HOME FRUIT GROWING-- Outwitting the Weather

(Note:  this is the revised chapter from the original Fruits and Berries book that due to space considerations was unable to be included in the Fruit Gardener's Bible.)

            A friend visiting us from Mexico commented, “You spend lots of time talking about the weather. We hardly ever mention it at home.” Our daughter asks why adults are always talking about the weather. We realized they were right. The weather plays an important part in our lives because it constantly affects our plans, as it does those of most gardeners. About forty years ago, I began to keep a daily record of weather and temperature, hoping that the information would help us better plan our growing program. Two decades later, all I really knew for sure was that New England weather is cussedly unpredictable, which any Yankee could have told me in the first place.  Now I can blame the extremes in our weather either on El Niño if it is happening that year, or on global warming. We have a saying in Vermont, which I imagine many other states have as well, that if you don't like the weather, wait a minute until it changes.

            Our weather may change several times a day, or get bogged down and stay the same every day for six weeks. The last frost of spring hits our crops in northeastern Vermont any time from late April to late June, and the first fall frost may come as easily as late august or as late as early November. We often joke about what day summer occurred this year.  Snow might arrive first in mid-September or in mid-December, and snowstorms of a foot or more have descended upon us in late May.

            Nearly every part of North America has similar surprises on the weather scene. Each year we hear of crop failures in one area or another due to unusual weather conditions from droughts to floods. Whether in New Jersey, Idaho, Minnesota, or even the Deep South, sudden temperature changes occasionally ruin the fruit crop. Few areas can be absolutely certain of a good harvest every year.Burrrrrrrr, It's Cold!        

            Of the weather variables that can affect fruit crops, other than water, a main one is temperature.  In warm climates this can relate to the need for chilling, already described, but in many areas the concern is winter cold.  There are many ways in which cold weather can affect trees, and even the experts are baffled by some forms of winter injury. Extremely low temperatures can cause damage, but, surprisingly, it isn’t always the frigid temperatures that do the most harm. Injury is sometimes most severe during mild winters, because sudden fluctuations can cause as much damage to trees as low temperatures. A long January thaw may induce the tree to start growing, or a warm sun in March may quickly heat its brown bark. In both cases the return to below-freezing is a severe shock and can even be fatal to the tree.

            It also depends on when the cold weather occurs.  Hardy plants, both herbaceous perennials and woody trees and shrubs, develop their resistance to cold gradually during the fall.  While they may not take even mild sub-freezing temperatures in October, they can tolerate much colder in January when fully hardened.  A similar but reverse process happens in spring, which is why early-blooming trees are often damaged by spring frosts.

            Any long duration of cold can hurt a tree, too, as can extended periods of wind chill. Like animals and humans, a hardy tree can stand considerable cold for a short period, but it will suffer if the situation continues for days. So even if a temperature isn't extremely cold, if it lasts long enough it can cause similar damage.

            You may not discover winter damage until spring, when whole limbs may fail to leaf out. Or you may notice large cracks where the bark of the trunk has split open, loosened, and started to come off. These open wounds create ideal conditions for fire blight, cankers, rots, and other infections. Inspect your trees in later winter and promptly deal with any injury.   Choose a warm day when the wood isn’t frozen, and cut off all limbs damaged by ice or snow.

            Weather also often causes stress and subsequent damage to trees and plants that may not show up until later in the growing season. One spring, following a dry summer and hard winter, many of our young trees leafed out beautifully, only to wither and die within a few weeks. The long period of stress had weakened them enough so they didn’t have the stamina to continue to grow.


What Trees Are Hardy in Your Area?

            When buying new trees, select kinds that are acclimated and can stand the weather expected for your region. If you have extra room, it is always fun to experiment with a few that are intended for a warmer zone (see next section on Microclimates), but for most of your planting you’ll want to stack the odds in your favor.  There is a great difference in hardiness sometimes among cultivars, so pay attention to the hardiness for each.  Just because a particular fruit type is listed for a certain hardiness range, doesn't mean all cultivars will live in all the zones.

            To be successful in your orchard, a fruit tree must meet several requirements. It must be able to make its growth during the first half of the growing season, then stop growing and harden up all new growth before the first frost. Some people assume that a tree’s hardiness is determined only by the cold temperature it can stand. Actually, a short growing season may limit your choice of fruits more than the lowest temperatures. Certain peaches, plums, and nuts are often advertised as being hardy to –20°F. What is left unsaid is that the trees need a long growing season to properly harden the wood so that it can stand those low temperatures. Some tree fruits, as well as many grapes, nuts, blackberries, and blueberries that were developed in warm zones are still growing when the first fall frosts hit in certain areas of zones 3, 4, and 5. Since their new wood is still green and soft, the moisture-filled cells freeze and rupture. Native plants to a region have become adjusted to local conditions, and the shortening days trigger their growth mechanisms to stop growing and harden their wood before frost. Imported trees (from a milder region) are often not able to do this, and not only continue to grow late in the fall, but also may start to grow during the first warm week in early spring. "Provenance" refers to this difference between adaptation to climate among members of the same species that originated from different climate regions.

