CMG GardenNotes #143 Plant Growth Factors: Temperature

Transcription

1 CMG GardenNtes #143 Plant Grwth Factrs: Temperature Outline: Temperature cnsideratins, page 1 Micrclimates, page 1 Influence f heat n crp grwth, page 3 Heat zne map, page 4 Influence f cld temperatures, page 5 Plant hardiness zne map, page 5 Plant hardiness, page 5 Examples f winter injury, page 6 Rest perid, page 8 Thught questins Explain the science behind the fllwing gardening questins. Why was there s much winter injury n my trees and shrubs? While it was dry and windy, temperatures were nt extremely cld. My arbrvitaes are bleached tan frm the winter. Will they green-up with spring temperatures? With the rather ht summer, will the apple and peach crp be as sweet as nrmal? Temperature Cnsideratins Temperature factrs that figure int plant grwth ptentials include the fllwing: Maximum daily temperature Minimum daily temperature Difference between day and night temperatures Average daytime temperature Average nighttime temperature Micrclimates Micrclimates are small areas where envirnmental cnditins may be different than the general surrunding area. The micrclimate f a garden plays a primary rle in actual garden temperatures. In muntain cmmunities, changes in elevatin, air drainage, expsure, and thermal heat mass (surrunding rcks) will make sme gardens significantly warmer r cler than the temperatures recrded 143-1

2 fr the area. In muntain cmmunities, it is imprtant t knw where the lcal weather statin is lcated s gardeners can factr in the difference in their specific lcatin t frecast temperatures mre accurately. Examples f factrs t cnsider include the fllwing: Elevatin A 300 ft rise in elevatin accunts fr apprximately 1 F drp in temperature. Drainage At night, cl air drains t lw spts. Valley flrs may be mre than 10 F cler than surrunding gardens n hillsides abve the valley flr. That is why fruit rchards are typically lcated n the benches rather than n the valley flr. Figure 1. This garden n the hillside abve Steambat Springs, Clrad (a muntain cmmunity with a shrt frst-free seasn) has gd drainage giving it a grwing seasn that is several weeks lnger than dwn in twn. Expsure Suthern expsures absrb mre slar radiatin than nrthern expsures. In muntain cmmunities, nrthern expsures will have shrter grwing seasns. In muntain cmmunities, gardeners ften place warm seasn plants, like tmates, n the suth side f buildings t capture mre heat. Based n lcal tpgraphy, buildings, fences, plantings and garden areas may be prtected frm r expsed t cld and drying winds. They may als be expsed t r prtected frm warm and drying winds. Figure 2. Temperatures and grwing seasn vary greatly based n expsure. A nrth facing expsure will typically be cler and mist. A suth facing expsures will typically be ht and dry. Thermal heat mass (surrunding rcks) In many Clrad cmmunities, the surrunding rck frmatins can frm heat sinks creating wnderful gardening spts fr lcal gardeners. Nestled in amng the muntains, sme gardeners have grwing seasns several weeks lnger than neighbrs nly a half mile away. In cler lcatins, rck mulch may give sme frst prtectin and increase temperatures fr enhanced crp grwth. In warmer lcatins, rck mulch can significantly increase summer temperatures and water 143-2

3 requirements f landscape plants. [Figure 3] In Phenix, Arizna, the urban heat island (with all the rck mulch instead f grass and trees) has significantly raised day and night temperatures. The upward cnvectin f heat has becme s strng that summer strms g arund the city and are nt raining n the urban heat island. Figure 3. The sidewalks and stne walls f this intercity plaza creates a heat pcket with a frst free perids three mnths lnger than the surrunding neighbrhd. Influence f Heat n Crp Grwth Temperature affects the grwth and prductivity f plants, depending n whether the plant is a warm seasn r cl seasn crp. Phtsynthesis Within limits, rates f phtsynthesis and respiratin bth rise with increasing temperatures. As temperatures reach the upper grwing limits fr the crp, the rate f fd used by respiratin may exceed the rate at which fd is manufactured by phtsynthesis. Fr tmates, grwth peaks at 96 F. Temperature influence n grwth Seeds f cl seasn crps germinate at 40 t 80. Warm seasn crp seeds germinate at 50 F t 90 F. In the spring, cl sil temperatures are a limiting factr fr plant grwth. In mid-summer, ht sil temperatures may prhibit seed germinatin. Examples f temperature influence n flwering Tmates Pllen des nt develp if night temperatures are belw 55 F. Blssms drp if daytime temperatures rise abve 95 F befre 10 a.m. Tmates grwn in cl climates will have sfter fruit with bland flavrs. Spinach (a cl seasn, shrt day crp) flwers in warm weather with lng days. Christmas cacti and pinsettias flwer in respnse t cl temperatures and shrt days

