How to Select a Tree Planting Site
The first question to ask: can you grow fruit trees where you live? What can grow where is largely dictated by climate and weather. Some people use the two words interchangeably, but climate is the way the atmosphere behaves—the weather conditions over a long time period (30 years). Climate does change; for instance, in 2012, the US Department of Agriculture (USDA) added 5°F to the low temperature readings for all of its climate zones. When we talk about weather, it’s more about the specific conditions (rain, fog, temperatures, wind, and sun) over a short period of time: today, the 3-to 5-day forecast, seasonal forecasts.
The USDA assigns each type of fruit a cold hardiness zone, which indicates where in the United States that fruit can be grown. These hardiness zones account for the average low temperatures for different areas. You can figure out what USDA hardiness zone you live in on the USDA website.
While USDA zones won’t tell you all you need to know about the ability of a particular variety of fruit to thrive in your location, they will at least help you set the parameters for what you can grow in general.
Hardiness zones are pretty cut-and-dried: below X temperature, the tree will die. But heat is also a factor in a tree’s growth. Heat triggers faster, greater growth and fruit development and high sugar content.
Although heat is desirable, too much can be harmful. A sustained series of days with temps higher than 92°F–95°F will be problematic. Particularly in mid- to late summer, a heat wave in excess of 4–5 days will cause the tree to need more water and also can cause heat stress, which makes trees more susceptible to pests. Too much sunlight can sunburn leaves, fruit, and branches. That doesn’t mean you can’t grow fruit trees; overall, the deleterious effects of heat are more subtle than those of cold. (One of the typical ways people deal with the problem of heat is to allow the tree to develop a thick canopy. This offers more shade for the fruit and branches and can minimize heat damage. Another trick of the trade is to sprinkle the trees with water overhead on mornings when it’s expected to be hotter than the mid-90s. The resulting evaporative cooling effect can lower the tree canopy’s temperature by 8°F –10°F.)
Wherever you live, you should find out what has been grown successfully in your area—recently, as well as historically. If something grows well in your neighborhood or county, you can likely make it grow well for you, too. The best way to understand what grows in any region is to talk to locals (home gardeners, orchardists, homesteaders). Walk around and look at what your neighbors are growing. Search online for nearby land grant universities, which have mandates to educate the public about agriculture. These are usually state universities, and most have Cooperative Extension Systems (CES) that put out excellent websites, workshops, or talks accessible to the public. As biologist Roger Payne wrote in his book Among the Whales: “Any observant local knows more than any visiting scientist. Always, no exceptions.” When it comes to growing things, any well-informed, tuned-in local knows more, in a more nuanced manner, than most or even any so-called outside expert. As you ask around, don’t forget that land values can affect crops, too. For example, an area that used to have apple orchards may now be full of vineyards, strawberries, or higher-dollar crops (or, perhaps, summer homes for the wealthy). But chances are, apples will still grow well there.
To produce fruit, deciduous fruit trees need bountiful sunshine, but they also need sufficient cold weather. When a tree is dormant in wintertime, it requires a certain number of hours when the temperature is between
32°F and 45°F in order to enforce a period of rest, before the tree breaks dormancy and resumes growing in the spring. Orchardists call these chill hours. During dormancy, a tree will not resume growth until it has received its required chill hours. This adaptive strategy gives trees the ability to resist outside environmental cues to grow during warm winters or “false thaws,” and to wait until favorable growth conditions occur in spring. It’s important that the varieties you intend to grow match the chill hours in your area.
Chill requirements are more quickly and easily achieved with a continuous rather than alternating chill; temperatures greater than 60°F will undo some of the chill hours a tree has achieved.
Chill Hours in Different Regions
The chill needs of a deciduous tree usually reflect the climate of that fruit’s origins. For example, apples are originally from Kazakhstan and Uzbekistan, plums came from northern Europe, and peaches, nectarines, and apricots hail from northwest China. Their required chill hours correspond to the climate of those regions. Pick varieties that have about the same chill hour requirements you are likely to get in your area. Choose wisely.
Generally, different growing regions have different predictable chill hours. Note that I said “predictable” chill hours. Who knows what the future holds? The Central Valley of California produces about 90 percent of the nation’s deciduous fruits. If average temps in the Central Valley rise by 1°F–3°F, deciduous fruit tree production will become nearly impossible. As growers, we must constantly notice and adapt to the changing climate around us. Adapt or perish, as they say . . .
Similarly, different fruit species have different chill requirements. (Citrus are not categorized using chill hours, as they are a “tropical” fruit.) The chart that follows shows the general ranges for different species. In the next chapter, we’ll get into the chill hour needs of individual varieties.
To find your area’s chill hours, consult your local authorities—neighbors, nursery workers, community garden members, etc.—or do a quick internet search—for example, sites like getchill.net allow you to search for your chill hours by zip code.
In addition to the macrolevel climate, you need to have an understanding of the minute weather patterns in your specific yard or piece of land. This is where you become your own best expert. Embark on a project of regularly observing your prospective site. I recommend setting up a small homemade weather station. It’s easy and inexpensive, and it can be good nerdy fun. Go down to the hardware store and grab a high-low outdoor thermometer (about $40), a small rain gauge ($5 or so), a simple, cheap wind vane, and a blank journal or notebook. Observe and record what’s happening.
