Working our way down from the top storey, the final two layers of a forest garden are the herbaceous perennial layer and the root zone, the rhizosphere, plus the climbers.
I do not plant many roots mainly because I do not want to dig up much of my forest garden. I prefer it to be a semi wild zone that I wander through and harvest at above ground level. Martin Crawford at the Agroforestry Research Trust suggests you can grow useful roots like liquorice (Glycyrrhiza spp) and the barberries (Berberis spp) whose roots provide a good dye and medicinal products. The tincture of the latter can be used as a powerful cleansing tonic. I grow horseradish, a feisty root enjoyed in a creamy sauce with roast beef and in Japanese cookery.
Perhaps the herbaceous perennials are easier to identify and plant. The most popular are herbs that provide ground cover layer by self-seeding or spreading. These may include comfreys (Symphytum spp), lemon balm (Melissa officinalis), mints (Mentha spp), sage (Salvia officinalis), and tansy (Tanacetum vulgare). I personally wouldn’t plant Tansy in my garden. It self seeds madly all over my garden and unlike lemon balm I can’t pick the leaves as a herbal tea. The others spread nicely and crowd out potential weeds.
The comfreys are a different matter. I plant them beneath the fruit trees. They form a circle around the trunks and outgrow any weeds. Their powerful roots are dynamic accumulators, drawing valuable minerals up from the subsoil. When they flower I cut them down with a hand scythe. The leaves fertilise the trees, very useful when the fruits are setting. Comfrey is the best living mulch I know. I also find it useful as a natural barrier between the veggie patch and the wildflower meadow, preventing flowers and grasses from seeding too much into the wood chip paths.
Other ground cover plants that can be used are any medicinal or useful plants that grow well in your soil. My garden loves pink purslane, a pretty little herb that has an edible leaf that has an earthy taste of peas. The Romans brought it to Britain but most people have forgotten that it is a useful edible. It also does well in shady spots. Other plants popular amongst permaculturists are the carpeting brambles (e.g. Rubus calycinoides and R. tricolor). I have tried to establish these on my calcareous soil, but the glossy leaves and vigorous bushes I might find in other soil types have so far struggled. The fruits are not that tasty either, but they do look good.
What has worked for me are the perennial kales. I was given a few cuttings from friends in Wales. All you have to do is simply root them in a pot of soil and plant out when established. They love to grow! They make a tasty green when all else is bitten by frost. Be warned though pigeons love them and will strip them bare, though so far they have always recovered. There are many variations of the perennial kale theme. I have just acquired an asparagus kale from Rod Everett at the Middlewood Trust near the Lake District. It grows prolifically and self seeds very successfully on Rod’s clay soil. I hope it will like our drier conditions.
Lastly, there are climbers. In a sunny site, you can grow grapes and kiwis up trees. I have a self fertile kiwi but it is growing on an existing structure: the kid’s now defunct swing (until at least the grandchildren come along one day!).
What I also grow a hybrid bramble that has succulent fruit twice the size of a hedgerow blackberry. As with all blackberries, you have to be careful as it loves to drop its canes to the ground and root wherever possible. I also grow other less vigorous hybrid berries up the fruit trees, like Oregon grape, dewberry, sunberry and tayberry. I love tayberries particularly. They are delicious, like large juicy raspberries, and require virtually no work. You just have to prune out the dead wood after it has fruited.
Lastly, as I garden on chalk the chalk downland species thrive: marjoram, knapweed, scabious, cranesbill and campions, and many others, all self seed and bring a riot of flowers from spring until September, just when I want the beneficial insects to enjoy the garden; to pollinate the fruit flowers and eat any pests on the fruit trees and in the veggie garden. The insects attract bats too which helpfully eat codling moths, the bane of fruit growers. Since the garden has become established (in the early days is was different, but that’s a story for another time) I have never had a problem with any pests on the fruit trees and my system is entirely organic, unsprayed and semi wild. I am sure this is because I am working with nature in true permaculture fashion and have established a high level of biodiversity in the garden.
I will be writing about some of the ways you can do this too in future blogs.
My advice on establishing the ground layer is not to be too ambitious. Make life easier for yourself by mulching out a small areas and planting them up densely. Do not bite off more than you can chew!
If you have lots of bare soil sow your native wildflowers that love your soil type and climate. You can always mulch them out later if you wish and exchange them for more medicinal and edible plants. If you forest garden this way, you will establish good ground cover first and a habitat for friendly insects and reptiles who will control the pests.
Next: Using the principles of forest gardening in a small, urban space.