Microclimate comes into play with spring frost hazard. A difference of a few degrees of temperature can spell the difference between a bountiful harvest and just a few, or no, fruits. Hence the importance of a microclimate.
Illustration Courtesy The Taunton Press
Pick luscious fruit right from your own sunny balcony, suburban lot or orchard with the help of the ultimate fruit growing guide, Grow Fruit Naturally (The Taunton Press, 2012) by Lee Reich. Grow the best-tasting apples, blueberries and more with natural practices ranging from cross-pollination to irrigation methods. An encyclopedic listing of fruits presents comprehensive information on individual fruit care and needs. Learn the basic requirements for creating a fruit garden in this excerpt taken from Chapter 1, “Planning Your Fruit Garden.”
You can purchase this book from the MOTHER EARTH NEWS store: Grow Fruit Naturally.
The weather is springlike, and fruit plants in color-splashed mail-order catalogs and at local nurseries tempt you with possibilities of luscious harvests for years to come. You pay your money, you dig holes, and you plant, but will you realize your tasty dream? Yes, if you plan before planting!
What requires attention in planning is sunlight, climate (including temperatures and rainfall), pollination needs, plant spacing, and how much of particular kinds of fruits you’d like to harvest. The most straightforward approach is to plan your fruits around the existing conditions in your yard and the varieties of plants that can flourish there.
One of the most important considerations in determining where to plant and what to grow is sunlight, which you can influence to some degree.
Most fruit plants need full sunlight, which means 6 hours or more of unobstructed sunlight each day from spring through autumn. If your yard lacks this much sunlight, consider your options for gaining more light. For example, are there trees you can cut down or back? Or go ahead and plant, realizing that there will be some sacrifice in yield and your plants will be more susceptible to diseases. Another alternative is to plant fruits such as gooseberries or currants, which thrive in shade.
Surprisingly, perfect soil is not all that important in site selection. Fruit plants do thrive best in soil to their liking, which is especially important with naturally grown fruits that are going to be rich in nutrients and able to naturally resist pests. At the scale of home-grown fruit, though, you can feasibly, if necessary, modify the soil right at the planting site to suit the needs of a specific tree, bush, or vine. That is, unless you are trying to grow fruits on such “terra-ble” soils (for cultivated plants, that is) as exposed bedrock or bog. In that case, the more practical approach is to select a site with reasonably good soil, the kind of soil in which you might plant a lilac bush or a vegetable garden.
The influences of climate—the weather conditions prevailing over a general area over a long period of time—are manifold. Climate dictates what fruit plants will thrive, even survive. Climate is one factor in the potential for disease. And finally there’s the fruit itself; climate can hold sway over a fruit’s appearance, even its flavor.
Fruit plants vary in their tolerance for cold. Low temperatures may kill only fruit buds (in which case you lose the forthcoming season’s crop), may kill occasional branches, or may kill the whole plant. For a general idea of the average minimum winter temperatures where you live, consult the USDA Plant Hardiness Zone Map. Wavy lines overrunning this map bracket each zone, from 1 through 11, delineating the average annual minimum temperature within each zone. As you look through nursery catalogs and read tags on plants in local nurseries, note the USDA Hardiness Zones listed for the fruits. Peaches, for example, are generally adapted from Zones 5 to 9, corresponding to regions experiencing average winter lows of about –15°F to about 25°F. Specific varieties may have narrower adaptation; ‘Desert Gold’ peach, for example, is adapted to only warmer regions, Zones 8 and 9. Knowing the cold-hardiness zone where you live and the hardiness limits for plants helps you decide which plants will thrive and bear well in your yard.
The USDA map covers the whole country, so it cannot help but generalize average low temperatures over relatively large areas. If you are new to an area or haven’t before kept tabs on the weather, rely on what neighbors have to say about winter minimums as well as advice from your local Cooperative Extension office (find yours on the Cooperative Extension System Offices page). Even better, back up your own and others’ experience with some hard facts by using a minimum/maximum thermometer.
A minimum/maximum thermometer, besides telling the current temperature, registers the minimum and maximum temperatures that were reached since the thermometer was last reset. If the mercury plummets some blustery winter morning to –20°F at 3 a.m., then “warms” to –5°F when you awaken at 6 a.m., you will know the actual low temperature. (Your plants already knew!)