4 Examples f temperature influence n crp quality High temperatures increase respiratin rates, reducing sugar cntent f prduce. Fruits and vegetables grwn in heat will be less sweet. In heat, crp yields reduce while water demand ges up. In ht weather, flwer clrs fade and flwers have a shrter life. Table 1 illustrates temperature differences in warm seasn tmates and cl seasn cle crps. Table 1. Temperature Cmparisn f Cl Seasn and Warm Seasn Crps Cl Seasn: Warm Seasn: Temperature brccli, cabbage, and tmates, peppers, squash, fr cauliflwer and melns Germinatin 40 F t 90 F, 80 F ptimum 50 F t 100 F, 80 F ptimum Daytime Daytime 65 F t 80 F preferred 86 F ptimum 40 F minimum 60 F minimum Grwth Nighttime A week belw 55 F will >32 F, tender stunt plant, reducing transplants > mid-20s F, established yields Nighttime plants >52 F Flwering Sil Temperature extremes lead t blting and buttning. Cl Use rganic mulch t cl sil. Since seeds germinate best in warm sils, use transplants fr spring planting, and direct seeding fr mid-summer plantings (fall harvest). Nighttime <55 F, nnviable pllen (use blssm set hrmnes) Daytime >95 F by 10 a.m., blssms abrt Warm Use black plastic mulch t warm sil, increasing yields and earliness f crp. Heat Zne Map A new cncept in plant selectin is heat zne mapping, a measurement f the typical summer heat accumulatin. It will help identify gegraphic areas that have adequate heat accumulatin t mature varius crps. The American Hrticultural Sciety s Heat Zne Map can be viewed nline at: Heat znes can be srted by zip cdes. T lk up a heat zne by zip cde, g 143-4

5 nline at It shuld be recgnized that in muntain cmmunities, minr changes in elevatin and expsure (fr example, suth slpes versus nrth slpes) make significant differences in heat accumulatin. A heat zne fr a cmmunity s zip cde may nt reflect the actual grwing cnditins in any specific garden. Influence f Cld Temperatures Hardiness Zne Map Hardiness zne maps indicate the average annual minimum temperature expected fr gegraphic areas. While this is a factr in plant selectin, it is nly ne f many factrs influencing plant hardiness. In 2012, the U.S. Department f Agriculture released a new USDA Hardiness Zne Map. It can be fund at It dcuments a climate zne creep, that is znes mving nrthwards in recent years. Znes are based n a 10 F difference in average annual minimum temperature. Average Annual Minimum Temperature Zne 4 Zne 5 Zne 6-20 F t 30 F -10 F t 20 F 0 F t 10 F Mst f the Clrad Frnt Range area falls int Zne 5, with cl muntain areas in Zne 4. Warmer lcatins in the Denver Metr, Frt Cllins, El Pas, and Puebl Cunties fall int Zne 6. Warmer areas f western, suthwestern, and sutheastern Clrad are in Zne 6. Plant Hardiness Hardiness refers t a plant s tlerance t cld temperatures. Lw temperature is nly ne f many factrs influencing plant hardiness (ability t tlerate cld temperatures). Key hardiness factrs include the fllwing: [Figure 4] Phtperid Genetics (surce f plant material) Lw temperature Recent temperature pattern Rapid temperature changes Misture Wind expsure Sun expsure Carbhydrate reserve 143-5

