CMG GardenNotes #723 Growing Vegetables in a Hobby Greenhouse

Transcription

1 CMG GardenNtes #723 Grwing Vegetables in a Hbby Greenhuse Outline: Extending the grwing seasn, page 1 Passive slar greenhuse, page 1 Cl seasn vegetables, page 3 Warm seasn vegetables, page 5 Hbby greenhuse references, page 6 Extending the Grwing Seasn Off-seasn vegetable prductin in the hbby slar greenhuse is an enjyable way fr year-rund gardeners t extend the harvest seasn f fresh vegetables. Hwever, withut the expense f a greenhuse, gardener can extend the grwing seasn weeks t even mnths with cld frames and plastic tunnel gardening. Fr details n frst prtect and cld frames, refer the CMG GardenNtes #722, Frst Prtect and Extending the Grwing Seasn. Winter vegetable prductin in a greenhuse is nly cst effective with an energy efficient greenhuse structure, a well-designed slar cllectr, and ptimum management. Winter vegetables have a slw grwth rate due t lw light intensity. Crps shuld be planted t btain a near harvestable size by mid- Octber. The use f artificial light fr vegetable prductin (except fr starting transplants) is generally nt cst effective. A gardener s success is dependent n the greenhuse design and cnstructin t cnserve energy and n the management care given the greenhuse crps. Befre investing in a greenhuse, carefully cnsider yur real interests in extending the gardening seasn. Are yu nly interested in adding a few weeks t the harvest seasn? Are yu interested in year-rund gardening in a slar greenhuse OR d yu need a winter break? Passive Slar Greenhuse Fr the gardener cnsidering a passive slar hbby greenhuse, here are a few key pints t cnsider. Refer t ther greenhuse references fr additinal details

2 Fr slar cllectrs, any area with direct sun, but nt blcking slar illuminatin f plants, is a ptential lcatin. Fr a hbby greenhuse, slar cllectrs are typically built int an insulated nrth wall. A slid brick wall n the nrth makes a gd slar cllectr. Brick absrbs 30 t 35% f the slar radiatin. With a brick strage wall, the greenhuse quickly heats n a sunny winter day and ventilatin will be needed by mid mrning. [Figure 1] Figure 1. Brick strage wall in passive slar hbby greenhuse Thermal strage mass is a wall made with tw layers f brick filled with cncrete. In this well-built structure, nighttime temperatures drpped t 35 F with n supplemental heat when utside temperatures drpped t -17 F. Nte yung crps in raised-bed style garden with drip irrigatin. Water strage using plastic milk jugs makes a great strage system. Water jugs absrb 90% f the slar radiatin, hlding three times mre heat than brick r rck. This increased heat strage hlds night temperature higher lnger int the night, resulting in slightly imprved crp grwth cmpared t brick strage. [Figure 2] Figure 2. Milk jug water strage wall in a passive slar hbby greenhuse. Dispsable milk jugs n left and returnable milk jugs n right are spray painted flat black. In this well-built structure, nighttime temperatures drpped t 39 F with n supplemental heat when utside temperatures drpped t -17 F. With milk jug strage, spray the milk jugs with flat black paint, and add ne tablespn f liquid bleach per jug (t prevent algae grwth in the warm water). Secure the cap back n the jug with a ring f caulk. Place the milk jug n a bkcase type frame nt mre than tw jugs high. Dispsable milk jugs develp leaks ver time and require rutine replacement. Heavier weight jugs (like returnable plastic milk jugs) last lnger. Other types f cntainers may be used. Keep the size tw gallns r smaller r water will stratify with ht water n the tp and cler water n the bttm, reducing efficiency

3 A passive slar hbby greenhuse is nly effective when built t ptimum energy specificatins. Because the majr heat lss is thrugh the glazing, duble-glazing (which reduces heat lss by 25 t 35%) is required. Duble glazed pati dr glass is great fr glazing a hbby greenhuse. Glass suppliers smetimes have recycled (used) pati dr glass available at minimal prices. Night curtains may add an additinal 30 t 50% energy cnservatin. On a passive slar hbby greenhuse, the nrth, east, and west walls are typically insulated t an R-value f R38. The fundatin and flr are insulated frm heat lss t the grund. [Figure 3] Figure 3. Hbby greenhuse being cnstructed with duble glazed pati dr glass. Cld air infiltratin is the secnd majr surce f heat lss. Fr passive slar t be effective, minimize cld air infiltratin with gd design and cnstructin techniques. Insulative vent cvers help reduce cld air infiltratin at night, but must be remved daily t allw thermstats t maintain prper temperature. A passive slar hbby greenhuse requires an east t west rientatin. In nrthern Clrad latitudes, an east t west rientatin receives 25% mre slar energy than a nrth t suth rientatin. Smetimes the hbby greenhuse may be riented slightly t the east fr faster mrning warming. An rientatin 20º ff east t west will cut 4 t 5% f the slar ptential, while an rientatin 45º ff east t west will cut 18 t 20% f the slar ptential. At nrthern Clrad latitudes in January, a nrth t suth rientatin cuts 25% f the slar ptential. A prly cnstructed greenhuse cannt be retrfitted int an efficient passive slar unit. Cl Seasn Vegetables Cl seasn vegetables d well in the greenhuse r cld frame. High temperatures are nt desirable, and an ccasinal near freezing dip will nt harm crps. High light intensity is nt as critical fr cl seasn crps as fr warm seasn crps. [Figure 3] Figure 4. Lettuce in slar greenhuse raised bed

