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Monday, 25 January 2016

To grow or not to grow: plant propagation at the Botanic Garden

By Helen Roberts

At the start of December, I met up with Penny Harms, Glasshouse Co-ordinator at the University of Bristol Botanic Garden, to discuss the plants that are propagated at the Garden and how this valuable work is carried out. Over the course of the year, I will be investigating the different forms of propagation techniques used in the Garden to maintain and enhance their existing stock of plants. I will cover briefly how these techniques are carried out (bearing in mind that there are a plethora of books available on plant propagation), but I'll also examine what is happening at the cellular level and examine the 'why' behind certain propagating techniques.

As Penny and I examined some seedling plants, she explained to me why propagation is so important at the Botanic Garden. "If we lose some plants outdoors in a cold wet winter, we have a back up of new plants. Some are not simply insurance plants, but are taken as cuttings as a necessity every year as they survive in our climate as annuals, particularly those plants from the South African collection. Others, such as the Mediterranean plants, do not survive as long here in Bristol as it's generally much wetter and therefore they need to be replaced fairly frequently. Most plants we take from cuttings are mainly tender perennials and frost tender plants."

Propagation in the Garden won't likely restart until the spring depending on weather conditions.

In the glasshouses, Penny showed me many of the plants that have been propagated from cuttings, including some beautiful decorative Aeonium species (commonly known as tree houseleek), as well as Pelargonium (geranium), Clematis, Salvia and Passiflora (passion vines) species. Some plants raised from cuttings  are placed in a unit that is misted with water regularly and the bottom is heated to a temperature of 25°C in order to encourage roots to form. The plants all looked wonderfully healthy, not at all like my puny looking specimens that I had taken cuttings of back in September at home. However, the plants that really caught my eye were some small fern plants potted up, which Penny called "fernlets".

Ferntastic ferns

Ferns belong to the plant division of pteridophytes (spore-producing vascular plants) and are extremely diverse in habitat, form and reproductive methods. Most ferns grow in moist warm conditions and very few tolerate dry cold places. Although they aren't flowering plants, the frond shapes and colours can be exquisite. Closer inspection of the undersides of the leaves reveal beautiful patterns of sporangia - the vessels containing the spores.

Fern reproduction 101

Fern lifecycle
Image credit: Carl Axel Magnus Lindman
[CC BY-SA 3.0], via Wikimedia Commons

Like other plants, ferns have alternating haploid (single set of chromosomes) and diploid (two sets of chromosomes - one from each parent) generations; the haploid gametophyte produces the cells for sexual reproduction while the diploid sporophyte produces spores that produce the gametophyte. Unlike flowering plants where the gametophyte is reduced to the pollen and embryo sac, fern gametophytes are free-living. (Although they are admittedly less conspicuous than the sporophyte we generally identify as ferns.)

In brief, the sporophyte produces spores, which are shed and grow into gametophytes (also often called the prothallium). In some species, individual gametophytes will be either male or female, while in others an individual gametophyte will function as both sexes. When the conditions are right, the gametophyte releases mature sperm from the antheridium, which swim to the egg-producing part called the archegonia under the gametophyte's underside. Fertilisation produces a zygote, which develops into an embryo and eventually outgrows the gametophyte to become the sporophyte.

The plantlet sailboats on the fronds of Woodwardia prolifera.
Photo credit: Andy Winfield.
Like many other plants, ferns can also reproduce asexually through branching of the underground root stem or rhizome. Some species will even produce leaf proliferations known as plantlets or offsets, such as the beautiful Woodwardia prolifera, which comes from Asia and grows in coastal regions. It's small plantlets (or "sailboats" as Penny calls them) drop off the plant and fall to the ground, securing themselves quickly with their roots.

Fern propagation at the Botanic Garden

Fern spores are carefully collected when the ferns are sporolating by cutting fronds and letting spores fall into paper bags. Spores are only collected when they are ripe; usually the sporangia will swell and will turn brown, black, blue or orange depending on the species.

"As far as when to collect the spores," said Penny, "it is really a case of watching and waiting. The beautiful orange [sporangia] on the Phlebodium aureum var glaucum go a slightly darker brown when they are ready, which makes it easier to know when to collect. And if you lightly tap the frond over some white paper you can watch to see if the spores are being released."

The underside of a frond from Phelbodium aureum var. glaucum,
showing the sporangia. Photo: Andy Winfield.
Penny added that she often collects additional spores by simply placing a fern frond onto a tray containing already wetted peat-neutral compost with bark mulch to allow spores to drop onto the substrate. Penny had great success growing new plants from spores harvested from a miniature tree fern species called Blechnum gibbum. This plant was looking in a sorry state before the move to The Holmes at Stoke Bishop and so Penny collected spores just in case it didn't survive the move. However, research revealed that this fern was behaving like a deciduous plant -it had died back, but wasn't dead. Thanks to Penny's careful propagation, the glasshouse now holds a number of specimens from this species - all grown from spores of the original plant.

