In the classes I teach, home owners who have become aware of the thousands of possible vegetables, fruits and herbs they could grow, often lament “I just don’t have any more space for that.”
As a possible solution, they usually ask me what will grow in shade, and I usually tell them that many herbs, vegetables where you eat the leaves, and blackberries are the best possibilities. But that brief answer is simplistic.
What I would say if I had time to explain is that, “Permaculturists have a technique called stacking that may help you.” Stacking is useful in situations where you think there isn’t enough land for your goals, and you want to get more out of less.
Permaculture is a design philosophy and methodology. It integrates ancient and modern technologies with an understanding of nature and detailed observation, to guide effective plans for sustainable living. It is taught in 72-hour classes in periods from ten days to a year.
In aged natural forests, there is a tall tree canopy layer fifty feet or more above the earth, with shorter, more shade tolerant trees below them, and even more shade tolerant low-growing bushes, shrubs, herbaceous plants, ferns, and fungus living close to a heavy mulch layer and the earth itself. On the trees, there are often vines such as wild grapes, Virginia creeper, or cross vine.
These forests contain many times the biomass of a similar acre of less layered vegetation such as prairie, most gardens, lawn, or edged walkways. So per square foot they produce much more soil-building plant liter. That in turn, prevents runoff and holds much more moisture for much longer.
The shade canopy acts like a 50 ft. insulation, keeping temperatures cooler, so there is much less evaporation from the surface. The mulch layer also keeps the surface damp even in summer, so the roots, mainly near the surface have a continual supply of moisture to support growth.
The tree layer provides millions of square feet of leaves whose water content keeps them from cooling or heating as fast as the surrounding air. So dew condenses on them, producing more precipitation. The plants then use a high portion of the water collected, and eventually transpire it back into the air.
Worldwide, 60% of all rainfall is from plant transpiration. Inland the percentages are higher and near the ocean lower. Thus Galveston rain is mainly from the ocean, but Houston tap water, coming as it does from the Trinity, is mainly of botanical origin. So natural forests and woody landscapes are not just the lungs of the planet, but also its blood supply! Native understory plants like ferns, beautyberry, scarlet buckeye, and parsley hawthorn do a lot of good for us.
Another natural design found in forests is the guild. This is an assemblage of plants, animals and other items that provide benefits for each other, thus making it possible for more to live in a smaller space. For example, a blackberry thicket might protect a young tree from deer, and later, the older tree might provide mulch and bird droppings to help the blackberry grow.
A third natural design we can use in our gardens is ecological succession. If a forest is partially cleared by an avalanche, disease, or fire, new sun-loving plants occupy the cleared ground quickly. These provide shade and organic matter to nurse small shrubs and trees, and these in turn help even taller trees to emerge.
Thus without any human help, nature has sustained itself here for millions of years because it has a very efficient system for growing plants close together. But we too can use natural and other designs to stack our yards.
Stacking is related to understory, guild and succession, but embellishes these designs for the purposes of gardening. Vertical stacking is an effort to plant several useful plants of different heights in the same space.
In horizontal stacking, by contrast, several useful plants are planted adjacent to each other in order to benefit each other This is done using the guild concept—beneficial assemblages promote higher production.
Temporal stacking places plants near each other that will enjoy most of their growth during different seasons, or years.
In my own garden, I use stacking to squeeze more and more production out of my house-lot. I grow several sweet varieties of hybrid muscadine grapes on a wire between ten-foot U-stakes. Vertically stacked below these are domestic blackberries tied to the stakes. And below them on the ground suppressing weeds is our favorite summer green– sweet potato spinach. These three plants all do well in sun, but two are still productive in partial shade, so we can make use of this to vertically stack.
Horizontal stacking uses mutually beneficial qualities of plants such as the different micro-climates created by different plant heights. In winter, the warmest part of my yard is on the southwest side of my house in a sunny space between two tall grapefruit trees. That’s where I have my tropical plants—papayas, guavas, pentas, tropical passionfruit and two coffee plants. There is no room for more grapefruit but plenty for these heat loving smaller plants.
The typical temporal stacking is to understory a preferred tree that when it gets big enough, can replace what was above it. I am growing a very hardy experimental avocado under a poor quality citrus. But a less obvious example is the strawberry patch. Strawberries need winter sun to produce and summer shade to be perennial. The solution is to leave two-foot wide spaces in the strawberry patch so that summer vegetable plants such as basil, peppers and okra can be planted where they will shade the strawberries all summer.
Stacking is just one of more than two-dozen sustainable land design concepts to be taught in permaculture classes through Urban Harvest at http://www.urbanharvest.org