrubs, grasses or tubers that we want to keep for next year, which are stored in the Tropical Nursery or the Palm House.

The Tropical Nursery Temperate Unit take cuttings a month or two before we close the house, to ensure we have all the plants we need for next year. These are grown in the nursery so that they are ready to plant in spring.

The old plants are made into compost. Closing the Waterlily House and removing the plants also allows us to reduce the heating inside, saving energy and money.

What about the waterlilies?

Tropical waterlilies are easy to propagate and amazingly fast growing.

The Victoria is grown every year from seed that we produce ourselves. When you visit during the summer, you might see a net bag around one of the Victoria flowers. This is because we’ve pollinated it and want to make sure all the seeds stay in one place.

The bags are collected when we drain the pond, and the seed is germinated in the nursery tanks.

Why does the House shut for so long?

Once the plants are out, the next step is to completely clean all the beds of any soil and drain the pond.

This may seem excessive, but it plays a huge part in our integrated pest management (IPM) programme. IPM is used throughout the gardens as a way of reducing our reliance on harsh chemical sprays.

We clean all the raised beds thoroughly and then power-wash them, along with the windows. This removes a lot of debris, weeds and slime that could harbour pests. The beds are then filled again with sterile compost.

This cleaning is the bit that takes the longest. We need to do a thorough job of it because it will make our lives easier later in the season.

We only use soft sprays, like soap, and biocontrol (insect predators that we release to eat pests) in the Waterlily House. A clean house means that we can start the season with very few to no pests, making any breakouts much easier to deal with.

How do you clean the pond itself?

Every surface is scrubbed and power washed, including all the pots. This helps maintain water quality, as well as reduce algae and pondweed build-up.

The pond is then filled with clean water, ready to start again. We always start this process three weeks before re-opening, as it takes a while to get the water to the stable temperature of 28°C tropical waterlilies need to thrive.

Do all the same plants come back?

Not quite, as the Palm House team completely redesigns this whole glasshouse every year, and each person who does it will bring their own style and flair.

Every year you visit, it should look different. This year is Brie’s third season managing the house, but the first time she has designed it solo.

‘I wanted it to feel fun and carefree, with loads of clashing colours like being in a circus tent. Only time will tell!’

The plants went in ages ago, why not open immediately?

Due to the help of both the Decorative and Princess of Wales Conservatory teams, we were able to plant a little earlier this year, meaning the plants were more settled and mature on opening day.

As well as giving the plants time to grow, we used this time for more pest prevention.

Young plants are often targeted by the maggots of sciarid flies, which live in the soil and eat young roots. With the house shut, we can use sticky traps to reduce the flies before opening.

Once all our work is done, we do one final power-wash to remove all the mud and debris that our hard work has created. Only once the house is completely clean can we re-open.

What’s new?

This year we showcased the world of passionflowers (Passifloras), with many different species creating curtains of flowers later in the season.

The record-breaking Bolivian waterlily (Victoria boliviana) were of course back, with a couple new waterlilies thrown into the mix.

Finally, the entrance was completely taken over by terraced rice fields that were planted successionally, showing a working harvest in action.

These organically shaped terraces were built over a series of weeks using scrap materials from around the Gardens. The shapes were influenced by the terraces of Yunnan province in China, which features beautifully uneven forms cascading tightly down the hillsides.

The rice was planted in three batches, about a month apart, to demonstrate how a working agricultural environment can produce a steady harvest.