Layers of a Permaculture Food Forest Part 4: Understory and Canopy Trees

In our exploration of temperate food forest layers, we’ve been taking a closer look at each of the 7 layers; what we can plant there and how to design each layer for optimum results across the whole garden. 

So far, we’ve looked at the root layer of a food forest, groundcovers and the herbaceous layer, and shrubs.

In this article, we’ll be looking at tree crops, big and small… the roles they play and how we can incorporate them within the rest of the ecosystem that makes up the forest garden.

The Two Categories of the Tree Layer in a Food Forest

1. The understory – Smaller trees and larger shrubs such as apples, plums, and hazels up to around 6 meters (20ft).
2. The canopy layer – Taller trees like chestnuts, pine nuts, and alders that rise above the understory.

The Tree Layers Perform Multiple Functions in the Forest Garden

• Providing the right quantity of shade and shelter for the rest of the system to thrive.
• Drawing up water and minerals from deep in the subsoil – an integral part of various bio-cycles.
• Sequestering large volumes of carbon from the atmosphere, accumulating biomass.
• Depositing large volumes of carbon back down to the soil surface via annual leaf fall, building soil.
• Offering an invaluable habitat and sustenance for countless birds, mammals, insects, and micro-fauna.
• Producing edible, medicinal, and otherwise useful crops for the gardener!

Let’s take a look at what we can grow in each of the two layers in more detail.

The Understory Layer of a Food Forest

Sweetheart Cherry Tree from Nature Hills Nursery, Inc. 

Fruits 

Crops like apples, plums, cherries, pears, peaches, apricots, and figs are fruit tree species that most people are likely to know, but there are plenty more exciting possibilities for the temperate forest garden understory too…

Cornelian Cherry (Cornus mas)

Cornelian Cherry (Cornus mas) is a fruit that’s well known to South-Eastern Europe, yet hasn’t found much favor in the rest of the world yet. I wonder why because this is one of my very favorite of all berries.

When fully ripe, they really explode with a cocktail of flavors, including very rich cherry tones – hence the name. Also a very pretty shrub, with bright yellow flowers in late winter offering the bees early sustenance.

Mulberry

Red Mulberry Tree from Nature Hills Nursery, Inc. 

Mulberries are another of my favorite fruits that deserve to be planted far more widely.

Although the dried fruit is now becoming more popular on the health-food scene, the pleasure of eating the fresh berries is one reserved solely for the gardener – they’re so delicate that they can’t even make it to the market without “melting”!

Blue Sausage Tree (Decaisnea fargesii)

The Blue Sausage Tree (Decaisnea fargesii) is a very unusual sounding, unusual looking tree from the Himalayas and China. Its nearest well-known relative would be that of the Akebia family. 

I find its other name “Blue Bean” a bit misleading since its seeds are not edible – but the slimy flesh that surrounds them is indeed sweet and pleasant! Just as long as no one around you minds the onslaught of seeds fired from your mouth after each bite! 

Hawthorn (Crataegus sp.)

Another family of trees that can be included in the understorey is Hawthorn (Crataegus sp.) – several of which produce cherry-sized fruits that taste more like sweet apple pulp.

Hawthorns tend to be tough, drought-resistant plants that also serve up an annual feast for pollinators.

Medlar (Mespilus germanica)

Medlars, which are closely related to Hawthorns and pears, are pretty, weeping trees that produce fruit that taste like something between a date, dried banana, and baked apple.

Very yummy, as long as you don’t mind the tough skin and spitting out the rock-hard seeds!

Loquat

Gold Nugget Loquat from Nature Hills Nursery, Inc. 

Lastly, and also known as “Japanese Medlars”, Loquats are a great understory fruit for warm-temperate climates.

When I was in Spain years ago, I feasted upon kilos of these straight from the trees – their sweet-tart juiciness had me totally hooked! The leaves can also be brewed into a tea known in Japan as “biwa-cha”. 

Nuts in the Understory Layer

Hazelnut from Nature Hills Nursery, Inc. 

Almonds and Hazelnuts are the two most obvious nut crops to grow in the understorey.

Whilst Hazels are very at home growing under the shadow of taller trees, Almonds really need a full day of sun to give their best crops. Look out for Almond cultivars that are resistant to “Peach Leaf Curl” disease, to which they are susceptible.