Keep in mind that the actual low temperature during any winter will not necessarily be the same as the “average minimum” temperature as spelled out on the USDA map. If you live in Vermont or North Dakota, do not let a string of atypically warm winters lull you into planting nectarines. Use the USDA map along with your own observations and those of your neighbors. Then again, winters have been warming, so, depending on your gambling spirit, you may want to try to push some limits. Try growing citrus in Georgia, perhaps?
Fruit Garden Chilling Hours
Winter temperatures are as important to gardeners in warm regions as they are to gardeners in cold regions, not for absolute cold temperatures but for duration of cool weather. Deciduous fruit plants (plants that lose their leaves and go dormant in winter) will not resume growth in spring until they experience an accumulation of a certain number of hours of cool—not cold—weather, commonly known as “chilling hours.” Such chilling occurs, for most plants, between 30°F and 40°F. Temperatures much higher or lower than this amount do not put hours into the cumulative chilling “bank.”
The amount of chilling required varies with both the type and variety of fruit. Most apples, for example, need a total of 1,000 to 1,500 hours of chilly temperatures before they will again begin growth in spring. So consider that chilling bank if you want to grow deciduous or temperate-zone fruits and live in an area with short, mild winters, such as in northern Florida, southern California, or a rough belt connecting those regions. If winters where you live are short and mild, plant fruits such as figs, pomegranates, and grapes, which need little or no chilling. If you must have apples or other fruits of colder regions, plant “low-chill” varieties such as ‘Beverly Hills’ apple and ‘Desert Gold’ peach that require fewer than 300 chilling hours.
This chilling business also works the opposite way, farther north. Where winters are moderately cold, chilling requirements of low-chill plants are fulfilled early in winter. The result: Overeager blossoms, held back by cold and now waiting only for warmth, are liable to open too early and be nipped by subsequent frosts. Therefore, do not plant low-chill fruits in northern regions.
Not all low-chill fruits come from warm winter regions. Plants native to places where winters are long and steadily cold are also genetically programmed to begin growth after only a short amount of chilling. In their native habitats, the chilling requirements for such plants are not fulfilled until late spring, because cold temperatures are generally below the 30°F to 40°F range for the duration of the long winter. In these regions, spring growth must be quick for the fruits to ripen within the relatively short growing season.
Where winter temperatures fluctuate, with many days in the 30°F to 40°F range, as occurs over much of the continental United States and Canada, chilling hours slowly accumulate through the winter. As a result, if plants such as apricot, which come from regions with long and steadily cold winters, are planted in these regions, they bloom early and their blossoms are often nipped by late frosts.
How cold your winters get—the actual depth of cold—may be the most important consideration about your climate for fruit growing, but it’s not the only consideration. If you live in a high-mountain or far-north location where growing seasons are short or if you live in a coastal region where summer temperatures remain relatively cool, you may also have to take your summer weather into account. Heat-loving fruits such as pawpaw, pomegranate, and late-season varieties of grapes may not ripen in such climates.
On the other side of the coin, too much heat can be detrimental to any plant. Heat damage doesn’t result in the dramatic wilted flowers or leaves that follow immediately on the heels of a freezing night. Heat damage is more gradual and cumulative. Plant growth may be stunted, leaves may turn pale or brown, and root function may suffer.
The American Horticultural Society’s Plant Heat Zone map, like the USDA’s Hardiness Zone map, is overrun with wavy lines that divide the country into zones. On this map, the zones indicate the average number of days per year that the temperature is above 86°F, the temperature at which heat damage might occur. The zones range from Zone 1, with an average of less than one day above 86°F each year, to Zone 12, with an average of more than 210 days above 86°F each year. This map was developed relatively recently and, as such, should be considered a work in progress, useful to tell you where and which fruit plants might suffer “heat stroke” or be unable to ripen thoroughly.
Plants’ recommended heat zones are generally listed following their recommended cold-hardiness zones. So sweet cherry, for example, is 5–9, 8–1, with 5–9 being its range of cold-hardiness zones and 8–1 being its range of heat zones.
Rainfall is less limiting to what you can grow than is temperature. Most plants need a steady supply of water throughout the growing season, but you can water your plants if rainfall amounts are inadequate. Pomegranates and sweet cherries tend to split if it rains as these fruits are ripening, but you can get around these problems with timely harvest and choice of nonsplitting varieties.