6 Figure 4. Influence f temperature change n winter hardiness f trees The slid line represents a tree's hardiness. Regins A-D represents varius stages f hardiness thrugh the winter seasn. The dtted line represents temperature. When the dtted (temperature) line drps belw the slid (hardiness) line, damage ccurs. Pints 1-4 represent damage situatins. A. Increased cld hardiness induced by shrter day length f fall. B. Increased cld hardiness induced by lwering temperatures. C. Dehardening due t abnrmally warm mid-winter temperatures. D. Nrmal spring dehardening as temperatures warm. 1. Injury due t rapid drp in temperatures with inadequate fall hardening. 2. Injury at temperatures lwer than hardening capability. 3. Injury due t rise and fall f midwinter temperatures. 4. Injury due t spring frsts. Examples f Winter Injury Bud kill and dieback Frm spring and fall frsts Rt temperature injury Rts have limited tlerance t sub-freezing temperatures. Rts receive limited prtectin frm sil, mulch, and snw. Under extreme cld, rts may be killed by the lack f snw cver r mulch. Street trees are at high risk fr rt kill in extreme, lng-term cld. Sil heaving pushes ut plants, breaking rts. Prtect with snw cver r mulch. Trunk injury Drught predispses trunks t winter injury

7 Sunscald Caused by heating f bark n sunny winter days fllwed by a rapid temperature drp, rupturing membranes as cells freeze. Winter drught predispses tree trunks t sunscald. [Figure 5] Figure 5. Suthwest bark injury is cmmn n trees that are drught stressed, such as this tree with a restricted rt spread. Frst shake Separatin f wd alng ne r mre grwth rings, typically between phlem (inner bark) and xylem (wd), caused by sudden rise in bark temperature. Frst crack Vertical split n tree trunk caused by rapid drp in bark temperature. [Figure 6] Figure 6. Vertical frst crack is cmmn n trees when the temperature drps rapidly. In Clrad it is cmmn t g frm a nice spring day back t cld with a 40 t 60 degree temperature drp in an hur! Winter injury n evergreens Winter drught Water transpires frm needles and cannt be replaced frm frzen sils. It is mre severe n grwing tips and n the windy side f trees. [Figure 7] Sunscald Winter sun warms needles, fllwed by rapid temperature drp rupturing cell membranes. It ccurs typically n suthwest side, side f reflected heat, r with sudden shade. Pht-xidizatin f chlrphyll Fliage bleaches during cld sunny days. Needles may green-up again in spring. Tissue kill Tissues killed when temperatures drp belw hardiness levels. Figure 7. Winter drught, sunscald, and pht-xidizatin f chlrphyll are cmmn n arbrvitae. It s a pr plant chice fr this windy site with little winter misture

8 Rest Perid An accumulatin f cl units cntrls the flwering perid f temperate-zne wdy plants. The winter rest perid (hurs belw 45 F) required t break bud drmancy includes: Aprict hur Peach hurs Apple hurs Pear hurs Cherry, sur hurs Plum, Eurpean hurs Cherry, sweet hurs Plum, Japanese hurs Additinal Infrmatin CMG GardenNtes n Btany: #121 Hrticulture Classificatin Terms #136 Plant Structures: Fruit #122 Taxnmic Classificatin #137 Plant Structures: Seeds #131 Plant Structures: Cells, Tissues, #141 Plant Grwth Factrs: Phtsynthesis, and Structures Respiratin and Transpiratin #132 Plant Structures: Rts #142 Plant Grwth Factrs: Light #133 Plant Structures: Stems #143 Plant Grwth Factrs: Temperature #134 Plant Structures: Leaves #144 Plant Grwth Factrs: Water #135 Plant Structures: Flwers #145 Plant Grwth Factrs: Hrmnes Authr: David Whiting, Cnsumer Hrticulture Specialist (retired), Clrad State University Extensin. Phtgraphs and line drawing by David Whiting and Sctt Jhnsn; used by permissin. Clrad Master Gardener GardenNtes are available nline at Clrad State University, U.S. Department f Agriculture and Clrad cunties cperating. Extensin prgrams are available t all withut discriminatin. N endrsement f prducts mentined is intended nr is criticism implied f prducts nt mentined. Cpyright Clrad State University Extensin. All Rights Reserved. CMG GardenNtes may be reprduced, withut change r additins, fr nnprfit educatinal use. Revised July