ebook - gardening - short-season vegetable gardening

8/14/2019 eBook - Gardening - Short-Season Vegetable Gardening

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PNW 497

A Pacific Northwest Extension Publication

University of Idaho Oregon State University Washington State University

Introduction

acific Northwest gardeners may find thegrowing season where they live too short to

grow certain vegetables. Air and soil tempera-tures may be lower than optimal for plant

growth. Untimely frosts or snow, combined withlow humidity and excessive wind, make it neces-sary for the home gardener to use special prac-tices to get the best production. The techniquesoutlined in this publication will be essential togrow most vegetable crops.

To successfully grow vegetables in short seasonareas, you will need to become a weatherwatcher. Information is available on weatherradios, cable TV stations, and local newspapers.These should be monitored to anticipate adverseweather conditions such as local frosts. Equipyour garden with an accurate high and lowtemperature recording thermometer to chartdaily extremes. Obtain a number of high quality,dial type soil thermometers. Place the thermom-eter probes in your garden soil at rooting depth.The temperature of your soil will indicate whatseeds and plants can be planted, and how muchheat is available under plastic mulches and plantcovers.

In order to get started in vegetable production,determine the length of your frost-free growingseason. It can be as short as 21 days. Remember,the growing season may be 20 percent shorter or

longer than average, and some years are betterthan others. Dont let conventional local wisdomdiscourage your gardening adventures but realizethat local experience is useful in defining whatspossible. (See EXP 494, Spring and Fall FreezingTemperatures and Growing Seasons in Idahoand CIS 844, Frost Protection for the HomeGardener.)

PChoose the warmest spot possible

for your garden.

Choosing the best garden site is critical for suc-cess in vegetable gardening in areas with shortseasons and cool climates. Even a small change intemperature can make a difference during springand fall frosts. Garden site selection affects windexposure, temperature, and humidity. Windremoves heat radiating from the soil, dries outplants, and causes plants to close their stomates(tiny leaf openings) to conserve water, thusreducing growth potential. Humidity can raisethe temperature slightly by acting as a heat sinkaround plants.

The garden site should be in an area that receivesfull sun and provides protection from the windwindbreaks such as vegetation or buildings. The

south-facing side of a building or wall is ideal, asthe site will receive reflected light and heat. Agentle south or southeast slope with good airdrainage will warm early in the spring and willnot be a frost pocket. Avoid low-lying areaswhere cold air accumulates. Orient plant rowsnorth to south to maximize sun interception overthe entire leaf canopy. Light, sandy loam soilwarms faster than heavy clay soils. (See CIS 755,Planning and Preparing the Vegetable GardenSite, and EC 871, Planning a Home or FarmVegetable Garden.)

Prepare the soil carefully.Short season gardeners must have the best soilpossible in order to develop crops quickly. Wet,clay soil stays cold late into the spring. A light,sandy loam is ideal. Amending soil becomesimportant if it has too much clay or sand, or if itis compacted. Adding organic matter will loosen

Short SeasonVegetable Gardening

Jo Ann Robbins and Wm. Michael Colt


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clay and compacted soil, and increase wa terretention and fertility in a gravelly, or sand y soil.

Tilling w et soil resu lts in comp action and de-struction of structure texture. In the spring, letyour soil dry before tilling, or p repare yourgarden soils in the fall when conditions are dry.Organic matter, incorporated in the fall, such ascompost, will be available for breakdow n w henspring tem peratu res rise. Fall soil prep aration

will allow the short season gard ener to plantearlier in the spring.

Beds raised 10 to 12 inches above the norm al soillevel have m any ad vantages in short seasonareas. Soil in raised beds dr ies out and w arm sfaster in the spr ing, and d rainage is betterthrou ghou t the season, allowing for earlierplanting an d better p lant grow th. Soil in raisedbeds with a southern exposure w ill warm morethan level soil (Figure 1). Add n ew soil, or amendnative soil, du ring the formation of the beds.Make beds 3 to 4 feet wide so you can work from

the pa thw ays on either side, eliminating compac-

plastic, with a sm all, insulating airspace betw eenthe layers, will prod uce even higher soil tempera-tures.

Black plastic is not as effective as clear p lastic inwar ming the soil and results in higher temp era-tures only w hen in contact with the soil.