“Everyone talks about the weather, but no one does anything about it.” Mark Twain, who penned that line, must not have grown fruits. Winter cold zones, summer heat zones, and Mark Twain’s statement notwithstanding, you can do something about the weather, by seeking out or creating microclimates.
If you’ve ever leaned back against a sunny brick wall to enjoy its warmth on a winter day, you’ve experienced the effect of a microclimate, which is a small area where the climate is different from that of the general climate. In this case, the wall caught and held the heat and kept you warmer than you would have been standing in the cold air a few yards away. Microclimates aren’t dramatically different from the general climate but may be different enough to benefit your fruit.
Preventing Frost Damage in a Fruit Garden
Microclimate comes into play with spring frost hazard. Most fruit plants bloom in late winter or spring, making their blossoms vulnerable to subsequent, hazardous spring frosts. Such frosts rarely kill the plant, but can kill blossoms and the chance of fruit for that year. A difference of a few degrees of temperature can spell the difference between a bountiful harvest and just a few, or no, fruits. Hence the importance of a microclimate (see an illustration of working with microclimates).
The way to get your fruit plants to sidestep late frosts is to keep them from rushing into bloom; that is, keep your plants “asleep” longer. Do this by planting them in a spot where everything warms up slowly. Because water moderates temperature changes, areas least likely to experience damaging late frosts are those near oceans or large lakes or rivers. You don’t want to relocate? Then delay bloom by looking around your yard for a microclimate that is the opposite of the microclimate near that sunny wall—one that keeps a plant cool. Bloom will be delayed on a north-facing slope as well as near the north side of your home, garage, or any other wall. Near that wall, the plant is shaded from low winter sun. Just make sure you plant far enough away from the wall so that summer sun, higher in the sky than winter sun, will fall on it.
Late winter and early spring freezes commonly occur on still nights when the sky is clear. Under such conditions, cold air, being heavier than warm air, hugs the ground and flows downhill, filling up low spots as would water. Also avoid spring frost damage by not planting in low-lying areas, especially if you are growing a low-growing, early-blooming plant such as strawberry. My property is basically flat, but on clear cool nights I can feel the temperature difference in spots even just a few feet lower than the surrounding ground.
Don’t forsake the pleasure of growing fruit for lack of a site free from spring frosts. Grapes, blackberries, persimmons, raspberries, jujubes, figs, and a number of other fruit plants bloom long after all chance of frost is past. (And grapes blossom on secondary buds if their primary buds get zapped by frost.) Other fruits, such as gooseberries, cornelian cherries, and currants, have blossoms that are resistant to frosts. And you can easily drape a blanket over a strawberry bed if frost is predicted on a night when the plants are in bloom.
Minimizing Winter Cold Damage
Microclimate influences winter cold also. Because cold winter winds sweep across the tops of hills, the ideal location for fruit plants is right on a slope, rather than at the top or, because of spring frost hazard, the bottom. Make sure that no obstructions, such as walls or dense hedges, stop the flow of cold air down a slope. The microclimate created by the sunny brick wall mentioned earlier, or any masonry wall basking in sunlight, also mitigates winter cold by absorbing the sun’s rays and then reradiating heat at night to warm any nearby plants. Plants experience the same effect from proximity to a paved terrace, path, or driveway. Near walls (except on slopes where those walls will pool cold air) or paving is thus a good choice for planting fruits that are borderline winter hardy. Be careful with early bloomers though, because that same warmth will coax earlier growth from these plants.
Fluctuating temperatures can wreak as much havoc on plants as can extremes of temperature. Tree bark is especially susceptible to such fluctuations, which can cause cracking and then infections. Sun beating down on bark on a cold, sunny winter day heats it up, but as soon as the sun drops beneath the horizon later in the day, the temperature of the bark plummets. One way to avoid these temperature swings is to paint the bark white to reflect the sun’s heat during the day. Use white latex paint diluted with an equal part of water. An added benefit of this whitewash is that it deters certain boring (as in “makes a hole”) insects.
