It’s been four months without you, the visitors, students, University staff and members of the Garden; four months maintaining a Garden without volunteers, just each other and wildlife for company. Without doubt we’ve all missed you. Missed when the sun shines and people are walking around, some pointing some ambling with their hands behind their backs (also my own chosen method of garden viewing), some sitting with eyes closed feeling the warmth and listening to the chatter of birds around them. On days like this we feel a sense of Gardening for a purpose, when visitors have had an hour away from their usual existence in the company of plants, or taken away new facts and knowledge about the plant world that they’ll forget until that pub quiz, or time has run away from them and its suddenly four o’clock; these all make our work worthwhile. The Garden was built for people to view and without people here it feels a little eerie. (more…)
Category: glasshouses
Sowing Victoria
By Nicola Temple
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| A photo taken a couple of years ago – I have a grasp on my son as he leans over into the tropical pool to get a good look. Victoria cruziana is in flower as is the lotus above us. Photo credit: Shelby Temple |
For me, one of the highlights at the University of Bristol Botanic Garden is the giant waterlily (Victoria cruziana) that lives in the pond in the tropical glass house. Its enormous leaves, which can reach 2 metres in diameter, are studded with spines on the underside and always provide ample wow factor for visiting children (my own included).
The plant is found in slow moving waterways in Brazil, Argentina, Paraguay and Bolivia – in places such as the Pantanal. Its pollination story is an interesting one in that it is pollinated by a beetle (Cyclocephata castaneal). Its white flowers give off a strong scent that attracts the beetles in the evening. The flower then closes around the beetles, trapping them in the flower overnight. The flower produces heat (thermogenesis), raising the temperature as much as 9oC above the ambient temperature outside, which means the beetles can maintain a high level of activity without using as much energy. It’s a thermal reward and the plant benefits as the active beetles will pollinate the flower. The pollinated flower opens the next evening, revealing a new light pink colouration to its petals. The beetles flee the flower and make their way to the next unpollinated flower.
Of course, this species of beetle isn’t found in the Botanic Garden, which makes pollination a bit more challenging. However, there are other insects in the Garden that have filled this niche and the plants have set seed over the last few years. However, this is the first year that staff at the Botanic Garden have tried to sow this seed and, so far, things are going well!
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| The seeds of Victoria cruziana are kept wet. Photo credit: Andy Winfield |
Replicating the natural environment
In its natural environment, the seeds from Victoria cruziana would be buried in the sediments, stirred up perhaps by grazing capybara and swirling river currents. It wouldn’t be until the high water levels following the rainy season had receded that the water temperature and the amount of light penetrating to the sediments beneath would be sufficient to prompt germination.
In the Botanic Garden, botanical horticulturist, Andy Winfield, first primed the seeds by scratching the tough seed coat with secateurs. The seeds were then sown into topsoil and covered with a layer of horticultural grit. The pots with the sown seeds were then placed in a container of water to a level about 10 cm depth above the seed. This replicates the approximate water depth in the natural environment. The water is heated to a temperature of between 30oC and 32oC; this is critical to start the germination process.
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| Andy scores the seeds with secateurs before sowing. Photo credit: Nicola Rathbone |
Victoria cruziana grows around the edges of water bodies and in wetland areas where there is no forest canopy. In order to replicate the amount of daily sun it would be receiving in the tropics and sub-tropics, grow lights on a 12h on/12h off cycle were hung above the pots. Then the whole contraption was covered in plastic film to reduce evaporation and maintain humidity.
Andy had read that germination time is generally about 2-3 weeks in this type of scenario, but within a few days he noticed that the seeds were starting to send out roots and when I visited a week after sowing, the hypocotyledonous stems were clearly emerging from the seeds and shooting upwards toward the surface of the water.
Preparing to plant Victoria out
At the moment, the water temperature in the pool in the tropical glasshouse is only about 14oC, far too chilly for Victoria. In the coming weeks, however, these plants are
likely to grow quite quickly. Andy and the rest of the team at the Garden will pot them on several
times, gradually reducing their water temperature. At the same time, Bristol temperatures will be increasing and the tropical glasshouse will start getting warmer, as will the pool. By the time the Victoria plants have a few decent leaves, the temperatures between the tropical pool and the plants will have become similar enough that Victoria can be put into the planters in the pond.
The annual light intensity here in Bristol is considerably less than Victoria cruziana would receive in South America. However, the long summer days here mean that during those months more solar radiation is received here in a single day than in tropical South America. This helps Victoria cruziana flourish in the Botanic Garden tropical pool over the summer and it will be worth a visit to see it in flower. See the series of photos below taken the day the seeds were sown.
