Climate and Seasons: Effects on Plant Growth

2. OBJECTIVESThe student will be able to… • Relate the major characteristicsof the seasonsin terms of plantgrowth.

3. OBJECTIVESThe student will be able to… • Explain the effects of frost, snow, sleet, hail, and frozen soil on plant growth. • Identify microclimates in his/her immediate area. • Locate area on the USDA Plant Hardiness Zone Map and the AHS Heat-Zone Map. • Recognize outside areas with full sun, partialsun, and full shade.

4. CLIMATE AND SEASONS • All parts of the U.S. (except Hawaii & Puerto Rico) & Canada are considered in the “temperate zone”. • With normal seasons: spring, summer, fall, and winter. • Seasons can be classified as “wet” & “dry” in some areas. • Some U.S. areas are “tropical” or “subtropical”. • They do not experience frosts and freezes. • Mainland tropical zones in California & Florida may have variations of 20 - 30 deg. F in daytime highs and nighttime lows throughout the year. • The true tropics lie between the tropics of Cancer and Capricorn, 23 deg. north & south of the equator. • With negligible temperature variation through the year.

5. CLIMATE AND SEASONS True also of the desert Southwest.Winter rains are followed by a short, spectacular flowering spring, thena long, hot, completely dry summer. Figure 4-1 Desertification, enlargement of deserts due toclimate change, will affect ability of existing plants to survive. • California has a “Mediterranean climate”: • A wet winter season. • Short spring, starting in February. • Rain slowly tapers off. • Long summer/fall, until October. • Little or no rain falls for months.

6. CLIMATE AND SEASONS • The growth patterns of plants vary widely from season to season depending on the plant type. • Some are spring bloomers, others don’t flower until fall. • Some begin to grow as soon as snow has left the ground. • Such as asparagus. • Others produce no growth until all chance of frost is past. • Such as lilies.

7. CLIMATE AND SEASONSSpring • For the majority of plants in temperate zones, spring is when the majority of yearly growth takes place. • This yearly growth flush includes: • Leafing out of trees. • Emerging and blooming of bulbs. • Blooming and fruit setting in fruit trees. • New shoot growth in shrubs and trees. • Some plants, such as grapes, make all new growth for the year during this 1- or 2-month period. • Others, such as lawn grasses, continue to producenew growth as long as the weather is favorable.

8. CLIMATE AND SEASONSSummer • Summer is a period of maturing in plants. • Some plants have their flowering period. • Tomatoes and corn. • Others, which flowered in the spring enlarge/ripen fruits. • Such as fruit trees. • New, tender spring leaves toughen to a leathery texture. • Many plants accumulate energy in the summer to enable them to live through the long winter. • During which it will have no leaves and be completely dependent on the food stored in its roots and branches.

9. CLIMATE AND SEASONSFall • Fall is a transitional season for plants that live year- to-year & the end of life for those living one season. • Those surviving the winter engage mechanisms to will ensure their winter survival: • Dropping leaves & stopping new growth. • A nearly static state to await favorable growing conditions. • Plants that live one year must have produced seeds capable of sprouting in the next growing season. • And must have dispersed those seeds throughoutthe area by their own unique evolutionary means.

10. CLIMATE AND SEASONSWinter • For most plants, winter is a time of waiting. • When temperatures are below freezing, water is solidand cannot travel readily throughout the roots and stems. • Lack of water & leaves drastically slows biochemical processes in the plant, putting most in a state of suspended animation. • Until the return of favorable growing conditions. • Except evergreen plants such as pines, spruces, firs, junipers. • It is advisable to water evergreens during during periods of thaw when soil is able to take in moisture. • This can help avoid unsightly winter burn.

11. ELEMENTS OF CLIMATE • The elements combining to make up a climate include primarily: • Temperature; Precipitation; Humidity; Light; Wind. • Each has a wide range of variation and a dramatic effect on plant growth.

12. ELEMENTS OF CLIMATETemperature • Temperature, largely determines the geographic range over which a plant will grow. • Particularly minimum winter temperature. • The lowest temperature that a plant can withstandis called its cold hardiness or cold tolerance. • For many plants about 28 deg. F is the minimum because at this temperature the liquid contents of the plant cells freeze and the plant dies. • These plants are designated as frost-tender. • Includes many vegetables and flowers.

13. ELEMENTS OF CLIMATETemperature • Plants that are able to survive temperatures lower than freezing are called frost-hardy. • They vary widely in tolerance to subfreezing temperatures. • In some cases the woody portions or root system may be frost-hardy but not the flowers and leaves. • Some garden flowers die to the ground in fall but grow back from the roots the following spring. • Some houseplants and many tropical plants suffer chilling injury at temperatures less than 50 deg F. • This is why bananas turn black in the refrigerator.