Preventing Heat Damage in a Fruit Garden
On the other hand, if your plants need cooler summer temperatures than your region generally offers, use cooler microclimates such as partly shaded sites (less than full sunlight will sacrifice some yield, but you may be willing to give that up to grow the fruit). You can also try north-facing slopes or near the north sides of walls or buildings.
Pollination is the transfer of pollen from the male parts of a flower (the anthers) to the female parts of a flower (the stigmas) (see an illustration of the anatomy of a flower). Within the flower, pollen from the anthers unites with egg cells in the stigmas to form seeds, and in so doing stimulates the development of the fleshy covering around the seed—the fruit! (Also, check out how bees pollinate flowers!)
Pollination can stimulate fruit formation only if the pollen comes from a flower of the same type of fruit. Thus an apple flower can be pollinated by an apple flower but not by a strawberry or pear flower. (There are possible exceptions.)
A flower can be male, female, or both. If a plant has flowers that are either male or female, but both kinds are on each plant, that plant (filbert is an example of this type of plant) is monoecious (Greek for “one house”). A dioecious (Greek for “two houses”) plant has only one kind of flower, either male or female, on each plant. Persimmon trees are generally either male or female. Most cultivated fruits have what botanists call perfect flowers; that is, they are monoecious and every flower has both male and female parts so they can provide pollen and form fruit.
Self-Unfruitful and Self-Fruitful Plants
Not all plants with perfect flowers can set fruit with their own pollen. If they cannot, they are self-unfruitful. Flowers that are self-unfruitful need cross-pollination and will not set fruit unless they receive pollen from a different variety of the same type of plant. Apples need cross-pollination, so a ‘McIntosh’ tree needs another variety, such as ‘Red Delicious’, nearby to bear fruit. The ‘Red Delicious’ will similarly bear a crop using pollen from the ‘McIntosh’ flowers.
Certain varieties of fruits may have special pollination needs. ‘Magness’ pear produces poor or little pollen so is incapable of pollinating any other pear. Pears generally need cross-pollination, but not every marriage between two varieties is fruitful. Although ‘Bartlett’ and ‘Seckel’ each produce good pollen, an innate incompatibility prevents them from cross-pollinating each other. Hence three different varieties of pears are needed if you want fruit from the ‘Magness’ pollinator or if you want to grow ‘Bartlett’ and ‘Seckel’. You will find this sort of information listed with the description of a variety in nursery catalogs.
The most obvious way to provide a pollenizer, when needed, is to just plant the variety you need. To pollinate effectively, plants should be within 100 feet of each other. Before you choose pollenizers, also make sure that their bloom times overlap with the variety you’re trying to pollinate. ‘Gravenstein’ apple, for example, blossoms very early, so it would be a poor choice to plant with a late-blooming variety of apple, such as ‘Rome Beauty’. Generally, there is good overlap of bloom times for different varieties of each kind of fruit.
There are workarounds for planting a pollenizer. Perhaps your neighbor is growing a plant that can sire your plant(s). If not, perhaps you can convince your neighbor to grow such a plant, in which case, if the fruit is perfect-flowered, you’ll both reap rewards. Perhaps pollen could be supplied by suitable wild plants nearby. If you know of a suitable pollenizer plant that is not nearby, cut off some flowering branches while the plant is in bloom, then plop their bases into a bucket of water set near your blooming plant. The bouquet’s pollen will remain viable long enough to pollinate your plant.
Another alternative to planting a cross-pollenizer is to graft a single branch of a pollenizer plant onto your plant. If the pollenizer also produces good fruit, then you will be able to harvest two different varieties from your single plant.
Not all fruits require cross-pollination to produce a crop. Fruits such as strawberries, raspberries, and most peaches have perfect flowers that are self-fruitful, meaning they can produce fruit with their own pollen, so you can plant just one variety and harvest a full crop.
Self-fruitful and self-unfruitful are two ends of a spectrum, and some plants lie between these two extremes in their pollination needs. In such cases, it pays to provide for cross-pollination, because doing so coaxes partially self-fruitful plants to yield more and bigger fruits.
A few plants set fruit without any pollination whatsoever. Among these plants are certain varieties of persimmon, fig, and mulberry. In such cases, not only can you forego providing a pollenizer branch or plant but the fruits themselves are seedless.
