Saxifraga all the way – May 2024

From the highlands of Scotland to the lush gardens of Oxfordshire, my traineeship journey this month has been all about Saxifrages! It began in the highlands, working alongside the team in charge of Scottish native plants at RBGE, gathering Saxifraga hirculus and assessing prospective translocation sites. This adventure continued at Waterperry Gardens in Oxfordshire. Here I had the chance to help and learn from Adrian Young. He is Collections Manager for the Plant Heritage National Collections of Porophyllum and Ligulatae saxifrages.

Collecting wild saxifrages in the highlands

In early 2023 RBGE started a project to restore ten Scottish plant species. One of the ten was the marsh saxifrage, Saxifraga hirculus, which is threatened by habitat loss and climate change. This lovely yellow-flowered saxifrage is rather fussy, especially in cultivation. It has seldom been grown for longer than two years. The plants need particular water chemistry, temperature, and flow rates to ensure good oxygen supply to their root systems. The team have replicated these conditions back in the nursery at RBGE by creating a 10m long cascade of flowing water. Plants grown here will be propagated to increase numbers. Eventually, these new plants will be relocated into the wild.

I was keen to become involved in this project, while working here at RBGE, so I jumped at the the unique opportunity to head to the highlands and gather S. hirculus plant material. This adventure with Becca Drew and Emma Beckinsale enriched my understanding of the growing conditions marsh saxifrages require.

A large proportion of the plants were thriving in dense moss, surrounded by low growing vegetation. A steady amount of water flows through the boggy ground. What I found interesting is how vital water flow was. To grow well, plants needed just a slow trickle. Where water was flowing faster, less plants were found. We visited a number of translocation sites to assess conditions, such as water flow. All of this will be taken into account when selecting potential planting sights.

During the trip, we collected over a hundred plants from various locations throughout the highlands. We made sure this would not put the populations at risk by over-collecting. We only took plants from areas with a high amount of material and from various locations, rather than lots from just one site.

At first we flagged up any plants we planned to collect. We marked each plant with a flag until we were satisfied they were evenly spaced out, to ensure we would not put the colony at risk. We numbered each plant, collected data and took photographs of each individual. We then went along with a planting knife carefully digging out each plant and placing it in a 7cm pot, labelled with its collection number.

Back at the nursery they were planted into the cascade to replicate the conditions which we had witnessed in the highlands. It should not be long before these plants have bulked up and can be divided.

The National Collections of saxifrages at Waterperry Gardens

Later in the month I was fortunate to head south to Oxford to work with Adrian Young. Adrian is a fountain of knowledge of all plants but especially the genus Saxifraga. What he does not know about saxifrages is not worth knowing. I learnt a tremendous amount from him as he is so generous.

Adrian showed me his technique of taking saxifrage cuttings. He uses sand with round particles, sourced from a local sand supplier in Leighton Buzzard. We also added a small proportion of vermiculate to help retain moisture. The seed tray was filled up by half and tampered firmly using a board, then a thin layer of sand was sieved on top and dampened with water. Sieving the top layer of sand gives the cuttings a better chance to make full contact with the sand.

Adrian recommended taking cuttings with 1-1.5cm of stem and for any old roots to be cut off. Doing this will help to stimulate rapid fresh root growth. We also removed any dead foliage from the rosette. A square-ended chop stick was used to make a hole in the sand. Once the cutting is placed in the hole, the sand was firmly pressed around the cutting with the square ended chopstick, to ensure good contact between cutting and sand. The tray of cuttings was then moved to a shady area of a greenhouse and sprayed with a fine mist. It will be checked regularly, making sure the sand is moist at all times.

Climate change makes growing certain plants a real challenge. This is especially true for the Porophyllum saxifrage group. The area where Adrian grows his collection is situated in the walled garden at Waterperry. Being surrounded by old walls, built in 1760, gives the area much warmer growing conditions. He has made lots of changes to the way he grows the Saxifraga collection now. One of these changes is shading. Wooden structures have been built over the collection beds, 2m above the plants in order to allow maximum air flow. Also recently, the collection has been repoted from black plastic pots to terracotta coloured plastic pots. Using black plastic pots attracts heat. The soil temperature can be more than 5 degrees higher when using black pots.

Adrian also spent time explaining how to correctly identify some of the species of Saxifraga which I found very useful. He showed me how to look out for particular characteristics in different species. I borrowed a few Saxifraga books from him to read in the evenings. This gave me a better understanding of the history and facts of the genus. I took many notes for future reference. The book on Porophyllum Saxifrages is really great; even just reading the introduction I learnt a lot. As I am partially keen on the silver saxifrages, I have recently been reading the book by Beryl Bland on the subject.

I also got the chance to plant a Saxifraga trough before I finished my placement at Wateperry. I decided on the crevice style, and I started by placing mesh in the bottom of the trough over the holes. I filled the trough with Adrian’s general mix he uses for saxifrages and started to place the rock backfilling with more compost to firm the rocks in place and making sure middle is higher to add more impact and also help with drainage. I went around the frames sourcing plants and got to work planting the trough up and later top dressing with same rock but broken up into various pieces to give it more of a natural look. I always love making troughs and look forward seeing the plants grow on my future visits.

It has been a great month as the AGS Trainee, learning lots as always and meeting yet more new and enthusiastic plant-people on my travels. With a better knowledge of the genus Saxifraga, I am now becoming even more keen on this particular genus and I want to learn even more.