Gardener’s Notebook by Joshua Burman Thayer
In 2003, researchers at the University of California, Berkeley, reported that a simple brick wall can shift the air temperature adjacent to the wall by over 13°F compared to the surrounding area. Walls, berms, pergolas, and other human designs can significantly increase or decrease temperature in various parts of your garden, and plants, too, create microclimates around themselves by blocking wind, absorbing sunlight, and creating cool patches of shadow.
Modest shifts in temperature of just a few degrees can make the difference between a hard winter frost and one that settles just above the threshold for damage, thereby saving frost-sensitive plants from freezing. In summer, a few degrees can be the difference between your heirloom tomatoes ripening or not. Other plants may be wind sensitive, and hedgerows can be key to their success.
ORANGE Plants identified as full-sun options are often evergreen, round, full, and tough, qualities that help them take the brunt of full sun. Here in the orange zone, you can see how plant communities can be grouped by their light needs.
Habitat Plants: manzanita, ceanothus, lavender, sage, deer grass.
Edible Plants: citrus, pomegranate, olive, carob.
GOLD These plants can take a good deal of hot sun, but you can give them a bit of a break by planting them here, where they do not receive direct sun until midday.
Habitat Plants: yarrow, elderberry, penstemon, fescue.
Edible Plants: fig, persimmon, plum, pluot, apple.
LIGHT GREEN The cool eastern side of the house is a zone with plenty of gentle morning light that comes prior to midday heat. In the hot afternoon, these plants benefit from the shade cast by the house.
Habitat Plants: currant, wax myrtle, mahonia spp, azalea, rhododendron.
Edible Plants: blueberry, herbs, raspberry, lettuce, apple, pear, cherry, gooseberry.
DARK GREEN The northern edge of the property gets good light in summer and moves into cool shade in winter.
Habitat Plants: redbud, oak, juniper, magnolia, rhododendron, azalea.
Edible Plants: avocado, apple, pear, cherry, grape, kiwi.
BLUE This zone has the least direct sun of any shown in this exercise; it is the place that stays the wettest and coolest on the property, so this is where you’ll group your full-shade plants.
Habitat Plants: ferns, orchids, succulents, mahonia, sedge.
Edible plants: greens, culinary herbs, moringa, currant.
We can use south-facing walls to hold and radiate the heat of the sun. Masonry, stones, boulders, and similar materials that have thermal mass can heat up significantly when exposed to the sun. They store the sun’s heat and radiate it back out as the ambient temperature cools. A south-facing wall can be much hotter than a nearby open meadow. This holds true through each season. In the cooler parts of California, a heat-absorbing wall can be an amazing asset, promoting growth in hot-climate plants like tangerine, or to keep a Haas avocado from freezing in a cold snap. Walls create a more tropical condition than otherwise would exist in the location.
Planting in Microclimates
The eastern edge of the garden is where the sun rises, so placing dense evergreens or a hedgerow on the eastern margin would be disadvantageous as it would delay the arrival of morning sunlight. By planting tall deciduous trees such as apple, pear, plum, or fig, on the eastern edge of your property, you avoid blocking the preciously scarce winter light. The northern edges of your front and back yards are the best places to site your largest trees, visual screening, or wind blocks, since they can grow densely without over-shading the other specimens in your garden. These plantings can act as living walls to protect and buffer gardens to their south. Ideal candidates for the northern edge are conifers, avocado, nut trees, and hedge trees.
The western flank of your property receives the hot light of afternoon. Those hours provide the vital energy needed for optimal fruit production. Whether you are growing tomatoes, peppers, peaches, or plums, the afternoon heat and light exposure are paramount to a large fruit set. This is why you want to avoid adding a vertical element that will loom too large as it grows on your garden’s western flank.
Dry Shade Perennials for Food Production
If you have dry conditions and areas of mixed light and shade, such as in the under story of oak woods or on the fringe of pinewoods, you can plant the following food-producing species, which need only four to five hours of daylight to reach full production potential:
- Elderberry (Sambucus mexicana)
- Gooseberry (Ribes uvacrista)
- Currant (Ribes nigrum)
- Blueberry (Vaccinium spp)
- Boysenberry (Rubus ursinus × r. idaeus)
- Mulberry (Morus alba)
- Raspberry (Rubus idaeobatus)
- Blackberry (Rubus spp): ‘navajo’, ‘ollalie’
Joshua Burman Thayer’s Gardener’s Notebook is filled with gardening advice for every season. Visit the whole collection of articles here.
Get expert help with your garden from Joshua Burman Thayer at 510.332.2809. Learn more about food forests and permaculture landscape design at nativesungardens.com and from Joshua Burman Thayer’s new book, Food Forests for First Timers.