14. ELEMENTS OF CLIMATETemperature • Minimum winter temperature limits areas where many plants can live. • For some plants lack of cold prevents survival. • Fruit trees such as apple & cherry; Flowers like peony & tulip. • For temperate-zone fruits, an adequate number of cold days per winter, the chilling requirement, is essential for normal growth and fruit production. • Such as apples and cherries. • Each type of & variety of fruit has its own specific requirement. • Each crop also needs a certain number of adequately warm days in order to mature. • The growing degree-day requirement.

15. ELEMENTS OF CLIMATETemperature • A baseline temperature below which very little growth occurs is established for each crop. • Subtracted from the average temperature for a given day. • These daily measurements can then be added and compared to an established standard for that cropto determine when the crop will mature.

16. ELEMENTS OF CLIMATEFrost • Understanding frost types & weather conditionsthat favor each is important because of damage done to frost-tender plants. • A frost can be one of two types: Radiation and hoar frosts.

17. ELEMENTS OF CLIMATEFrost • Radiation frost - occurs when the air is cool and calm and skies are clear. • Warmth from the sun accumulated by soil and plantsin the day is lost at night as heat radiating upward. • If the day was warm and the night only slightly below freezing, heat in soil & plants may last all night and offer frost protection. • If not, frost damage will result.

18. ELEMENTS OF CLIMATEFrost • When plants are covered by a barrier blocking flow of heat to the sky, frost can often be prevented. • Clouds form this barrier, and radiation frosts seldomoccur on cloudy nights. • On clear, protection by layers of newspaper, cloth, smoke, or plastic film can serve the same function. • Sprinkler irrigation of plants is also used to prevent frost.

19. ELEMENTS OF CLIMATEFrost • The second type of frost is caused by a cold air mass moving into an area. • Carrying off heat from the plants, which are then frosted. • Frost often leaves ice crystals on plants and the ground in the early morning, are called hoar frosts. • Called black frosts, because the first sign of their occurrence is the blackening of injured plants. • Appearance of frost in some areas, but not in others close by is due usually to elevation differences. • Cold air is heavier than warm air & flows down tothe lowest area.

20. ELEMENTS OF CLIMATEFrost • The northern parts of the U.S & almost all of Canada experience freezing of the ground during the winter. • In unseasonably cold years many plants may “freeze out” as a result of the temperature around the root zone being too cold for the plant to survive. • Freezing of the soil causes water contained in it to expand, and may cause frost heaving. • Soil pushes up around the roots of plants leaving cracks over the root area, exposing them to drying winter winds. • Gardeners frequently lay a thick layer mulch over rootareas of plants they know to be borderline cold-hardy.

21. ELEMENTS OF CLIMATEPrecipitation • Precipitation can take many forms including rain, snow, hail, and sleet. • Rain is of greatest value to outdoor plants. • Lack of rainfall is a limiting factor to plant growth. • Particularly in the western U.S., where irrigation is essential to grow plants.

22. ELEMENTS OF CLIMATEPrecipitation • Excessive rain or rain occurring out of season can be as detrimental to plants as lack of rainfall. • Excessive rain can kill plants adapted to dry areas. • Unseasonable rain near harvest can make strawberrieswatery-tasting, and split unpicked apples & grapes. • Frequent rains spread plant diseases by splashing microorganisms from one leaf to the next. • Triggering the growth of dormant disease organisms present on plants.

23. ELEMENTS OF CLIMATEPrecipitation • Snow cover plays an important role in plant survival in areas with cold winters. • Protects low-growing plants low-temperature damagedue to the chill factor or drying injury due to sublimationof the frozen water from the plants. • In sublimation, frozen water turns directly into its gaseous state without ever melting. • The process used in the food preservation technique known as “freeze drying”. • Requires energy in the form of heat, taken from the plant. • Damage is caused by the water lost from internalparts of the plant, as well as from the surface.

24. ELEMENTS OF CLIMATEPrecipitation Figure 4-2 A rosebush shows effects of a heavy snowload & freezing rain. Courtesy Susan Brandt Graham. • Sleet, hail, and freezing rain can be very injurious to plant health. • Sleet & hail tear leaves & bruise or knock off fruits. • Freezing rain often causes branch breakage on trees. • Heavy snowfall can cause breakage due to its weight.

25. ELEMENTS OF CLIMATEPrecipitation • Dew is most likely to occur when the air is warm and humid. • After sunset, air temperature drops, and the atmosphere is unable to contain the water it held during the daytime. • Water precipitates out, in the small droplets called dew. • Although its effect on most plants is not great, it can be a factor in the spread of diseases in turfgrass. • It is also an important water source for plants that absorb water readily through their leaves.