Choosing a Plant for Its Size
Every fruit plant needs adequate elbow room. A strawberry plant needs its 1 square foot of space and a full-size (standard) apple tree needs its 500 square feet of space, in each case so the leaves of the plant can bathe in sunlight and drying breezes. Such conditions promote good yields and limit disease problems.
The distance you should set your plant away from other plants, buildings, or walls depends on how big your plant(s) will eventually grow. Eventual size is determined by the richness of the soil, pruning, and a plant’s inherent vigor. By pruning, you could keep a plant to almost any size. For example, cordon apple trees—just single stems of fruits—can be planted as close as 2 feet to 3 feet apart with appropriate rootstocks and pruning techniques.
Except in cases of extreme soil conditions or careful and constant pruning on your part, the inherent vigor of your plant will be the main determinant of its ultimate size. For some types of fruit plants, such as apples and pears, you can choose the eventual size of the plant you want from a range of sizes. With tree fruits, a full-size plant is called a “standard.” “Dwarf” trees are smaller in varying degrees. Any good nursery that sells dwarf trees should specify just how much different in size the trees are from standards.
Dwarf Versus Standard Plants in a Fruit Garden
A plant might be a dwarf either because it’s naturally small or because it’s been grafted onto a special dwarfing rootstock. The “rootstock” of a grafted plant provides merely the roots and a short length of trunk upon which is grafted the stem of a desired variety; all growth above the graft, which always remains at the same height, is of the grafted variety. A ‘Northblue’ blueberry bush is an example of a plant not propagated by grafting; it is naturally small and will never grow to the size of a naturally large ‘Bluecrop’ blueberry bush. Apple trees are examples of plants propagated by grafting, and a ‘McIntosh’ apple tree might grow to 25 feet grafted on one rootstock (MM.111), to 15 feet grafted on another rootstock (MM.106), or to only 6 feet grafted on yet another rootstock (M.27).
Fruit size is not affected by plant size. All of the ‘McIntosh’ fruits will be the same, but the ‘Northblue’ fruits are different from the ‘Bluecrop’ fruits. Because of their smaller size, dwarf trees are generally easier to manage than full-size trees. You have less need to climb ladders or climb among the branches because most or all pruning, thinning, and harvesting can be done with both of your feet planted firmly on the ground. Smaller plants are also easier to spray, should this be necessary.
Another advantage of dwarfs is that you can cram more of them into a given area. Instead of seven bushels of fruit from one large ‘McIntosh’ tree, you could harvest a bushel and a half from each of six dwarf trees occupying the same space as the single large tree (and each tree could be of a different variety). Not only do you get more variety in apples but, because small trees “harvest” sunlight more efficiently than large trees, you’ll also get a greater total yield. Large trees shade themselves, resulting in a lot of the plant’s energy going to supporting wood that carries neither leaves nor fruit. Or you could plant a couple of dwarf apple trees, a couple of dwarf peach trees, and a couple of dwarf plum trees in that same space. With smaller trees, you can harvest a greater variety of fruits and spread out the harvest over a longer season. Yet another advantage is that, in many cases, grafted dwarf trees bear their first crops sooner than grafted full-size trees.
With that said, a larger tree might better suit your needs. Perhaps you enjoy putting up a mess of applesauce or canned peaches all at once. Generally, large trees tolerate drought, poor fertility, and other undesirable soil conditions better than dwarf trees do. With age, a large tree also develops a majestic quality and provides shade and limbs upon which to climb. And besides, for some types of fruits, such as persimmon and avocado, you have no choice in tree size.
Choosing a Plant for Its Productivity
Part of the skill in raising fruit is to produce enough of it, in steady supply, over a long season. You will want your plants to yield enough to satisfy your needs but not so much that the excess is left rotting on the plant or on the ground. (Neighbors and friends can help you out of the latter dilemma.) A selection of plants that bear fruit over a long season lets you spread out the harvest and preserve the bounty at a more leisurely pace and extends the season during which you can enjoy fresh fruit (see a chart of approximate fruit yields of common fruits). That is how I am able to eat fresh blueberries from the middle of June well into September—the season opens with pickings from my ‘Duke’ bushes and closes with a harvest from my ‘Elliot’ variety.
This excerpt has been reprinted with permission from Grow Fruit Naturally: A Hands-On Guide to Luscious, Home-Grown Fruit by Lee Reich, published by The Taunton Press, 2012.