Spice Crops

One of the most exciting things about forest gardens is the sheer variety of crops one can grow.

Hardy Pepper (Zanthoxylum sp)

If growing your own spices in a temperate climate hadn’t occurred to you, you might be intrigued to learn about the Zanthoxylum family, or hardy pepper trees.

Species include Szechuan Pepper, Japanese Pepper, and Nepalese Pepper and produce some of the most aromatic fruits and leaves of all plants in the world. 

Bay Tree

Bay Laurel from Nature Hills Nursery, Inc. 

The Bay Tree or Bay Laurel (Lauris nobilis) is a better-known spice tree for its highly scented leaves. Its evergreen nature also makes it useful for shelter during the winter months. 

The Canopy Layer of the Food Forest Garden

Smaller forest gardens may not require the presence of large trees to complete the final 7th layer. But, for larger plots, the canopy layer adds an extra dimension that gives the garden a much more “foresty” kind of feel.

Let’s take a look at some of the taller trees that can be planted there.

Nuts

Of the taller trees that are edible in the forest garden, most of them are nuts.

Nut crops are among the most exciting in the forest garden for me, as they can really deliver the bulk quantities of carbohydrates, proteins, and fats that would otherwise be produced by far more intrusive methods of farming. 

Here are some of the species best suited to a temperate forest garden.

Sweet Chestnut (Castanea sativa)

Sweet Chestnuts are perhaps my favorite nut crop of all, giving huge yields of a nut that is similar in nutritional value to cereal crops. They can also be used in much the same way – processed into flour for baking bread, pies, and cakes… 

With comparable yields, why couldn’t we be growing them instead of fields of wheat? 

Well, we could! And it would save enormous resources too.

Walnut

Manregion English Walnut Tree from Nature Hills Nursery, Inc. 

Walnuts are more typical of a nut in their nutritional makeup – being very high in fats rather than carbohydrates. They tend to do best in warm, dry climates, but some recent selections are now cropping well in Northern Europe too.

There are also various relatives of the walnut that can be cultivated for nut production.

Black Walnuts (Juglans nigra), Butternuts (Juglans cinerea), and Heartnuts (Juglans ailantifolia) are all being trialed in various parts of the world, although they often still have rather tough shells and less meat inside than the classic walnut.

Diversity is imperative though and with a little more breeding work, these species could add much-needed variety to the forest garden nut menu.

A slight drawback of growing any kind of walnut is the chemical Juglone which they excrete into neighbouring soil, inhibiting the growth of nearby plants. Look out for companions that are more tolerant of this if you wish to grow walnuts in your forest garden.

Pine Nut

Pine Nuts are actually harvested from several different species of pine tree which produce especially large cones and kernels that are sizeable enough to be worth extracting.

They generally do best in areas of cold winters and warm, dry summers, and several trees are needed to ensure good pollination. 

Oak

All acorns are in fact inedible!

They just require us to rinse out bitter tannins before we can turn them into something useful.

A few species with lower tannins can even be roasted like chestnuts and eaten directly. Acorn bread was a staple of the native Californians and acorns are still eaten regularly in Korea. There are many great recipes to try!

Monkey Puzzle (Araucaria)

Monkey Puzzle (Araucaria) is another nut that is still used in bulk by the indigenous Mapuche people of Chile, who refer to the tree as their “extended family”.

I was very impressed trying the nuts of this tree, which fall from huge, football-sized cones. Each nut is up to 5cm (2″) long and to me tasted a bit like a peanut!

Ginkgo biloba

Ginkgo biloba is better known in the west as an ornamental or medicinal tree, yet the seeds inside the disgusting smelling fruits are, in fact, very good to eat!

In China and Japan they make popular snacks, and I think it’s high time the western world caught up to the wonders of Ginkgo nuts, which I’ve seen cropping nicely all over Europe.

Other Canopy Crops

There are a few other ways we can utilize our canopy layer…

Birch and Maple species are well known for their edible, health-giving sap which can be also be processed into syrups and ferments. (Nature Hills Nursery has a beautiful range of canopy trees!)

Nitrogen fixing species such as Alders (Alnus sp.) and Black Locust (Robinia pseudoacacia)  are very useful as “fertility masts” – forming symbiotic relationships with soil bacteria to solidify atmospheric nitrogen – one of the key elements for plant growth. 

Tall trees can also provide much-needed shelter for the garden.