            Your tree also should be able to ripen its fruit before the first killing frosts of autumn and many late-ripening apples, such as Granny Smith, cannot do this and therefore are completely unsuited for northern gardens.

            Finally, during the winter the entire tree — fruit buds, branches, trunk, and roots — should be able to withstand the most likely coldest temperatures. It should also stay completely dormant all winter, and not begin to grow during a midwinter thaw.

Hardy Fruit Tree Traits

--All plant parts--buds, branches, trunk, roots--should withstand the coldest temperatures, and remain dormant during brief winter thaws.

--Fruit should ripen before the killing frost in fall.

--The growing season should match what the tree needs-- it should harden properly before fall frosts.


            Southern gardeners, and those in mild winter climates such as the Southwest and southern California, must be careful to choose the right plants for their climate too. Plants grown in temperate zones need a certain period of chilling during their dormant period, and can’t grow in the tropics. The length of winter chill needed varies from a long period for gooseberries to a far shorter one for pecans.  There may be quite a range of chilling needs among cultivars, especially for apples, with a separate list for low-chill cultivars.

            In addition to the other factors that determine hardiness, different parts of a tree may have different tolerances to cold. Often the roots and tops of some plants are perfectly hardy but their blossom buds are tender. Peach, plum, and pear trees all tend to bloom early, which makes them a special target of Jack Frost, but even later-blooming fruits like apples and grapes can be hit in areas that are prone to late spring frosts or in unusual years.  If you have a fruit tree that always leafs out and grows, but never seems to have fruit, this may be a cause.

            Although the requirements for a specific fruit tree might seem to limit your chances for growing it successfully, each planting zone has a number of cultivars of a fruit that will thrive there, and you have only to discover which do best in your area. See the chapters describing each fruit for help in making your choices.

            I sometimes hear older gardeners complain that the trees they buy these days don’t grow as well as they used to. In the good old days, the soil might have been better, or maybe  fewer insects and diseases were about, but a more likely reason is that trees grew better several decades ago because they came from a nearby nursery that grew them on the spot; or they were grafted by a local horticulturist who specialized in joining acclimated cultivars to native wild seedlings. By planting trees that had originated in the same neighborhood, the grower had just about everything going for him or her.

            Now, many of us have to plant trees that originated hundreds or thousands of miles away. Northern garden centers and mass markets often buy their stock from huge wholesale nurseries in the South or West, where a tree can be grown to selling size in only one of their long growing seasons. But there are a number of nurseries in each region with fruit trees as a specialty.  Often these have a much wider selection than you can find at a garden center, unless it is a large one specializing in plants, or a small specialty nursery with a fruit focus.

            People disagree over whether it really matters where a tree was grown. Is a McIntosh tree grafted on a Malling rootstock in Alabama really different from a McIntosh grafted on a Dolgo seedling in Quebec? I feel that the ones grown closest to home always do better, and whenever possible, these are the ones to buy. We once saw some Tennessee-grown sugar maples planted in Vermont as an experiment. The southern-grown trees held their leaves for a month after their Yankee companions had lost theirs. Likewise, a few years ago some Christmas tree growers in northern New England planted some balsam fir seedlings grown in other states. They were surprised the following spring when the imported trees started to grow much earlier than the native ones, and were considerably upset when a June frost killed all the new growth.

            Trees from one zone can acclimate to another zone if they are able to survive long enough. Both the maples and the firs imported from warmer areas are becoming more like their northern cousins each year. Trees that are vastly unsuited for another climate, however, have little chance of adaptation. Nectarines may never adjust to North Dakota, and the McIntosh will probably never grow well in Louisiana.

            We gardeners love to experiment and keep right on trying new kinds that are marginal in our zone, pushing the boundaries as you probably will too. It’s part of the joy of fruit growing.


Microclimates and Hardiness Zones

            Gardeners and gardening books and catalogs are always talking about "hardiness zones."  These are simply areas, as shown on a map, that share similar winter temperatures.  Although there are a few different maps you may see, the main one most refer to and that we'll use in this book is the USDA hardiness zone map.  A zone on this map shares the same annual, average, minimum winter temperature.  Colors, or zones, are in 10 degree (F) increments.  So zone 4 represents -20° to -30°F in winter.  If you look closely you'll see that these zones are further divided into half, a colder "a" and a warmer "b" region.  So a garden in zone 5b would on average reach -10° to -15°F. 

