Category: plants

Preparing the pool for Victoria

Posted on by andy.winfield

Each year at the Botanic Garden, the pool in the tropical zone glasshouse is drained of two thirds of its water and prepared for a new growing season of water-dwellers. The most dramatic of these, is without a doubt, Victoria – the giant water lily. The enormous round leaves, spanning as much as six feet (~2m) across, provide a floating habitat for insects that crawl from leaf to leaf, while anacondas and piranha lurk in the waters beneath. Penny Harms is the Glasshouse Coordinator at the University of Bristol Botanic Garden and she spoke to me this week about what’s involved with providing these native South American giants with the best habitat possible in a northern temperate climate.
As we stood beside the pond chatting, the surface of the water was constantly dimpled as the guppies rose to the surface in search of a meal. The water level is very low, revealing two large wooden planters that sit empty.  The planter on the left, Penny tells me, will contain Victoria cruziana the Santa Cruz water lily – famous for its giant leaves with the strength to support small children.
In its native habitat, in the slow-moving backwaters of the Paraná Basin and in the Pantanal region, this giant lily grows as a perennial. However, here in the UK it is grown as an annual as the plant simply doesn’t tolerate the low light quality and short day length in winter, not to mention the low temperatures in the pool.
“It’s a large plant and very, very greedy,” explained Penny. “It grows at an incredible rate, so it’s easy to grow as an annual and most botanic gardens with tropical glasshouses that display this plant, do so over the summer months.”

Propagating Victoria

It is this time of year, in February, when the seeds of Victoria should be germinated. Propagators will keep the seed over the winter in distilled water and then sow them in small tropical tanks that Penny describes as “glorified washing-up bowls”, which are filled with a very rich loam.
“Really, you’re just trying to replicate what happens in the wild,” said Penny. “The seeds are scattered and are washed up along the edges of the river banks where they settle in very silty, very fine mud. They just sit there until the temperatures are perfect and then they germinate. So, you really don’t need to do much.”
Once the seeds germinate, the plants start growing quite fast. They will be planted out two or three times and when they’ve got two or three decent sized leaves and are in a 40cm pot or so, they are ready to be put into the pond planters. Penny prepares a special mix of soil for the planter that is predominantly loam-based, to which she adds well-rotted manure. She also adds a slow release fertilizer for these greedy plants, which will also be added every six weeks thereafter.
The water level in the tropical pond has been
dropped to expose the wooden planters that will soon
hold the giant water lilies.
The water level of the pond is then raised so that the leaves are resting on the surface and as the plant grows, the water level is raised again and again to accommodate the growing plant.
“Obviously in a pool this size we can’t let it get to the size it would in the wild,” said Penny, “so I remove about one or two leaves a week once it gets going. In this planter, the lily could have four or five leaves, all three to four feet across, but it would all get quite tangled. So instead I reduce it down to about three to four leaves allowing fewer leaves to stay on the plant longer and therefore get bigger.”
The leaves of V. cruzianaare a purplish red colour on the underside and have an impressive network of ribs that are lined with spines. It is thought that these spines offer protection from herbivores such as grazing fish and manatees. The leaves themselves can support up to 99lbs (45kg) of evenly distributed weight, which is facilitated by floatation provided by air that is trapped between the ribs on the underside of the leaf and its distinctive pie-dish rim.

Beetle trapping flowers of the night


Victoria cruziana starts producing flowers after about two months of growth. The flowers open only at night and cast a lovely pineapple smell out into the night air to attract pollinating beetles.
“It only flowers for two days,” said Penny. “The flower will open one late afternoon and be fully open over the night and then it will close during the day and open again a second night, and then that’s it. The little black beetles, which pollinate the flowers in the natural habitat, fly from flower to flower and often get trapped in the flowers when they close during the day.”
While beetle trapping may seem coincidental, it actually serves an important role in the pollination process. The first night that the flower opens it is white and it is its female reproductive parts that are mature and awaiting the pollen carried by the beetles attracted to its scent. However, when the flower is closed during the day it undergoes a sexual transformation and it is the male sexual parts – the pollen laden anthers – that mature. The flower also changes colour, from white to pink, during this process. The trapped beetles get covered in the flower’s pollen as they walk about their petal-walled cell. Then, when the flower opens on the second night, it releases the beetles, which will seek out a new fragrant white female flower. Essentially the plant has guaranteed its pollen delivery system by trapping it!
The glasshouses are definitely worth a visit right
now as the orchids are putting on a wonderful display.
Though the University of Bristol Botanic Garden hasn’t yet propagated its own Victoria cruziana, Penny hopes to do so in the future. Part of the challenge has simply been finding room in the already full propagation house. Proper heaters would also be required to maintain the temperatures needed to germinate the seed. For now, Penny and the horticultural students are already incredibly busy with the preparations needed to plant out the tropical pond.
“There is a lot to do and we have to get things done by a certain date,” said Penny, “because if things aren’t planted out by a certain time, their growing season is shortened. The later you put things in, the longer it takes them to get going and ultimately we want to have things ready for when the public comes in at Easter.”
The glasshouses are of course open to the public now and it’s a good opportunity to see work in progress and to also check out the orchids in the sub-tropical zone, which are putting on a lovely show right now!