The tree huggers

Some the glasshouse ferns are also epiphytic and will reproduce effectively from spores. One such example is Stenochlaena tenufolia, a South African fern that will grow up trees. Its climbing rhizome can reach up to 20m in length and 15mm in diameter. As young plants, they start off on the ground, but soon start to ascend trees, trading in their connection with the soil for life in the trees. Often plants don't produce fertile fronds until the rhizome has climbed sufficiently to expose the apical region of the plant to sufficient light. These ferns are grown both from spores and vegetatively at the Botanic Garden.

The runners

Other species require a different approach. Diplazium proliferum, a fern that is widespread in the tropics and subtropics, produces little rooting plantlets along its fronds that can be developed into new plants. The frond is simply cut and laid onto bark mulch, pegged with wire and then half buried with the substrate.

The chain fern, Woodwardia radicans (from the Macaronesian region but also found on other Mediterranean islands) also produces bulbils but these are usually located at the ends of the fronds as a hard nodule. The roots start to develop in the air but when they touch the ground will root into the substrate and form new plants.

Penny explained, “We got these plants from Tresco where they grow as huge sprawling mounds. The small bulbils eventually form quite large plants, but are still connected to the original. This gives this fern its very relevant name. New plants can simply have the connection cut and be dug up and transplanted elsewhere."

A brief step-by-step lesson on how to propagate ferns

At the Botanic Garden ferns are being propagated very successfully, but there is no reason why horticulturists at home should not be able to have the same degree of success. Penny offers her expert advice in propagating ferns by spores below:

Ferns can be propagated vegetatively, by division, or similar to sowing seed from flowering plants, by spores, which are found on the underside of the fern fronds. Some fern species are very difficult to propagate from spores, however Adiantum, Pteris and many Blechnum species are reliable.

Here are the main points for the propagation of cool glasshouse ferns from spores:
  1. The spores should be collected when ripe. The sporangia found on the underside of the frond, will (in most cases) change in colour from a light to dark brown to indicate the spores are ripe. To check, lightly tap the frond to see whether the tiny brown spore cases (sori) are released. If so, the fronds can be cut and gently placed into paper bags in order to collect the fine sori ready for sowing (see point 2) or the frond can be cut and placed directly onto the surface of a pre-prepared tray of compost, allowing the spores to fall naturally as the frond dies away. 
  2. Sow the fern spores. Collect the spores from the bottom of the paper bag and sow immediately. Fresh spores will germinate far more successfully than ones that have been kept for some time and dried out. Use clean, shallow, pots and/or trays with drainage holes. Place a fine layer of gravel on the bottom. Add a layer of peat-free, fine grade compost and gently firm down. Stand the pots and/or trays in water to allow the compost to absorb the water. When the compost is wet, lightly and evenly sow the spores over the surface of the compost. The spores are very fine and on no account should they be covered with more compost, as this will prevent them from germinating.
  3. Keep moist. The trays and/or pots should be covered either with a propagator lid or glass and stood in a shallow tray of water. It is important that the compost does not dry out. 
  4. Position in a semi shaded spot ideally at temperature of 16 - 20°C.
  5. Once the spores start to germinate, the young fern plants (prothalli) should become visible within a couple of weeks. Allow the prothalli to establish themselves for a little while before moving on to the next stage, that of pricking out the delicate new plants.
 Moisture is the most important element for the successful propagation of ferns. 

Tuesday, 19 January 2016

Saving our nation’s lost landscapes

By Helen Roberts

Historic gardens are an integral part of our cultural link with landscapes; a place where we can connect with nature. They represent a form of artistic expression and illustrate snapshots of past ages, cultures and societies. For that reason alone these garden masterpieces deserve recognition and preservation. 

Often the final level of protection for many of these gardens falls to English Heritage, a registered charity, independent of government since April 2015, which essentially acts as guardians for the upkeep of some 400 historic sites. English Heritage is often seen as the last resort of protection for these sites, some of which are so special that the government has stepped in to look after them and rescue them for the nation. 

Late last year the Friends' Lecture was given by Christopher Wedell, a former trainee of The University of Bristol Botanic Garden (21 years ago) and now senior gardens advisor to English Heritage. 

Bridge in Sheffield Park Garden.
Photo credit: ReflectedSerendipity
courtesy Flickr [CC BY-SA 2.0], via Wikimedia Commons
Christopher’s horticultural career began early; as a teenager he already expressed a keen interest in the outdoors. A stint of work at Sheffield Park in Sussex fuelled his passion for horticulture and historic landscapes and led to a degree in Horticulture at Writtle College with a final year dissertation on historic gardens. After his work at the University of Bristol Botanic Garden and Tylney Hall, Christopher obtained his Kew Diploma in Horticulture and then spent 18 months working in the famous Palm House. From Kew he went to Wisley where he eventually became superintendent under curator. When a 6-month contract offered itself at English Heritage he applied and 7 years later he is looking after 23 historic and contemporary gardens ranging from Elizabethan to contemporary in design.  

Christopher spoke in detail about the gardens under the care of English Heritage, the complexities of restoration and the many challenges the team faces when completing historic garden works. 

The importance of authenticity

The restoration of historic gardens is a difficult task in itself when there is a lack of historical information in the form of maps, descriptions and documents. Often gardens are multi-layered over time, making it difficult to know at what particular point in time to restore the garden to. 