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| Andy prepares the loamy mix for sowing. Photo credit: Nicola Rathbone |
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| The seeds are sown into a loamy mix. Photo credit: Nicola Rathbone |
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| The soil is covered with a horticultural grit. Photo credit: Nicola Rathbone |
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| The seeds are sown and are ready for immersion in a nice warm bath. Photo credit: Andy Winfield |
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| The pots immersed in the warm bath. Photo credit: Nicola Temple |
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| Only one week after sowing, the embryonic stem has emerged and is stretching for the surface. Photo credit: Nicola Temple |
Sources:
Seymour, R.S. and Matthews, P.G.D. 2006. The role of thermogenesis in the pollination biology of the Amazon waterlily
Victoria amazonica. Annals of Botany 98(6): 1129-35.
Victoria amazonica. Annals of Botany 98(6): 1129-35.
Seed sowing at the Botanic Garden
By Helen Roberts
Last month I met up with Penny Harms, Glasshouse Co-ordinator at the University of Bristol Botanic Garden to explore the many different plants they grow from seed. At the end of May the garden staff were nearing the end of a mammoth seed sowing frenzy in preparation for the summer ahead, but Penny explained that seed is continuously sown throughout the year depending on a particular plant’s germination requirements.
We entered the glasshouses via the potting house, which contains a whole range of pots, growing media and tools for propagation. There are different shaped tampers for firming down compost, and numerous dibbers and widgers to gently prick out seedlings. The growing substrate typically used for most seed germinated at the Botanic Garden is a neutral peat-free compost composed mainly of composted bark, coir and composted green material.
Penny explained the finer details of the growing media used, “This compost can be altered by sieving out larger chunks for those seeds that require a finer grade tilth, such as poppy species. Fine and medium grades can be produced depending on the particular size of the sieve pores with perlite often added to help with drainage and aeration.”
Some seeds need constant warmer temperatures
Seed sowing occurs in a number of places within the gardens. Some seed needs a dose of warmth to get germination underway and are sown in propagators in the glasshouses to ensure a stable warm temperature of about 22°C. Others can be directly sown into prepared soil and include many of the ballast seed garden species like Calendula officinalis and Amaranthus caudatus, which form a display in the gardens. Those species destined for the grain barge are grown under glass and have recently been ferried across to the barge and planted. I spied seedlings destined to make the watery journey including Avena sativa (oats) and Eruca sativa (rocket).
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| Some of the Amaranthus caudatus Helen has grown from seed at home. Photo credit: Helen Roberts. |
Back in the warmth of the propagation glasshouses, Penny pointed to a number of seedlings planted at the start of April including the beautiful but very poisonous half-hardy annual Ricinus communis var. gibsonii, otherwise known as the castor oil plant. This species is grown for its dark red metallic foliage and is planted out in the hot border once all risk of frost is past. A dark purple bronze variety of this species, equally as lovely, is ‘New Zealand Purple’.
Penny explained how to grow Ricinus communis, “The species is easy to germinate from seed, but does require a temperature of 20-25°C, so it is best grown in a propagator case in a cool greenhouse where the temperature can be kept stable. Once big enough, it is carefully pricked out and hardened off to then be planted out in June.”
Growing steadily under cover of glass are a number of seedlings destined for the hot border that act as effective border fillers. They include the lovely canary creeper, Tropaeolum peregrinum, a half-hardy annual climber with pale green stems, leaves and yellow flowers, and Tropaeolum majus ‘Black Velvet’, another half-hardy annual with beautiful almost black flowers. Other climbers sown in the glasshouses are the common but wonderfully scented varieties of Lathyrus odoratus (sweet peas). The sunny yellow flowers of Tithonia rotundifolia ‘Yellow Torch’ and Helianthus ‘Mongolian Giant’ currently growing in the glasshouses are also useful border fillers. The latter species is a giant that grows up to four metres high, making it a favourite amongst children. More delicate looking blooms also need the warmth of the glasshouses for germination, such as Digitalis lanata (Woolley Foxglove), which has woolly spikes of fawn coloured flowers with a pearlized lower lip.
Some seed is worth the wait
Some seed germinates very quickly if conditions are right – sometimes within a week – but other seed can be extremely difficult and requires a great deal of molly-coddling in order to get germination success. Penny carefully pointed to a seedling of Cardiocrinum giganteum var. yunnanense, the Giant Yunnan Lily, which as an adult is a beast of a plant and can grow up to 2.5 metres with huge fragrant nodding creamy inflorescences. This species is normally propagated from either seed or by bulbs and can take as long as 4 to 5 years before it flowers. It is a monocarpic species that will die after it flowers leaving offsets, which will then become subsequent plants. This is certainly a species for a patient gardener; it takes a long time to flower but it also takes a considerable time to germinate as Penny emphasised.
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| Blooms of the Cardiocrinum giganteum var yunnanense – the Giant Yunnan Lily. Photo credit: Col Ford and Natasha de Vere [via Flicr CC licence 2.0] |
“This species can be tricky to germinate,” explained Penny, “This one has taken over a year to germinate so it is quite special.”