Wavelength selective p lastic film, wh ich allowsheat waves to penetrate the film, but keeps light

rays from enter ing, will also warm soil effectivelyin early spring. This type of material (marketedas infrared transmitting (IRT) plastic or u nd erbrand initials Al-Or) is used from early springthrough th e grow ing season. (See the section onperm anent m ulches for more details in workingwith plastic film mulch.)

Foster optimum fertility.

Vegetables planted in short season areas mu sthave ad equate sup plies of plant nutrients (espe-cially nitrogen) for optimal grow th. Plants mu st

get off to a fast start and su stain continued goodgrowth to matu re qu ickly. A soil test prior toplanting is useful to determine the pH of yoursoil and wh at levels of nitrogen, phosph orous,and potassium are needed for best growth.

Organic fertilizers requ ire warm soils to prom otemaximum release of nu trients. The warm er thesoil, the faster the microbes can break d ownorganic sources of nu trients to make them avail-able over a p eriod of time. In colder soils, theseorganic nutrients m ay be available too slowly.Sup plemental soluble inorgan ic fertilizer may

help p romote the rapid grow th needed.Solub le fertilizers work well for plan ts in coldsoils because the nu trients are imm ediately

available. Dissolve these in water and app ly oradd to soil in d ry, granular form. Apply acomplete fertilizer high in ph osphorou s atplanting time either in a band adjacent to therow or as a water solution. Add n itro-gen later dry or as a w ater-applied

tion from foot tra ffic. (See EC 1228, Planningand Preparing Your Vegetable Garden Site, andNCFS 270, Raised Bed Gardening.)

Warm the soil early.

To provide w arm soil early in the spring, coverthe bare ground with clear polyethylene plasticfilm. The plastic retains the suns warm th an dwill often raise the soil temperatu re 10 to 15degrees in a few days. A dou ble layer of clear

South

South

Figure 1.


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fertilizer. Several app lications of nitrogen overthe grow ing season, or fertilizing with a slowrelease material, will ensure a steady sup ply ofnu trients. (See CIS 922, Fertilizing Gardens; FG0050, Fertilizer Gu ide: Vegetable and FlowerGardens, Except Irrigated Central Washington;and FG 0052, Fertilizer Gu ide: Hom e VegetableGardens, Irrigated Central Washington.)

Choose cool seasonadapted vegetables.

Cool season vegetables seeds can germinate insoil that is 40F or cooler. They are also ab le togrow and mature w hen exposed to at cooler dayand night tempera tures. Most and can resistsome frost and light freezes. Vegetables that willgerminate at 40F includ e: fava bean s, beets,broccoli, brussels sprou ts, Chinese cabbage,cabbage, carrots, cau liflower , kale, collards,kohlrabi, leeks, parsley, peas, radish, ru tabaga,

Swiss chard, celery, and turnips. Lettuce, onion,par snip, and sp inach will germinate at 35F.Direct plant ing of these crops is possible in mostgrowing areas. How ever, when the growingseason is shor t (less than 90 days) and cold soilspersist, season-extend ing cultural techniquesmay be necessary to matur e even these crops.Techniques include soil warm ing, growing orpu rchasing transplants, pre-germination of seeds,plastic mu lches, and plant covers.

Of the cool season crops, beets, carro ts, andonions will grow w ell in warm er temperatu res,but the others will form seed stalks or produ celower yields w ith inferior flavor when planteddu ring warm er temperatures. Crops like Chinesecabbage and celery may also produce seed stalksif exposed to cool spring tem peratu res un lessvarieties resistant to flowering and seeding areused.

Crops requ iring 50F or higher soil temperatu resfor seed germination w ill need to be startedindoors and transp lanted after the soil and airtemperatures warm, or directly sowed at thattime. Examples of such crops are: corn, tomatoes,

green beans, dry beans, cucum bers, squash,pu mp kin, eggplant, melons, cantaloupe, okra,and pep pers. Season-extend ing cultural tech-niques w ill be necessary to realize a harvest ofsome of these crops in areas where the grow ingseason is less than about 120 days. These warmseason crops will need p rotection because theywill not withstand any frosts, and cold n ightswill slow their grow th. (See PNW 170, Propagat-

ing Plants from Seed.)