26. ELEMENTS OF CLIMATEHumidity • Humidity may determine how well a plant will grow. • Defined as the amount of water the air contains relativeto the amount it is capable of holding. • At that specific temperature. • Often higher humidity improves plant growth by reducing the rate at which plants lose water. • Low humidity will not seriously hinder growth of most outdoor plants if there is adequate water around the roots. • Indoors plant in cold-winter climates are commonly damagedby insufficient humidity.

27. ELEMENTS OF CLIMATEHumidity • In coastal California climates, the moisture from fog andmist is absorbed by plants, supplementing meager rain. • At the same time this vapor retards loss of water from leaves. Figure 4-3 Fog in a redwood forest of coastal California.The moisture-laden air is the only source of water duringthe dry summer months. Photo by Rick Smith. • Fog and mist, can influence plant growth greatly.

28. ELEMENTS OF CLIMATELight • Light duration, intensity, and quality affect growthof outdoor and indoor plants. • May control flowering and growth rate. • Light duration in any particular region depends on distance from the equator and season. • At the equator, day & night are equal length all year. • North or south of the equator, days become longer in the summer and shorter in winter. • The further from the equator, the greater the difference between the longest summer day and shortestwinter day.

29. ELEMENTS OF CLIMATELight • The duration of daily light a plant receives is important, as it determines the period of time it can manufacture the carbohydrate necessary for growth. • Duration of the night also affects the start of some plant processes, such as flowering. • Light intensity or brightness affects photosynthesis because, in general, the brighter the light intensity, the more photosynthesis occurs. • Moderate to bright intensities are most beneficial. • Latitude will alter intensity.

30. ELEMENTS OF CLIMATELight • At the equator the sun passes overhead all year. • In the northern U.S. it is nearly overhead in summer. • Low in the southern sky in winter. • Winter intensity is lower because of the distance through the atmosphere the rays must travel. • Lesser amounts of light signals plants to become dormant. • For evergreens, lower light intensity of winter is sufficient to continue photosynthesis and sometimes growth. • Indoor plants can be seriously retarded by the decrease in light, as many are already growingat subsistence light levels.

31. ELEMENTS OF CLIMATELight • When buying plants for the garden, it is essential to know light preferences of plants being purchased. • One must know the approximate amount of light the area receives in order to choose a plant that will grow healthily.

32. ELEMENTS OF CLIMATELight • Full sun - found on the south sides of houses. • Or where there are no trees, shrubs, or structures to block light. • Full sun can also be on the west side of houses in the western U.S., as the afternoon sun in these areas can be very strong. • Areas around the home can be classified as: • Full shade - areas in which the sun rarely shines directly. • Northern sides of houses, narrow areas between houses. • Under large trees & other areas shaded almost all day. • Partial-shade - areas which receive direct sunlight for about one-third to one-half of the day. • East- and west-facing walls of houses • Under small/finely foliaged trees that admit “filtered sun”.

33. ELEMENTS OF CLIMATEWind • Wind is the fifth climatic element governing growth. • Ocean wind limits the number of plants that can be grown near the shoreline. • By salt spray, which browns plant leaves. • By the intensity, which whips and breaks leaves and branches. • Hot desert winds increase the rate of moisture loss from soil & plant leaves, intensifying drought conditions. • Subzero winds in cold northern areas damage evergreens by removing moisture from foliage, freeze-drying it.

34. FACTORS MODIFYING CLIMATE • Natural factors modifying climate include distance from the equator, elevation, terrain, and the nearby presence of large bodies of water.

35. FACTORS MODIFYING CLIMATEElevation • Changes in elevation can give areas only a small distance apart completely different climates for plant growth. • The higher the elevation of an area, the colder the average year-round temperature • Every rise of 300 feet (91. 4 meters) causes an average temperature decrease of 1 deg. F.

36. FACTORS MODIFYING CLIMATE Terrain (Topography) • Changes in terrain alter climate, particularly rainfall. • Most rainstorms move from west to east in North America. • In a narrow range of hills, west-facing slopes often receive much more rainfall than east-facing slopes. • Heaviness of the water in rain clouds prevents them from passing over mountains until most of the precipitation hasbeen released. • The drier region on the eastern slopes often is referredto as a rain shadow.

37. FACTORS MODIFYING CLIMATE Terrain (Topography) Cool air, heavier thanwarm air, will flow downa slope and collect at the bottom, a phenomenoncalled air drainage. Plants growing higher onthe slope are less likely tobe damaged by cold thanthose at the bottom. Figure 4-4 Typical cold-air drainage on sloping land. • Sloping terrains can vary in temperature by several degrees from the top of the slope to the valley.

38. FACTORS MODIFYING CLIMATEBodies of Water • Large bodies of water like the Great Lakes & oceans exert strong effects on the climate of nearby land. • The enormous volume of water absorbs heat in summer, making adjacent land cooler, and gives it off in the winter, raising the temperature. • On the North American continent, the influence of large bodies of water on agriculture is considerable. • Warmer winter temperatures along the Great Lakes make these regions large commercial growing areas for fruits such as grapes, cherries, and peaches. • Most of the Pacific coast is warm enough to grow certain vegetables all winter, but inland these crops would freeze.