Keep track of the high, low, and average temperatures in your orchard. This will help you understand your cold and heat parameters. Note how many hours of direct sunlight your site gets. Are there prevailing winds? Wind can be hard on plants. Exposed sites may need extra attention or even windbreaks—perhaps a hedge. Be aware of the date of your first and last frosts of the year, especially the last frost in springtime; these dates define your growing season. Frost during the bloom period (early spring for most deciduous trees) will damage your blooms—no crop. And if you live in an area with late spring frosts, you’ll want to stay away from varieties that bloom and ripen early in the season. At the fall end of the growing season, it’s less of an iron curtain, but a significant frost can still injure fruit and get you in trouble.
Collecting and tracking this kind of weather data will help you lock in to where you live, in your own yard and beyond, and get in touch with it. This will allow you to figure out not only where to put your trees, but how best to tend them once they’re planted.
From the time they bloom through harvest, fruit trees require a minimum of 6–8 hours per day of full sunlight. Period. And 8–10 would be better. Why so much sunlight? No light, no photosynthesis.
Sunlight also generates heat, which is important during the bloom period and encourages insect activity and pollen viability (flow).
Go outside and look around. Pace about. Track the sun—morning, noon, and late in the day. Track it at the spring and fall equinoxes and at both summer and winter solstices. This will take time—a year. But fortunately in the age we inhabit, there are tools and aids to help you do this faster. Try websites like Find My Shadow, SunCalc, and Sollumis. The University of Oregon has a cool sun chart feature on its Solar Radiation Monitoring Laboratory page. Or try the apps Sun Surveyor and Sun Seeker. All these kind folks will do the math for you and map the sun’s path across your property.
Sun is life. Make sure your chosen site has enough.
The Lay of the Land
In analyzing the topography of the spot where you plan to grow, the two main considerations are flat ground versus sloping ground.
What is the key advantage of flat ground? Well, it’s flat. That is, it’s much easier to work. It is also less erosion prone. Often flat ground will have deeper, darker, more fertile soil, especially if it is at the base of a slope or is river bottomland (and it’s potentially wind protected).
And the cons? Well, your area of flat ground could be a frost pocket, especially if it’s on a valley floor. Cold air is heavier than warm air, and like water it drains downslope and accumulates at the bottom. Such topography is to be avoided. Frost during the bloom period will cause poor fruit set or even lead to being “frosted out”—no crop. Flat ground may also have drainage issues. As an old farmer once joked to me, this makes it great for growing hay; trees, not so much.
Sloping ground is your other option. With sloped sites, the slope and direction of the soil surface create a microclimate and subtle, even significant differences of soil and air temperatures. The direction of the slope is referred to as aspect.
A gentle south-facing slope (less than 4–8 degrees) is probably the most favorable of sites if you live in the Northern Hemisphere. (In the Southern Hemisphere, it is the reverse: north facing is favorable.) South-facing slopes, along with southeast-and southwest-facing slopes, offer a warmer microclimate and are less prone to frosts.
South-facing slopes allow cold air to drain downslope, and blossoms and fruit are more protected. South slopes warm more quickly in spring, are warmer in summer, and stay warmer longer in fall. And because they’re slopes, they usually feature good soil drainage. Drawbacks of the south-facing slope include potential wind exposure and the possibility of thinner, nutrient-poor soil.
A caveat about the legendarily good south-facing slopes: some say they are amiable; others call them sacred. Certainly they’re advantageous. But in northern regions, the warmth of a south slope can force bloom too early, making flowers and fruit subject to potential early frost. Also be wary of windy conditions at the top of slopes. Wind is generally hard on plant growth. It increases evapotranspiration (water loss) from both the soil and the plant. Plants that are constantly buffeted by wind put more energy and reserves into creating thicker, more sturdy stems and leaves. They do this at the expense of vigorous shoot growth. So if you’re bemoaning the lack of a south-facing slope on your land, don’t be too taken aback. You can still grow fruit trees.
Southeast and southwest slopes offer similar heat advantages to south-facing slopes, but to a lesser degree. Southeast slopes offer both warmth and quicker recovery from nighttime frosts as well as quick-drying foliage after night rains and even dew. Quick drying of foliage minimizes leaf fungal diseases. Southwest slopes stay warmer longer into the day as well as longer into the fall.
North-facing slopes offer the coolest of all directional microclimates. The more oblique angle at which the sun strikes the ground causes the sun’s rays to be spread over a greater area, and thus they don’t transfer as much heat energy. Simply put, north slopes are cooler overall and delay the break from dormancy. This can be a good thing for some early-blooming varieties in areas that have late spring frosts and rains, as it will delay the bloom until after the damaging weather events. The soil on north slopes can be deeper, often has higher organic matter percentage than on south slopes, and retains soil moisture longer. A north slope may be a boon in extremely hot summer areas, as sites can have too much heat (maybe not too much sun, but too much heat). If you’re planting on a north slope, you’ll have a shorter growing season. But it’s doable.
More from Fruit Trees for Every Garden
Reprinted from Fruit Trees for Every Garden. Copyright © 2019 by Orin Martin and Manjula Martin. Photographs copyright © 2019 by Liz Birnbaum. Etchings and illustrations copyright © 2019 by Stephanie Zeiler Martin. Published by Ten Speed Press, an imprint of Penguin Random House LLC.
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