Choose early maturing vegetables

and cultivars.

The use of early matu ring crops is another im-portan t factor for short season vegetable garden-ers. Cool season crops such as sp inach, radishes,lettuce, and kohlrabi are generally able to reach astage where they can be harvested in less than 60days. Of those requiring 60 to 90 days, peas,broccoli, beets, carrots, onions, cabbage, and

cauliflower can all be planted du ring fairly coolweather. With corn and bu sh beans, however, theshort season gardener w ill need to use season-extending cultural techniques. These techniqueswill become essential with crops requ iring m orethan 90 days for maturity such as most toma toes,pepp ers, eggplant, melons, squashes, and pu mp -kins. Not only do these crops requ ire a greaterlength of time to reach an acceptable harveststage, but they also must have w armer temp era-tures to grow.

Within each crop type, choice of cultivar iscritical for the short season gardener. Chooseearly cultivars w ith the shortest days fromplanting to matu rity. Even a few d ays can meanthe d ifference between a h arvestable crop or nocrop at all. For example, corn cultivars va ry from53 to 112 days in the num ber of days to harvest.Choose cultivars for northern gard ens or coldclimates. These grow and prod uce qu ickly. Lookfor num ber of days to matu rity on the seedpacket or in the catalog. (See PNW 45, Choosingand Using Western Vegetables.)


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Buy your seeds from local garden centers or seedoutlets. In short season areas, they w ill carryseason-approp riate crops and cultivars. Be sureto read the length of growing season on eachpacket before pu rchase. Seed catalogs have awid e choice of cultivars, and compan ies in thenorthern states and Canad a are likely to havecultivars that are specific for short grow ingseason needs. Obtain sources from garden maga-

zines, or from your nearest Cooperative Exten-sion office.

Start plants inside

to get a jump on the season.

To prod uce some warm season crops in shortseason areas start vegetable plants indoors andtransplant them to the garden. You can pu rchasetransplants or grow you r own. Growing yourown tr ansp lants allows you to choose amongmore cultivars, and you can provid e healthy

plants of the desired size for transplanting.Research show the older the transplant, the betterthey w ill resistance to cold weather . it will have.Younger plants will take abuse and poor grow ingconditions better, but are m ore susceptible tofrost damage.

Hard en transplants by gradual exposure tooutd oor conditions for seven to ten days toslowly acclimate seedlings to the ou tdoors beforetransp lanting. Gradually expose the plants to acooler environmen t with m ore light and lesswater. You can harden warm season vegetablesso they can better resist exposu re to aga inst full

sun, wind-whipp ing, and dry soil, but not tofrost. Transp lant on a cloud y day or in theevening to lessen the shock. Do not set tall plantsany d eeper than necessary. To avoid p lacing theroots in cold soil, lay them in shallow trencheswith leaves turned up above the soil. Pepp ersand tomatoes are par ticularly suited to thispractice. (See CIS 800, Growing VegetableSeedlings for Transplanting.)

Soak or pre-germinate seeds.

Germination can be accelerated a few d ays bysoaking seeds of squash and other cucurbits inwater overnight and planting w hile still moist.This approach also avoids a cold sensitive stagein early seed germination. This method is not ashelpful for seed such as beans and peas thatswell and germinate rapidly.

There is an ad vantage from p re-germination ofthe seed of m ost vegetables. Do this by keepingseeds w arm and dam p in a wet pap er or clothtowel. When the new growth is 1/ 4-inch long,plant the seeds without allowing them to dry. Adelay in planting, because of bad w eather, maycause seedlings to grow too big to hand le. If thereis a delay in planting, refrigerate the seedlings fora short time at a tem peratu re above freezing. Thismethod can save up to two w eeks for slowgerminating crops such as parsley and carrot.


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Use a permanent mulch, after the

soil has warmed.

Most mu lches w ill conserve moisture, p rotect soilfrom erosion, and red uce weed growth. They canalso moderate soil temp eratures and affect thenitrogen level in the sur face layers of the soil.Short season gard eners w ill want to choose a

growing season mulch that maintains or in-creases soil temperatu res, and d oes not reducethe n itrogen level in the soil.