The scent of winter

Posted on by andy.winfield

The last remnants of snow that recently blanketed Bristol, and indeed most of the UK, have been washed away by what seems like relentless rain. In the Botanic Garden, the staff and volunteers are seeking shelter in the potting shed and glasshouses, turning to indoor work during this inclement weather. Yet, despite grey skies and soggy soil, the Garden still has some delights to offer the senses.
Prunus mume in bloom at the Botanic Garden
Just outside the welcome lodge at the Botanic Garden, there is a delightful fragrance emanating from the Chinese plum, which is also known as the Japanese apricot (Prunus mume). This is an incredibly important plant in China and Japan and the delicate pink flowers feature prominently in much of the art from these cultures. Beneath the Chinese plum, Helleborus is in bloom – purple, pinks and whites – offering a beautiful winter display of colour.
Andy, a botanical horticulturist at the Garden, has taken time out of his busy schedule to show me around today…in the rain. As we enter through the main gate, all the borders are looking incredibly tidy. Now that the last leaves have fallen, the volunteer and staff gardeners have taken the time to sweep and rake up the remains of autumn.
Snow drops have finally made their appearance.
Andy takes me past the pond to an area at the back of the garden where the gently sloping grass bank is scattered with spring bulbs that have broken through. Andy explains plans to make a bee hotel. There is already a good stack of wood and bamboo started, which will be added to over the next while to provide habitat for solitary bees. There are also plans to use some planks to create a city skyline sculpture that is also fully functioning bee habitat – a ‘Bee-tropolis’ if you will. Good gardeners always treat their pollinators well!
Winter sweet (Chimonanthus) looking a little soggy.
We stop at the winter sweet (Chimonanthus) and have a smell of the small white flowers that are growing along the bare branches. Andy tells me that most of the winter flowering plants are incredibly fragrant in order to attract the few pollinators that are out and about at this time of year. Unlike the sweet smelling Chinese plum, the winter sweet has a more nutty or spicy scent, which makes me wonder what sort of pollinator it’s trying to attract. Generally speaking, flowers with a spicy or fruity smell tend to attract beetles, while sweet smelling flowers attract bees and flies.
The winter flowering honeysuckle (Lonicera purpusii) is in full flower. The flowers are…subtle. In fact, Andy needs to point one out to me. It has a strong citrus smell that is really lovely.
Winter flowering honeysuckle (Lonicera purpusii) 
has a lovely citrus fragrance.

Without a doubt, however, the amazing winter display is the evergreen Daphne bholua ‘Jacqueline Postill’. It is in full bloom and is incredibly fragrant. This species grows wild in the Himalayas and belongs to a group known as the paper Daphnes as the bark was once used to make paper and rope.

Beyond the Daphne, in the corner, there are a number of very large wheelbarrows filled with branches and cuttings that are evidence of how much cutting back and clearing has been done in the garden recently. There is also a pile of branches and a bush, which are all victims of the recent snowfall.
Daphne bholua ‘Jacqueline Postill’
offers an incredible winter display.
“Winter is a time for keeping our fingers crossed,” says Andy, “hoping that everything makes it through and that all the winter protection we did helps.”
As we cruise by the compost heap, I can’t help but think of the rotting robot parts.
Beyond the compost and the vegetable patch, there are piles of Hazel branches. The gardeners have been collecting these in preparation for the new growing season. They are used as pea sticks to support herbaceous plants. It’s one of many winter tasks in the garden.  
Andy explains that winter is when much of the landscaping and development is done in the garden. However, right now with such sodden conditions, it simply can’t be done. But, in the meantime, there’s lots that can be done indoors. Let’s hope the winter pollinators have more luck with their outdoor tasks!

Autumn in a new light

Posted on by andy.winfield

     Some of my fondest memories of autumn are as a child holding my parent’s hands on a crisp afternoon, watching as my little red welly boots swished through the dried fallen leaves of the season. Even now as an adult, I can’t resist shuffling a little when conditions are right, just so I can watch the warm colours roll across my feet and listen to the rustle of autumn. However, last Friday Nick Wray, Curator for the Botanic Garden, opened my eyes to a whole new set of autumn delights – from winged bushes to exploding seed pods – this season is about so much more than just falling leaves.