Belsay Hall, a thirteenth century site located just north of Newcastle has magnificent Grade I listed gardens and were primarily the work of Sir Charles Monck (1779-1867). He was influenced by the Picturesque movement, which sought to create landscapes less conventionally beautiful and more naturalistic in design. The restoration of the unique Quarry Garden, a dramatic place with a special microclimate with many exotic trees and shrubs, presented English Heritage with a challenge of maintaining the correct authenticity. To achieve this, the team used a number of photographs collected over the decades to aid in the restoration process.

"Photographic and historical documents are very important in the restoration process," explained Christopher, "and it is vital that as much historical information is collated as possible, thereby restoring the landscape at the most significant point in historical time". 

Osborne House from the road to Swiss Cottage.
Photo credit: By Loz Pycock from London, UK
[CC BY-SA 2.0 ], via Wikimedia Commons
Sometimes, as gardens change over time, plants become over-mature and cease to provide the effect for which they were first planted. English Heritage faces a number of challenges with such restoration projects because people often develop strong attachment to these mature trees. One such example includes Sovereign Avenue at Osborne House on the Isle of Wight - the private home of Queen Victoria. The avenue was planted in 1851-1854 with two lines of alternating deciduous and coniferous trees. Over time (as expected), these trees matured, but eventually became too large and made the avenue dark and oppressive. This was not the intention of the design when planted by Prince Albert. English Heritage then faced the challenge of how to visually present this avenue with the possibility of replanting every 50 years to maintain authenticity. 

Maintaining the fabric of the garden

The fabric of a historic garden represents the context in which a garden is situated. Gardens do not simply exist as islands on their own but connect and integrate with surrounding landscapes to create cohesion and robustness, both of which are sought after qualities in designed landscapes. Often it is difficult to maintain connectedness in historic landscapes due to the simple issue of land ownership. 

One such English Heritage example is that of Audley End House, a Jacobean Mansion landscaped by Lancelot ‘Capability’ Brown and set within the rolling countryside of Essex. English Heritage has in their care the mansion and grounds itself, but also a tower located outside of the boundary of the mansion grounds some distance away and the land in between is not under English Heritage ownership. Here, English Heritage faces the difficulty of maintaining a connected landscape, as the sites are geographically distant from one another, but sit within the same landscape. Belsay Hall also faces similar challenges as the existing car park is set within the historical landscape fabric, which disrupts the harmony of the site. 

The visitor experience

It can be difficult to maintain a good visitor experience all year round in many of the English Heritage gardens. Many of the gardens are very seasonal in nature as bedding schemes took precedence over year-round interest. At Kenilworth Castle (just north of Warwick) an Elizabethan garden was created by Robert Dudley, Earl of Leicester in order to seduce Queen Elizabeth I when she was staying at the property for a mere 19 days. This garden was restored in May 2009 using advances in garden archaeology and the survival of a fascinating eyewitness description from 1575. When the garden was originally designed for a short spell of interest, English Heritage now faces the difficult task of creating a garden that is attractive to visitors throughout the year. 

To attract visitors to the gardens, many English Heritage sites hold contemporary art exhibitions, such as the one held at Belsay Hall called ‘Extraordinary Measures’ with many of the installations located in the grounds of the Hall. 

Other attractions to entice families have recently been sensitively incorporated into some historic landscapes. An imaginative wooden play structure for children has proved very popular at Witley Court near Bromsgrove with a tree house in the form of a seed pod, outdoor musical instruments and wobbly bridges, scramble nets and slides. The opening of the beach at Osborne House on the Isle of Wight has been well received with people enjoying swimming, paddling, building sandcastles and looking inside a bathing machine. With the opening of access to the beach though, English Heritage was then faced with the challenge of incorporating essential utilities, such as power and water, into a historic landscape. Other interesting plans for enhancing the visitor experience described by Christopher included the potential restoration of the unique hard tennis court at Down House, home of Charles Darwin, which would provide a great play facility for adults and children alike when visiting this historically significant place. 

"It’s really important that sites do not simply stagnate in terms of a design sense and that the gardens are able to evolve and be used imaginatively," explained Christopher. 

Many sites have successfully integrated contemporary spaces into the gardens adding a new vitality to these historic places. A new contemporary garden was added in 2000 to the kitchen garden of Osborne House by designer Rupert Golby as part of the contemporary heritage garden project. It includes many plants with names associated with Albert and Victoria. 

The future

Christopher’s message was clear throughout the talk. These gardens need to be brought to life for current and future visitors and be places that continually thrive for decades and centuries hereinafter. 

Christopher emphasised that, "English Heritage is playing a vitally important role in looking after these sites; we are the landscape custodians helping to safeguard some of England’s most treasured historic gardens."

The next Friends' Lecture will be given by Nick Wray, Curator, University of Bristol Botanic Garden on 21 January 2016, Frank Theatre, Wills Physics Laboratory from 7:30pm - 9:00pm. Nick will be speaking about the ballast seed garden project. Friends are free with presentation of membership card; non-Friends will be asked for a donation (suggested £5).