This is a species that appeals partly due to the fantastic inflorescences, but it has freaky (and rather scary) looking seedpods that resemble vegetative heads with fangs. In my opinion, the lengthy germination and time to flowering is worth the wait.
Tropical and subtropical plants that only survive as mature specimens in the glasshouses can be even trickier to propagate by seed. The seed from Passiflora, a large genus of mostly vines needs to be sown quickly when fresh as dried seed takes much longer to germinate. The subtropical vines of the Aristolochia species, aptly named Dutchman’s pipe, require similar treatment. Species grown at the gardens are A. labiata and A. trilobata, and have beautiful ornate blooms of about 15cm. A. labiata flowers resemble the mottling and coloration of a rooster’s comb. Although tropical and sub tropical species can be a bit trickier to grow up from seed, most species can be sown throughout the year.
Some species do not
need the cosseting of warmth and will happily germinate outside although some seedlings, like borecole (kale), are protected with wire mesh to prevent bird damage particularly from pigeons. Species that have germinated and are growing happily outside at the Garden include the mixed colours of Salvia viridus, more commonly known as the Clary Sage. This produces small spires of lovely flowering bracts loved by pollinators. These are intended for the Mediterranean beds along with the tall spires of Echium italicum, the Pale Bugloss, a beautiful pyramidal plant belonging to the Borage family and Viola arborescens, a pretty violet with large lavender coloured flowers.
need the cosseting of warmth and will happily germinate outside although some seedlings, like borecole (kale), are protected with wire mesh to prevent bird damage particularly from pigeons. Species that have germinated and are growing happily outside at the Garden include the mixed colours of Salvia viridus, more commonly known as the Clary Sage. This produces small spires of lovely flowering bracts loved by pollinators. These are intended for the Mediterranean beds along with the tall spires of Echium italicum, the Pale Bugloss, a beautiful pyramidal plant belonging to the Borage family and Viola arborescens, a pretty violet with large lavender coloured flowers.
Other plants need to be sown at different times of the year and some species have enough flexibility in this that you can sow depending on when you want a plant to flower in the subsequent year. For most gardeners, autumn and spring sowing are the busy sowing months. At the Botanic Garden, for example the open faced flowers of Papaver somniferum, (Opium Poppy), are sown in the autumn.
“These poppies are treated differently to other poppy species,” said Penny, “in that they have been sown in September and will be good strong plants by the time they are planted out the following year, producing flowers earlier than if seed had been sown in the spring.”
Helen Roberts is a trained landscape architect with a background in plant sciences. She is a probationary member of the Garden Media Guild and a regular contributor to the University of Bristol Botanic Garden blog.
Undergraduates get their first glimpse at the garden
By Alida Robey
I’ve been promising myself a visit to the University of Bristol Botanic Garden since I arrived in Bristol four years ago. Life has intervened. Yet when the opportunity came to join the new intake of students from the University on their first practical of their 3 year undergraduate degree, I leapt at the chance.
Once there, the thrill of the plants, garden, stories and mysteries within, were hard to resist! I joined the briefing given by the Garden’s curator, Nick Wray, as he introduced the day’s second group of 70 students (over 250 students attended the practical over two days) to their PhD student demonstrators – there to inspire the undergraduates about different aspects of the gardens.
An introduction to the day
These biology and zoology students were visiting the garden as part of their ‘Diversity of Life’ module – taking a first-hand look at some of the adaptations that have enabled plants to diversify into the more than 400,000 species that exist today. Beyond this, however, the practical offers an opportunity for the students to get to know each other and learn to work collaboratively, gain confidence in sharing knowledge, as well as orientate themselves to this incredible resource available to them.
Nick and the demonstrators were up against time and the logistics of manoeuvring 70 students around 6 ‘work stations’. Students were split into manageable groups and two volunteer guides were brought in to assist moving the groups swiftly through the rotation of topics presented around the garden.
Off we went. As a newcomer myself, I shared the sense of wonderment and awe one student expressed as she exclaimed at how much more there was at the Garden than she had expected. She pointed out how interestingly organised the gardens were, which effectively revealed the story of plant evolution – a set-up that Nick had explained was unique to the University of Bristol Botanic Garden.
Into the glasshouses for plants that eat and are eaten
I followed a group into the glasshouses where Edith showed us the adaptations plants have evolved to cope with extreme habitats. Plants from very different families share common features that are adaptive in similar conditions. Euphorbia, for example, which grows in the deserts of Africa is so similar to the form of cacti found in the deserts of America that they are often misidentified – this is an example of convergent evolution.