Fruit and flowers
The small orange fruits of G. tinctoria

     The first stop on our tour was the plant Gunnera tinctoria, which to the untrained eye looks very much like rhubarb on steroids, and as a result is commonly called giant rhubarb. This species is smaller than the one commonly seen in British gardens, Gunnera manicata, but otherwise looks the same. As the plant prepares for its dormant winter phase, the large leaves have started to bend to the ground, revealing a world of colour beneath. Wrapped in a sheath of red feathery tufts are the promises of next year’s growth – buds, which will grow over the winter months ready for next spring. Beside these are the large influorescences, rising up like staffs from the base of the plant. Here, thousands of tiny orange fruits are housed, each one the product of a tiny pollinated flower.

     Growing on the north side of the house, in constant shade, is proof that autumn is still a time for flowers – Begonia grandis. This is a woodland plant from southern China and its pretty pink flowers are only one part of this plant’s colourful display. Turn the leaves over and an extraordinary cinnamon red is revealed.

Flower of B. grandis with the colourful dark underside
of the plant’s leaves in the background. 

“This is an evasion strategy,” Nick starts to tell me, “plants can’t get up and run away from predators, but they can masquerade as something else. Herbivores mooching about through the understory are likely to think there’s something wrong with this plant as the leaves make it look as though it’s dead or dying.”

Nick then takes me around the corner to one of his favourite plants in the garden, Impatiens tinctoria – a balsam. I can instantly see why it’s a favourite as the flower is truly stunning. Native to the mountains of western Ethiopa, this plant is adapted to cold dry winters and warm wet summers. The plant towers above me and Nick tells me all this growth has happened since the second week of May – an extremely fast growing plant indeed!
Flower of Impatiens tinctoria.  

     This plant has been producing flowers since July and they are clearly built for bee pollinators. A deep crimson runway guides the bee toward its nectar reward and as it enters the flower, its back rubs along the anther, dusting it in pollen. The pollinated flowers produce a rather extraordinary seed capsule, which is of course another important aspect of autumn….dispersing the next generation.

Scattering seeds
     Like all balsams, I. tinctoria has an explosive seed capsule. Each one is about 3cm long (just over an inch) and resembles a tiny cucumber. Water pressure keeps the capsule extended, but when a little force is applied, the sides of the capsule spring into their natural curled state of repose and the seeds are literally catapulted out. This explosive dispersal method is partly why Impatiens is very successful as a genus. However, this beauty is not to be confused with Impatiens glandulifera (Himalayan balsam), which was introduced as a garden ornamental by the Victorians and is now found choking many of the waterways throughout the UK.
The bladder-like fruits of Colutea arborescens

     Another wonderful example of autumn seed dispersal in the garden is the Bladder Senna, (Colutea arborescens). Though this plant doesn’t bring any colour to the garden at this time of year, the fruits offer their own element of intrigue. Native to the Middle East – Turkey, Iran, Iraq – the beige fruit resembles slightly deflated balloons dangling from the branches. Open it up, however, and inside you find two rows of perfectly paired little black seeds. As winter approaches, these fruits will fall off the tree and be carried across the dry land by the wind, much like tumbleweed. As the fruit tumbles along, it starts to tear and break down and the seeds get released. This type of seed distribution is very successful, particularly in the seasonally dry climates where it is found.

Losing leaves
     Besides the fruits, flowers and seeds, there is no denying that the Botanic Garden also offers a colourful display of leaves at this time of year. All the autumn colours are represented – yellows, oranges and even vibrant reds.
     As the days get shorter, many plants stop producing a type of plant hormone known as auxin. Among their many roles, auxins prevent a specialised layer of cells at the base of the leaf stalk – the abscission layer – from developing completely and cutting off the internal tubes that connect the leaf to the rest of the plant. So, once auxin levels drop, the abscission layer functionally cuts the leaf off from the rest of the plant. The chlorophyll, which gives the leaves their green colour, disintegrates rapidly revealing the other pigments carotene and anthocyanin, giving the leaves their autumn colours.
The bright orange seed of E. alatus seems dull compared
to the vibrant colour of the leaves

     Nick brings me over to Euonymus alatus, the colour of which almost hurts the eyes. The leaves are a fiery fuschia colour. This species is from China and it gets its name alatus, which means winged, from the hard sharp protrusions from the stem that protect the plant from herbivores. In the summer it’s a pleasant green shrub, but this time of year it is ablaze with colour. If the leaves weren’t enough, scattered throughout the bush are tiny fruits, which have split to reveal a single bright orange seed – a delicacy for birds.

     Other plants, such as the witch hazel, (Hamamelis mollis ‘Pallida’), don more golden hues but are no less spectacular.
H. mollis glowing gold against the evergreen backdrop
of Atriplex humilis (Fat Hen family)

     Nick had to run to a meeting, but I stayed in the garden for another half hour, taking photographs and crouching down to look at plants from new angles and examine parts that are usually hidden by lush foliage any other time of year. It was a whole new way to experience autumn. Of course, I still shuffled through the fallen leaves on my way out…some things are sacred.

Remember – next weekend (26th-28th October) is the 25th British Orchid congress at Writhlington School!