Probably the best m ulch is a clear plastic mulch,wh ich, in the early sp ring, is the best soil warmer.Remove clear plastic mulch when you plant seedor tran splants. Planting can also be accomplishedthrou gh h oles and slits in the plastic. If the p lasticis left in place, weeds m ay grow under it. Blackplastic mu lch w ill prevent the grow th of weeds,but d oes not warm the soil as mu ch as clearplastic, especially if it is not in good contact withthe soil. Clear mu lch can be rep laced with blackplastic at the time of p lanting to get the benefitsof both.

Wavelength selective plastic film, which allowsheat w aves to penetra te the soil, but keeps lightrays from entering, will both warm the soil andkeep w eeds from growing. This type of mu lchcan be left in p lace all summ er.

Plastic film mu lches serve as barr iers to fru it rotand soilborne diseases by provid ing a soil freesurface for vegetables. They also reduce leaching

from rainfall and keep mobile fertilizer nu trientsfrom being lost from the root zone. If treated w ithcare, some th icker p lastics can be used for morethan one grow ing season. Disposal of largeamou nts of plastic can be a problem. A d ripirrigation system installed over or un der p lasticmu lch p rovides a very efficient and low mainte-nance method for growing vegetables.

Organic mu lches generally modera te soil tem-

peratu re. Most, if presen t on cold soil, will keepthe soil from w arm ing as fast as bare soil, keep-ing soil cold longer into the spring. This is espe-cially true of light colored m ulches, wh ich reflectthe sun s rays. Short season gard eners shou ldonly app ly dark colored mu lches, such as com-post, after the soil has warm ed. An ap plication ofdar k colored m ulch to warm soil in the latesum mer w ill help m aintain a warm er soil laterinto the fall.

Organ ic mu lches decompose on th e soil surface,adding va luable plant nu trients to the soil. This is

especially true w ith materials high in nitrogensuch as vetch clipp ings. Very w oody m ulches,such as sawdust, when incorpora ted into the soil,will use soil nitrogen du ring decomp osition,redu cing th e levels available to vegetable p lants.To avoid th is problem, do n ot incorporate w oodyorganic mulches un til after harvest. Add ition ofextra nitrogen to the soil at that time w ill enhancebreakdown . It may be best to comp ost thesematerials prior to using them as mu lch.

Clear fiberglassClear plastic

Figure 2.


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One d isadvantage of any type of mu lch to a shortseason gardener is the redu ction of nighttimeheat radiated from warm soil into the surround -ing air. This radiated h eat, dur ing spring or fallfrosts, can be the d ifference between a frozenplant and one that is untouched by the cold.Placing a cover over a p lant on a th ickly mu lchedarea m ay not afford m uch extra frost protection.(See CIS 837, Mu lches for the Home Landscape

and Garden, and EC 1247, Gardening w ithComp osts, Mulches, and Row Covers.)

Use covers or screens

to protect plants.

Covering plants modifies the temp erature, wind ,and humidity. Air and soil temperatu res arewarmer an d the cover will conserve heat radi-ated from the soil during the night. A smallincrease in temperatu re has a large effect, be-

cause many p lant growth reactions double theirrate for every 18F. In short season areas, cover-ing plants in the spring and th e fall extends thewarm season. Keeping covers in p lace du ring thewh ole season m ay be necessary in particularlycool areas.

Some p rotectors are large enou gh to cover sev-eral plants or row s of plants, similar to having agreenhouses with no foundation over tendergarden crops (Figure 2). Cold frames have h ingedcovers that can be removed or propped op endu ring the day. A light frame covered w ith

plastic in an A shap e (Figure 2) can be p lacedover one or several rows and left in place thewh ole growing season. Plant tall crops in themidd le and low ones near the sides. A sheet offiberglass arched over a row makes a tunnelleaving the end s open for ventilation (Figure 2).Clear plastic stretched over hoops provides thesame effect. Floating row covers of spun polyes-ter ma terial can also be u sed to cover vegetables.The light m aterial rests directly on the plants.These materials also will reduce insect dam ageby excluding the pests.