            This map is a good starting point, but there are several issues as already noted for winter survival to be consistent year to year.  Also note this is an average.  As I like to think about it, if one of my feet is in hot water and the other in cold, on average am I comfortable?  If it is -10° one night and -30°F the next, the average may fit the tree listing, but is the tree injured?  If you really want to hedge your bets and have a tree survive you should be looking at the extreme, not the average.  Looking over the climate data in for a local city near us over 10 years, the average temperatures indicate zone 5 (-20°F) at the coldest.  Yet over a couple years, the extremes got below this.  All it might take is one such year to kill a marginal fruit tree. For such trees, you may want to choose a more protected site on your property.         

            Although knowing your growing zone helps a great deal when choosing plants, every gardener soon finds out that within each zone there are many "microclimates" where a small area may be a zone or two warmer or colder than the surrounding area. Varying elevations, air drainage patterns, fog, frost pockets, prevailing air currents, proximity to bodies of water or buildings, and many other conditions cause these variances.  So while a fruit tree may be damaged by a low spot on your property where frost settles, it may be fine up higher. 

            It's not as easy to protect a large row of brambles or trees from frosts as it is to cover a row of vegetables with a frost blanket or your favorite flowers with a sheet.  Growers may turn on irrigation to protect spring buds, for as long as water is freezing on them they wont drop below freezing.  This usually isn't economical or practical for home orchards, going through so much water.  Another method is to keep the air circulating so frost doesn't form, as if there were a breeze.  Commercial growers do this with large fans, which again isn't practical or economical for most home plantings.

            It frustrates gardeners who bemoan the fact that while they can’t seem to grow a certain plant, the Joneses who live ten miles away can grow the same cultivar with no trouble whatsoever.  This is an example of "mesoclimate", between the microclimate as on a property or neighborhood, and the climate or hardiness zone over a whole section of the state.  Mesoclimate might be a valley, area near a lake, town versus country, or in my case the difference between living at a higher elevation than our town 3 miles away.  If you're looking to move or buy a first home and grow fruits, keep this in mind.


Artificial Climates

            In Iceland, Alaska, and parts of northern Europe, many fruits and vegetables are grown in glass or plastic greenhouses in order to survive the winter. This was popular in the 1800's in England with their famous large glasshouses and "orangeries" (for holding oranges over winter).  One of the oldest continuously harvested grapes is in a greenhouse at Hampton Court near London.  Since North America has a generous supply of land and an excellent transportation system, fruit growing in greenhouses is seldom done commercially. Some home gardeners use such houses as a hobby, however, and enjoy raising fruits and berries that wouldn’t ordinarily grow in their zone. We have friends who have cultivated dwarf peaches, pears, cherries, boysenberries, and grapes near the Canadian border in small greenhouses attached to their home.

            One of these greenhouses consists only of a wooden frame, which our friends cover with plastic in late summer and then uncover in late spring after all danger of frost. There is a small, above-ground swimming pool in the greenhouse to help maintain more even temperatures and provide humidity. The ground and pool soak up the daytime heat in early spring and fall, and release it during the cold nights, so artificial heat is seldom needed. During the winter the ground and even the pool freeze slightly, but since the inside temperatures are greatly modified, the widely fluctuating outside temperatures have little effect on the trees. With the longer growing season, the dwarf peach trees are able to complete their growing cycle and harden their new growth. As a result our friends pick a few dozen delicious peaches each year.

            Greenhouse fruit growing is demanding. In a tight building, the trees need extra water and, on sunny days in midwinter, the inside temperature may rise to over 100°F. It is necessary to provide ventilation by opening a window or installing an outside fan that works on a thermostat. The artificial climate also can provide good conditions for diseases and insects, since natural outdoor controls are missing, and this may require extra spraying. Also, unless there are plenty of bees in the neighborhood that you can let into the greenhouse at the time the trees are blossoming, you will probably need to pollinate by hand.

            All in all, however, fruit growing in a greenhouse can be an interesting hobby. Whether or not it is worth the considerable money and work involved is your decision. Most of us will probably choose to do our gardening outdoors, facing the weather head-on and paying attention to the cultivars we choose. Whether we live in Bismarck or Tallahassee, Bangor or Spokane, nothing is guaranteed, but with planning and care there should be enough successes to far outweigh the failures. That makes it all worthwhile.


            To sum up, I can’t overemphasize the fact that you shouldn’t make any large plantings of fruits for yourself or as a commercial venture until you have grown a few of them successfully in the same area for several years. This advice comes from past experience — my own failures and those of many other gardeners I’ve known.  I've learned it's better to try lots of fruits and growing systems and even several locations, and learn what works and what doesn't.  Make mistakes and learn on a small scale.  Yet I still talk to gardeners and new growers who want to start big.  Perhaps they're more of a gambler than I am.

            You can use various schemes to protect your trees from frosts, and your trees can tolerate and regrow from mild winter damage, but the best way to outwit the weather is to choose cultivars that are suited to your climate and minimize their stress with proper culture. If you live in the Deep South or a mild western climate, this means searching out plants that have the proper chilling requirements for your climate. If you are a northern gardener, you need ones that are hardy to the likely lowest temperatures and that are also able to complete and harden their growth during your growing season.