Shifting 20 tonnes of bracken mulch will reap rewards in the year to come
A 20-tonne heap of organic ‘stuff’ has appeared under the black walnut, Juglans nigra, in the Woodland Garden. The size of this pile of composted bracken could seem intimidating, but to us lucky ones who have to spread it on the beds, it’s an annual task that pays big dividends.
Bracken mulch to be spread over the woodland garden beds
In nature, autumn delivers a deep mulch of leaves to the woody and herbaceous plants growing on the forest floor. The fallen leaves insulate the ground and gradually decompose. Soil organisms work them into the ground where they deliver micro-nutrients and act as fantastic soil conditioners. It’s a perfect circle.
But here at Kew, we have to pick up the fallen leaves – to protect our turf and keep the paths accessible (and to prevent homicidal impulses from the Rock Garden team, who rightly object to the arrival of leaves on their beautifully kept beds).
So to make up for robbing the Woodland Garden of its leaves, in mid-November we mulch! Kew produces a ‘soft mulch’ using composted plant material from on site mixed with horse manure, but this has quite a high pH and high nitrogen levels, neither of which are suitable for the majority of woodlanders.
Why bracken mulch?
Bracken mulch (Pteridium aquilinum, composted for two years) is low in nitrogen and has a neutral-to-acid pH. It is a good soil conditioner too, increasing the soil’s ability to hold water and nutrients (Kew has a very free-draining soil, so we have to work hard to keep it in good health).
How and when
We mulch in November when the soil still has some warmth from the past season and before the spring-flowering bulbs start to emerge. We cut back the herbaceous plants, and weed and remove the majority of the leaves on the bed so that we can see exactly where to put the mulch.
Using wooden boardwalks to drive our loaded barrows onto the beds, we spread the bracken mulch in a layer 6-8 cm thick. We take care not to smother rosettes – like Meconopsis and Primula species, and we leave a good bare circle around the base of smaller shrubs (it is easy to over-mulch woody plants, effectively choking them).
It’s rewarding work, because the beds look beautiful with their rich, red-brown duvet... at least for a few hours, before the oaks chuck down another layer of crispy golden leaves. These we collect and put aside to make leaf mould (but that’s a story for a future blog).
And even now, plants are stirring under ground. The Trillium buds are just visible, gathering pace for spring which, despite the evidence to the contrary, is just around the corner.
- Katie -
Several people contribute to the Alpine and Rock Garden Team blog. Richard Wilford is the Collections Manager in the Hardy Display Section at Kew. His responsibilities include all the areas where alpines are grown at Kew Gardens. The three team leaders, Joanne Everson, Graham Walters and Katie Price, each have their own particular parts of the Gardens to look after. Between them, these four experts have over 55 years experience of growing alpines.
Alpines at Kew Gardens are not only grown to create colourful and informative displays, they also play an important role in the research Kew carries out around plant naming, classification, biodiversity and conservation.
Mountains are found on every continent and each range has its own unique alpine flora, but these plants are under threat from climate change. As temperatures rise, alpines are forced higher and will eventually have nowhere to go. The alpine collections at Kew are studied to help us all understand the mountain flora better and make informed decisions about protecting its future.
"Probably the most beautiful glasshouse in the world is the Davies Alpine House at the Royal Botanic Gardens Kew", John Hoyland, Gardens Illustrated, April 2011
Richard Wilford has written a book on alpines, 'Alpines from Mountain to Garden', published by Kew Publishing. You can buy it in the Kew shops or from Kewbooks.com.
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