39. FACTORS MODIFYING CLIMATEClimate Modification by Humans • People can modify climate either intentionally or unintentionally. • Among the most widespread unintentional causes of climate change are air pollution and consequent smog. • Smog affects plant growth by temperature modification,acting like an insulation layer, preventing heat from escaping. • Particulates settle onto leaves & decrease light reaching plants. • Smog affects plant growth is through foliage injury by toxic gases entering leaves, causing them to partially brown and sometimes to die. • Plants classified as intolerant (many pines, for example)cannot be grown in smoggy areas.

40. MICROCLIMATES • Microclimates are small areas with slightly different climate characteristics than the surrounding land. • May be less windy, shadier, moister, warmer, or in any other way different from the typical climate. • These differences affect plants, sometimes helping and sometimes hindering growth. • Microclimates may be either artificial or natural. • They can be formed by the natural terrain & vegetation. • Or unintentionally created by structures, fences, roadways.

41. MICROCLIMATES In some cases they makeit possible to grow plantsnot normally consideredcold-hardy in that area. Figure 4-5 A microclimate for a fern wouldbe under trees or against a north wall. Courtesy of B. J. Fundaro, Sonoma StateUniversity, Rohnent Park, Calif. • Although they often go unnoticed, they can be used by the observant gardener to provide the specialized growing conditions favored by different plants

42. MICROCLIMATESOutdoor Microclimates • A natural microclimate example is a frost pocket. • Colder, possibly moister due to water runoff. • Suitable for moisture-loving plants not easily damaged by cold. • Another natural microclimate is found under trees. • Shadier/cooler in summer, good for shade-loving plants. • Or growing indoor foliage plants outdoors in summer.

43. MICROCLIMATESOutdoor Microclimates • Plants in the microclimate under the eaves of a house live under different environmental conditions than plants living away from the house. • Shielded from rainfall by an eave, so the soil will be drier. • The wall may afford protection from cold or drying winds • Radiates warmth from the heated dwelling.

44. MICROCLIMATESOutdoor Microclimates Frequently the case with parking lot trees, which become overheated dueto heat radiating from the asphalt. Figure 4-6 Scorch on maple due toexcess heat. Courtesy Dr. R. E. Partyka, Columbus, Oh. • During cool periods, additional warmth speeds upor prolongs growth, but if a wall faces south it may be excessively hot in summer & damage can occur.

45. MICROCLIMATESOutdoor Microclimates • At night when temperatures drop, objects begin losing heat to the cooler night air. • Heat radiating from the ground and buildings canprotect plants from frost & extend the growing season.

46. MICROCLIMATESOutdoor Microclimates • Wind can be intensified or lessened in a microclimate. • A plant by a wall will generally receive wind protection unless it is directly in the path of prevailing winds. • When two walls are parallel, a wind tunnel can be formed, and wind conditions will be worse therethan in a completely unprotected area. • Frequently formed between closely spaced buildings.

47. MICROCLIMATESIndoor Microclimates • Indoor microclimates with varying temperature,light, and humidity are found in houses/apartments. • Upstairs rooms may be warmer than downstairs ones. • A basement may be up to 20 deg F cooler • The north side of the house may be cooler than the south. • Even within a single room, cool microclimates willbe found adjacent to windows in cold-winter areas. • Because of cold entering through the glass. • Microclimates of varying humidity are also common. • In the kitchen and bath, evaporation raises the humidity. • A basement is also usually humid.

48. MICROCLIMATESIndoor Microclimates • Light microclimates are easy to detect, being governed by the size and location of windows. • The farther from a window a plant is, the less light it will receive, and each foot/meter of distance can be thoughtof as a different microclimate.

49. ADAPTIVE STRATEGIES OF PLANTSFOR CLIMATE TOLERANCE • Plants have evolved adaptive strategies to copewith adverse environmental conditions. • The most common adaptation is winter dormancy. • Plants in desert areas develop the ability to store water in their leaves, making leaves fleshy & thick. • Cacti take this to an extreme in that they have no leaves. • Only a thickened stem that forms the bulbous body of the plant.

50. ADAPTIVE STRATEGIES OF PLANTSFOR CLIMATE TOLERANCE • A most interesting example is the “baby toes” plant. • Native to the Cape Province of South Africa. This small cone-shaped plant lives almost entirely underground with only a transparent “window” at the soil level through which light penetrates to the interior cells, for photosynthesis. Figure 4-7 Baby toes (Fenestraria sp.), aSouth African plant adapted to a very aridclimate. Paloma Colomer Arroyo, Jaen, Spain. • Desert plants (xerophytes) can protect themselves from excessive sun.