Small protectors, such as hotcaps of p artiallytranspa rent waxed p aper, can be used for one ortwo plan ts (Figure 3). Emp ty p lastic gallon jugswith the bottoms removed can be placed oversmall plan ts. Clear plastic fences or screensplaced aroun d one or several plants give thesame effect, but the open top w ill need to becovered on cold nights. Small plant covers(cloches) made of panes of glass or plastic held

by a w ire clamp have been u sed for many yearsin England . Old tires can provide w ind p rotec-tion for single plants p lanted inside and willabsorb the suns warmth. When filled w ith water,the wa ter will hold heat for release du ring thenight (Figure 3). Comm ercial plant covers withvertical tubes of water tha t store heat for releaseat night are ideal for individu al plants.

Any covering method exclud es bees, so uncoverplants periodically for pollination. All coveringsystems need to provide ventilation to preven toverheating du ring warm days. A single layer ofplastic or glass is a p oor insulating m aterial, socover with blankets, sheets, canvas, or bur lap

6" x 6" wireWith plastic cover

Stake framewith plastic cover

Plastic jug withbottom removed

Figure 3.

Hot cap(cut-away view)

Tire


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sacks filled w ith straw to insulate the structureson cold nights.

Only the imagination and ingenu ity of the gar-den er limit types an d varieties of coveringmethod s. For example, clear p lastic stretchedover the top of vegetables planted in a furrowwill trap the suns heat in the air and soil of thetrench to speed the early grow th (Figure 4). Later,slit the p lastic over the row to prevent overheat-

ing. You m ay need to pu ll the leaves of the plantsup through the slit.

Add heat to any of the above covering systemsby burying heat tape in the soil, extending thegrowing season even longer. Planting vegetablesinto soil covering d ecomposing compost orman ure piles and u sing any of the plant coversdiscussed w ill also provid e extra heat for growth.

Water stores the suns heat well. A simple tech-nique is to half bury a gallon jug of wa ter neareach p lant. During sunny days, water will warmand release the heat to the soil and the air nearthe plant during cool nights (Figure 5). Water-filled p lastic bags, metal cans, or containers canbe used in the same way. Heavy solid m aterialssuch as bricks, concrete blocks, and rocks willalso absorb the sun s heat an d release it later.

Includ e a storing d evice inside plant covers tostore solar heat for release du ring the night. Blackcontainers and m aterials will absorb m ore heatthan light-colored ones.

Windscreens and light reflectors used ind ividu -ally or in combination are u seful to keep w indaway from plants and to concentrate the sunslight and heat. An effective combination is avertical screen along each row on the side tow ard

the pr evailing wind . If this is on the north side ofthe row , cover the screen with reflective materialsuch as alum inum foil to reflect the suns raystoward the crop. Shingles or boards set in theground near small, newly transplanted plantswill provide wind and sun p rotection. (See NCFS246, Constructing Cold Frames and Hotbed s.)

The techniques outlined in this pu blication canhelp the gard ener meet the short season chal-lenge and grow a variety of healthy homegrownvegetables. Accept the limitations of the climate,choose crops and var ieties carefully, and select

the season-extending p ractices that fit you r life-style.

About the authors

JoAnn Robbins is an Extension Educator andHorticultu rist at UIs Blaine County ExtensionOffice. Wm. Michael Colt, is Extension Horticul-tur ist at UIs Parm a R&E Center.

Clear plastic covers

Water jug

Figure 5.

Water in heavy plastic tubor old innertube

Stone circle

Figure 4.


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Published December 1996. Reprinted November 2000 $2.00

Pacific Northwest Extension publications are jointly produced by the three Pacific Northwest statesIdaho, Oregon, andWashington. Similar crops, climate, and topography create a natural geographic unit that crosses state lines. Since 1949, thePNW program has published more than 400 titles. Joint writing, editing, and production have prevented duplication of effort,

broadened the availability of faculty specialists, and substantially reduced costs for the participating states.

Published and distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914, by the University of IdahoCooperative Extension System, the Oregon State University Extension Service, Washington State University CooperativeExtension, and the U.S. Department of Agriculture cooperating.

The three participating Extension services provide equal opportunity in education and employment on the basis of race, color,religion, national origin, gender, age, disability, or status as a Vietnam-era veteran as required by state and federal laws.The University of Idaho Cooperative Extension System, Oregon State University Extension Service, and Washington StateUniversity Cooperative Extension are Equal Opportunity Employers.

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