4 General temperatures fr cl seasn crps Daytime: 50ºF t 70ºF Shrt-term temperature extremes: 35ºF t 90ºF Nighttime: 45 ºF t 55 ºF Germinatin: 40ºF t 75ºF Minimum Minimum Equal- Cntainer Distance Vegetable Size* Spacing Remarks Beets 8 deep 6 Grw in fall and hld in cl greenhuse fr winter use. Prperly thin. Brccli 10 deep 18 High yield fr space used. Cabbage 5 gallns/plant Avid lng-term temperature extremes. Cauliflwer Heads split with warm humid cnditins. Carrts 12 deep 3 Extremely sweet with adequate water and cl temperatures. Use shrt varieties, like Shrt & Sweet r Scarlet Nantes Questinable use f greenhuse space. Chard 8 deep 9-12 Des exceptinally well. Khlrabi 8 deep 9 Des exceptinally well. Leaf lettuce 4 deep 9 Easy t grw in fall, winter and spring in slar greenhuse. Use sfthead r leaf types. Keep temperatures under 70 ºF. Green nins 6 deep 3 Never let nins get dry. Sensitive t phtperid (length f night). With shrt days (lng nights), grwth ges int leaf prductin. With lng days (12-16 hurs) energy ges int bulb prductin. Peas 8 deep 6 Use dwarf, edible-pd r snap types fr salads and stir-fry. Avid temperature extremes. Questinable use f space. D nt transplant well, nt well suited t cntainer gardening. Radish 5 deep 2-3 Avid water and heat stress. Must have 12 hurs f light t rt. Fr fall and spring crps in greenhuse. Spinach 8 deep 6 Needs cl greenhuse (45ºF t 50ºF) fr best quality. Avid temperature fluctuatins. Turnips 8 deep 6 Gd fr fall and spring crps. Many riental vegetables are als suited fr greenhuse prductin. *A larger cntainer size will make crp easier t care fr, prviding a larger supply f water and nutrients

5 Warm Seasn Vegetables Warm seasn vegetables require high light intensity and mderate night temperatures. They cannt be cst effectively grwn during the winter in a hbby greenhuse withut slar heat cllectrs. Greenhuse climates cntrl is critical fr these fruiting crps t prduce. Warm seasn crps are nt cmpatible with cl seasn crps due t differing temperature needs. General temperatures fr warm seasn crps Daytime 60ºF t 85ºF Shrt-term temperature extremes 50ºF t 95ºF Nighttime 55ºF t 65ºF Germinatin 60ºF t 85ºF Minimum Minimum Equal- Cntainer Distance Vegetable Size Spacing Remarks Beans 8 deep 6 Nt a cmmn greenhuse crp. Gd prductin with adequate light and spacing in spring and fall. Pr winter prductin. May be questinable use f greenhuse space. Cucumbers 8 deep 18 Requires high humidity, high light intensity, and gd misture. 3-4 gallns/plant Needs 75ºF t 80ºF day temperatures and 50ºF minimum nights. Avid temperature fluctuatins greater than 20ºF. Pr mid-winter prductin. Plant gynecius greenhuse types. Needs gd air circulatin t minimize pwdery mildew. Eggplant 8 deep 24 Hand pllinatin required. 4-5 gallns/plant Muskmeln 8 deep 24 Uses lts f space fr yield, try trellising. 5 gallns/plant Needs 80ºF day temperatures. Requires hand pllinatin. Needs gd air circulatin t minimize pwdery mildew. Peppers 8 deep 15 Minimum night temperatures f 55ºF. 2-5 gallns/plants Hand pllinatin required. Summer 8 deep 24 Hand pllinatin required. Squash 5 gallns/plant Needs gd air circulatin t minimize pwdery mildew. Prductive with gd sunshine. Tmates 12 deep 24 Minimum night temperature f 55 F. 2-5 gallns/plant Hand pllinatin required. (depending n cultivar/plant size) Prductive with gd sunshine. *A larger cntainer size will make crp easier t care fr, prviding a larger supply f water and nutrients

6 Figure 5. Beans in slar greenhuse raised bed Figure 6. Raised bed in slar greenhuse. Hbby Greenhuse References Greenhuses fr Hmewners and Gardeners. NRAES. Crnell University Cperative Extensin. 152 Riley-Rbb Hall. Ithaca, NY Phne Hw t Build and Operate Yur Greenhuse by Charles Ellwd. HP Bks Slar Greenhuses fr the Hme. Cperative Extensin, Crnell University, Ithaca, NY Slar Grwing Frame. Rdale Press The Slar Greenhuse Bk by James McCullagh. Rdale Press Authrs: David Whiting (CSU Extensin, retired), with Carl O Meara (CSU Extensin, Bulder Cunty), and Carl Wilsn (CSU Extensin, retired). Phtgraphs by David Whiting; used by permissin. CMG GardenNtes are available nline at Clrad Master Gardener training is made pssible, in part, by a grant frm the Clrad Garden Shw, Inc. 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 Octber