Large windbreaks can be formed with resilient deciduous species like Alders, Birch, and Beech, and dense evergreens such as Spruces and Thujas. 

Valuable Wood Resources

The wood of any tree or shrub species is a naturally valuable resource in itself too!

If the forest garden ever needs substantial pruning or thinning out, this wood can be utilized for all manner of things.

Walnut, oak, and fruit tree wood is highly valued in the carpentry trade, and make important alternatives to tropical hardwoods that are often irresponsibly sourced.

Many species such as oak, beech, and birch are also great for growing mushrooms on!

Shiitake, Oyster, and Lion’s Mane are among the easiest and most delicious varieties of gourmet mushrooms you can grow. True Leaf Market has an awesome range of mushroom plugs and DIY mushroom kits to get you started. 

Wood can also be left to rot on the ground to enrich the soil, or even buried under crops that need extra fertility.

In Hugelkultur, large volumes of wood are buried under vegetable beds to provide hummus over long periods of time.

And let’s not forget firewood.

Fast-growing species like alders and willows can provide large quantities in a relatively short time.

And if you want to save the carbon whilst doing so, you could always build a gasifier – a kind of stove that burns only the gases in the wood, producing almost zero carbon dioxide. It leaves you with a light, black, millennium-long soil conditioner: biochar!

Now there’s a win-win solution…

Designing Your Understory and Canopy Layers

Maximize Sunshine

The most critical of all elements in the temperate forest garden is usually sunlight. 

We must arrange our canopy and understory layers carefully to let in as much sunlight as we can to the fruiting shrubs and perennial vegetation below.

In this way, less is more!

The most common mistake people make when designing their forest gardens is to include too many tree species, which eventually cast too much shade for optimum cropping conditions below. 

Carefully mark the orientation of the sun, and how this changes at different times of the year.

Whilst midsummer sun may reach most parts of the forest garden floor, the fall sun is also very important for later ripening crops. There are some great apps for smartphones to help with this these days!

Researching each species’ sun requirements is an important, time-consuming part of this process, and I’d highly recommend reading some material dedicated to the subject, such as the book suggested at the end of the article. 

Size Matters…

Make sure you know the eventual height and spread of each tree you’ll be planting. 

Although it might be difficult to imagine in the beginning, a sweet chestnut tree could easily exceed 10 meters in width within your lifetime! 

I find a great way of planning the tree layers of the forest garden is to cut out color-coded paper circles to represent the size of each tree, before placing it on a garden plan of matching scale. This way the design can be moved about and swapped around as your ideas develop over time. 

Here is a simple example I created for a Mandala forest garden in Sussex, UK:

Zone Your Trees for Easy Harvesting

Another factor to consider when planning your tree layers is placing trees according to how frequently you’ll be harvesting them.

While many tree crops like winter apples and nuts can be harvested in one or two sessions for storage, others like summer apples and mulberries will give a steady supply of fresh produce over a longer season.

Locate trees that offer regular, fresh produce in places where you will pass often, and those which you only need to harvest annually at the garden’s far reaches. 

Think About Pollination

Most of the tree crops listed above are self-sterile meaning they need at least one compatible partner to pollinate them. 

Fruit trees are normally insect-pollinated and simply need positioning nearby others of the same species that blossom at the same time.

Nut trees on the other hand are mostly wind-pollinated and often need planting in larger groups for good yields – although there are exceptions. Ask your stockist to guide you on pollination if you are in any doubt! 

…and take your time!

With all of this in mind, the canopy and understory are laid out with great care so that all of the elements combine together to produce optimum yields over the whole system.

It can be a long process, but when it’s not rushed it can be brilliant fun, and you’ll be rewarded for every bit of love and care you put into your plan. 

Enjoy Yourself…

Don’t forget that one of the most important yields is your enjoyment – as the gardener!

It’s my wish that the rays of dappled sunlight, gently filtering through the well-crafted layers of trees and shrubs will bring joy to your heart for many years to come.

Martin Crawford’s Creating a Forest Garden is an excellent guide for beginners and advanced gardeners to learn more about the art of forest gardening. Incorporating his 20 years of experience in Devon, UK, I’d highly recommend this book for any prospective forest gardener in a temperate climate.

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Last update on 2021-03-23 / Affiliate links / Images from Amazon Product Advertising API