The plant conservation centre is a centralized propagation and nursery facility for the National Trust, and to a lesser extent, other organizations. Formerly based at a trust property, the decision was taken to move a few years ago. The centre has biosecurity at its heart, and a systematic approach to this. Thus, these facilities require specialist siting and design.
The site should be fairly isolated, with a buffer zone from potential contaminants, ideally a natural cordon. This isolation should be balanced with the need for access to infrastructure. A site with high air flow is desirable, as many disease risks are lessened when air flow is increased. Future developments also need to be considered, so the site can adapt and expand as necessary.
The site aims to be fairly self sustaining. Rainwater is harvested and stored underground. A borehole was also made to complement the rainwater harvesting. The water is filtered and then treated with ultraviolet light, and is pure enough to drink.
Quarantine areas exist as another cordon to reduce the risk of disease. Herbaceous plants generally have a lower risk of serious disease than woody specimens. Good practice entails inspecting roots, vine weevil being one example. Test kits are used, particularly for more serious diseases. Higher risk plants monitored for 6-8 weeks, fully contained, with minimal contact. Knowledge of diseases, their hosts, and malevolence is vital
When entering the nursery, any soil is removed with particular attention paid to footwear. Footbaths are used for disinfection. Cleanliness and hygiene is vitally important, as is the design of the system. The system should have a perfect flow, innately reducing the risk of cross contamination.
Mist units are used for some propagation. Small batches are used. Different light conditions are provided for different plants, as well as other environmental factors. Micro propagation is used for certain plants, particularly if plants contain infection. One method involves paring a flower bud, cleaning and sterilizing it, before placing it in agar and inducing growth through the introduction of growth hormones. Some plants may require a 10 year investment if micro propagated. This longer term thinking is key to successful conservation.
Curators of plant collections need to document their plants, and divide these into significance. Plants can be significant for different reasons. I was reminded of the wealth of plants of cultural significance that exist, and the importance of sharing this knowledge. Digitally documenting this knowledge needs various resources and collaboration. However, a universal database of significant plants and the digital sharing and evolving of this knowledge seems to me to be one of the most important things we could do.
The movement of plants from an agar environment to compost is a difficult stage. Potting substrate is specially made to order, and can be tailored to specific plants. Airpots are used to promote a root structure adapted to spread, rather than becoming spiraled and pot bound in closed containers. These do require more frequent watering however. A drip system is used in the nursery to remedy this. Bark mulching of pots is used to reduce weeds in the nursery area. A clean room is used to sterilize any propagation material. Material is soaked in 20% bleach solution for 2-3 minutes, and physically cleaned.
We saw a grafting system influenced by commercial designs using hot pipe grafting. Grafting needs to be undertaken in periods of dormancy when sap flow is reduced. The production window for grafting has become shorter as climate has warmed. A union usually forms within 2-3 weeks. Temperature required varies by plant, but 15°C is a good average. Various grafting unions are used. Finding appropriate rootstocks for the scion, in terms of size and characteristics is an important consideration.
The substrate is comprised of bark fibre and wood chip, with coir being available as well. Air pots can increase the speed of plant production, and also have particular suitability to conifers. Foliar feeds are used to supplement nutritional requirements, as well as drip feeds. Air pots are recycled where possible, being sterilized before entering the nursery environment again. Hortisept pro, Propeller, and Cleankill are recommended disinfectants. Wood fibre pots are also used, reducing the use of synthetic materials. Peat free composts seem to respond best to watering little and often.
Plant sourcing for our gardens is an important issue. Developing relationships with suppliers is key. This can be a challenging issue, particularly in the sourcing of rare plants with a limited supply. Ideally the relationship should be a close one, but sometimes this is limited by simple geographical distance. A nursery forum may one way of solving this. The trust has a wealth of knowledge within, and with digital communication the infrastructure being there, it may well be a case of just having enough more time to invest in collaboration.
In terms of nurseries, a review system shared internally may be a great thing. Supporting and developing relationships with the best nurseries, whilst avoiding those that are poorest. The importance of exciting plants, modern and historic, and the quality of their initial cultivation is paramount to successful gardens. The PCC is a fantastic resource with incredible potential to be an internalized supplier of interesting plants. Sharing of plant material from other properties could be seen as a dilution of character. However, I see it as the opposite. Properties have overlapping histories punctuated by notable plants. These may serve towards embellishing plant collections, increasing the genetic reserves, and engaging more people with plants and their stories.
The PCC has a collection of limes, with varying habits, some suited specifically for use as avenues. A collection of Buxus from Ickworth is also held. The need for long term thinking is essential.
3500 plants have been propagated this year, ready for delivery over the next few months. All plants are databased, so individuals can be traced, and plant movements are transparent. Heeling in plants on arrival at properties, with good aftercare may be best practice. If planting needs to be delayed, this allows plants to adapt to the garden’s growing conditions.
The production house is an interesting structure. Seeing all the plants lined up, ready for delivery is impressive. The structure is shaded to avoid summer extremes of temperature. The sides can be rolled up necessary, with top fans able to extract warm air, and others used to reduce stagnant air. Plants, such as marigolds, are interweaved with plants to attract and feed biological controls. Successful biocontrol requires regular monitoring of pest and control populations, and also of environmental control to provide an ecosystem swung in favour of the predators. Biocontrol is becoming more affordable. With increased knowledge, biocontrols are becoming more important in integrated pest and disease management, serving to reduce the reliance on synthetic chemicals.