The striking Haemanthus coccineus – a native of South Africa -flowers and then sets seed in autumn to coincide with the first rains, giving the seedlings a full rainy season to develop. The leaves appear well after the flowers to reduce the amount of moisture lost prior to the rains. Edith pointed out carnivorous plants that have adapted to nutrient poor habitats. She showed us a plant that produces citronella to deter insects and a species that looked half eaten to make it less attractive to herbivores.
The group was then passed along to Nick who ushered us into the tropical greenhouse to reveal further wonders, such as the orchids of Mexico that require pollination by moths to produce vanilla pods. When commercially produced in the Comoros Islands, pollination is done by hand for every flower – a task often given to children in this struggling economy. We saw the giant lily pads of Victoria cruziana. Reminiscent of triffids, Nick pointed out that in summer they have to be cut back every three days to prevent them growing out of the pond.
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| Nick Wray shows the students the largest seed in the world. Photo credit: Nicola Temple |
Hmmm… time to escape back into the fresh air where things were growing at a more manageable pace for me, but Nick continued to show the group other commercially important plants, such as lotus, bananas and cotton. He held up a specimen of the world’s largest seed – that of the sea coconut or coco de mer (Lodoicea maldivica), which can weigh up to 30 kg.
The students were then taken into an area of the glasshouses that’s not open to the public and shown some very rare and unique plants, including Amborella trichopoda, which is of particular interest because molecular analyses suggest this is one of the earliest flowering plants. It is the last remaining species of a group that first appeared on Earth more than 140 million years ago, when dinosaurs still dominated the animal kingdom. A sprawling shrub native to New Caledonia, Amborelladoesn’t cope with changes in humidity very well, so it is kept behind plastic to control the humidity.
Some students scribbled madly, while others just chose to listen as Nick enthusiastically explained what a unique experience this is for University of Bristol students. ‘Until last year, Bristol was the only botanic garden in the UK growing this plant,’ said Nick. (The University of Cambridge has recently acquired one.)
New Zealand garden – survival of the species
In the New Zealand garden, Dave showed the radical ways plants survive difficult conditions; in this case, the attentions of the now extinct Moa bird. This was graphically illustrated by Pseudopanax, which starts off its first 10 years or so as a sapling with hard, spiky, downward facing sword-like leaves. Once considerably taller – namely beyond the reach of 3m tall Moas – the trees don’t invest as much energy into being unpalatable and transform into an unrecognisably different form, with soft and safely inaccessible leaves reaching to the light.
Angiosperm phylogeny explained
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| A group gathers around the pond to learn about angiosperm phylogeny. Photo credit: Nicola Temple |
I moved on to hear about angiosperm phylogeny; a new term for me, but more exciting and less daunting than it sounds. In the past, plants were classified into family groupings based on their physical characteristics. With the advent of DNA sequencing in the last 20 years, we can use genetic relatedness to help us understand how plants have evolved. James, our demonstrator, pointed out some of the oldest species of flowering plants, including star anise (Illicium verum). This area of the garden is organised into the two major groups of flowering plants monocotyledons (seed has single embryonic leaf) and dicotyledons (seed with two embryonic leaves). The monocots include plants such as orchids and grasses, including agriculturally important species such as rice, wheat, barley and sugar cane. The more familiar garden plants, shrubs and trees, and broad-leafed flowering plants such as magnolias, roses, geraniums, and hollyhocks are dicots.
Learning in the garden beats a textbook any day
Speaking with the students, they said they enjoyed being able to touch and feel the actual plants, make comparisons and learn within this physical context. They could see as James explained how even though Protea, lotus, Banksia and London plane tree (Platanus x acerifolia) looked very different, their DNA suggests they are more closely related than they appear. Genetic relatedness is traditionally illustrated using a cladogram – a branching tree with scientific names at the end of the branches, with no sense of what these species look like. What an opportunity to see what the diversity at the end of those branches can look like!
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| Students use pens to see how flowers are adapted to distribute pollen on the pollinators that visit them. Photo credit: Nicola Temple |
My time ran out before I could get as far as the sessions on pollination and plant evolution! With my head spinning from this intensive and whistle-stop tour of some of the delights and extraordinary features of this garden, I sat on a bench in the autumn sunlight to reflect on the afternoon with fellow blogger, Nicola Temple, who had invited me take part in this day.
Like many of the students I spoke with as we went from location to location, I was delighted to have had the opportunity to understand the great thought behind the layout of the gardens. There was far and away more here than I had bargained on. I wanted to keep going but knew I could only take in so much on my first visit. As we had gone around I had been surprised as an observer to note how quiet the students were, very few asking any questions. Having stood back from it though I wonder if, like me, they were overwhelmed by the hidden depths to this exceptional garden. I’m certainly going to seek every opportunity to spend more time here, whether learning or simply enjoying the peaceful and stunning surroundings.
And I daresay I will come across many of the students from this day, pursuing their studies and enjoying the sheer delight and boundless wonderment that nature continues to shower upon us and that this garden so beautifully illustrates.