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We effectively treat sedum as a horticultural crop that needs to be harvested, planted and professionally managed to achieve a top quality product, ready for installation on a roof, which will last for many years if properly maintained.
Our process starts with mixing our own compost to make sure that we have complete control over the quality of our inputs. A minimum of 50% of the compost is an inert lightweight mineral material typically derived from power station waste. Other super lightweight materials are also used when requested by customers. Other ingredients include coir (coconut husk waste) and PAS 100 green manure, which we re-process to ensure all weed seeds are killed.
As the green manure breaks down, it releases nitrogen which is locked up by the coir, and slowly released to the plants over a number of years as it breaks down. This interaction between coir and PAS and nutrient availability gives long term feeding to the plant, and allows us to reduce the artificial fertiliser needed to very low levels, without impairing plant quality. Sedum is very responsive to fertilisers; too much applied at the wrong time will make the plants soft and unable to cope with the harsh conditions on the roof. Adding slow release fertilisers will only give a maximum of 6 months nutrient availability.
We work closely with Wallbarn to help refine the green roof and M-Tray® concept to develop peat-free and ultra-lightweight substrates that are suitable for a wide range of commercial and domestic installations.
This ensures each tray is evenly filled to the optimum level, just above the top of the tray to allow for shrinkage.
Trays are seeded using a hydro-seeding system which gives a very even distribution of the very tiny sedum seed.
Seed will germinate about 7-10 days after sowing, and is very vulnerable at these early stages, so we irrigate several times a day to keep the surface of the compost moist. Once established, we start a fertigation programme to feed the seedlings with every watering at a very low level of feed. This gives us very rapid growth with minimal risk of fertiliser and water run-off.
During the growing season, some weeds inevitably appear and these have to be removed by hand as there are no suitable herbicides.
Using this method, trays planted and seeded in the Spring can be ready for harvest that Autumn, but can also stay in good condition on the nursery for up to 2 years.
The quality of the products are also dependent on the species sown. We use a specialist green roof mix from Jelitto seeds which includes the following 13 sedum species.
At any one time of the year, one or two species will dominate and die back and be replaced by other species as the seasons progress. In different climatic conditions (drought/heat) one group of species will become prominent over others. We find this combination gives us the best chance of a very extensive long flowering period on sustainable roofs in a huge range of circumstances, ranging from plants that are grown in water to those that do not receive any.
Our sedum M-Trays® are only harvested when roots are fully established into the trays and there is sufficient tough top growth to survive packing and transportation. We have developed self-propelled harvesting machinery to speed up the harvesting process, allowing us to respond rapidly to customer orders and to cope with the very high demands from major installations, where speed is important to maintain the quality of the trays. We regularly cope with the harvesting of up to a thousand trays per day. Trays are stacked onto pallets, securely strapped and over-wrapped to allow them to be lifted directly onto the roof by forklift or crane for installation.
See the whole Seed to Sedum process by clicking on the link. You can also find a lot more information about sedum green roofs and how to incorporate a sustainable green roof into your building design by visiting Wallbarn.
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Butterflies, hoverflies, solitary bees and birds all love our sedum and wildflowers.