Growing Strawberries - Under Cover Practices PDF Print E-mail

INTRODUCTION:

Strawberries are a tricky crop, mainly because of its historical genetic development which dictates its requirements for successful plant development and high production.

SB developed from a genome that adapted itself to certain climatic conditions in the Northern hemisphere which forced it genetic evolution to sustain cold winters and to transform into fully mature and productive plant in short time spell, to reach its peak production when temperatures are still moderate and produce runners (Vegetative reproduction) when temperature are not suitable and support fruit production. The cold winter and short day light forcing the plant to dormancy , a phase vital for its recovery in spring since new crowns are formed during the dormancy stage.

SB is a crop in demand around the world with annual consumption estimated to be at about 7 billion pounds produced around the globe in 75 or more countries.

In South Africa it is a growing market. Due to its climatic diversity SB are grown in most of the coast line areas but not only and in fact are commercially grown in Gauteng area where the extreme temperature variations between Summer/Winter is a major issue.

 

 

 

 

 

 

 

STRAWBERRIES - GROWING PRACTICE IN OPEN FIELD.

Growing SB in open field is a practice used for last 100 years or so, using raised beds in suitable soil. SB strives in light soils and required constant irrigation due to its shallow root system. The main challenge is to overcome the short days, cold period of winter without extensive damages to the plant. Some growers using plastic mulch some using straw to cover the beds.

In Australia, Israel and other SB large producer’s countries the usage of low tunnels is a practice proven highly successful since plants under that cover conditions developed early then mulch cover and as temperatures raised in late winter plants are in full production. Low tunnels required certain structure to allow opening and closing mechanism for sufficient ventilation and reduce over heating later in spring.

Low tunnels are a permanent feature that used to keep soil temperature during the cold period or protect crop during heavy rains and hail storms.

The usage of frost protecting layer sheet during cold months is sometimes causing more demerges. If stretched properly while leaving a space of air layer between the sheet and the plant it can work but it is not an easy task to achieve. The sheet layer on the plants tops will keep pushing downwards creating a contact between the sheet and the leaves and sprouting crowns, causing them to freeze and rot.

STRAWBERRIES IN HYDROPONICS

Hydroponics methods are used to cultivate SB successfully during the last 3o years or so.

Using hydroponics method constitutes immediate challenges:

The Strawberry Plant root system – SB have a shallow root system highly sensitive to water logged media or to fast drying media.

The production per space- Since the need is to produce large quantities of fruit preferably in “out of season” required increase of plant density without compromising the fruit quality.

Light distribution- SB is a plant that produces its best in optimal conditions; correct temperature range and enough light. If one of this parameter not in place plant become stunned and total yield per plant will be reduced significantly.

Logistical issues- Handling the plants, harvesting, packing, spraying etc required easy access to the plant /s growing space.

Hydroponic growing methods using under cover protection provide at least theoretically the answer for temperature control but not always necessarily the light distribution.

Since the need of a grower is to produce marketable quantities in considerable short or medium long production season, plants density is pushed to the maximum. In experiments concluded around the world in comparing densities of 11 to 22 plants per sq/m all conclusively show that higher the density less quality marketable fruit is produced and overall fruit weight and fruit per plant remain averagely the same. One of the main reasons affecting the overall plant production and development relates to light distribution in the tunnel. Plants on the shade side will under develop in comparison to fully exposed plants on the sunny side.

The infrastructure used to accommodate various methods is costly; Gutter (troughs) system in various combinations sorting out in a way the Logistical aspects, while providing ample space between the rows and using heights as a space to increase density. This method is very practical logistically since most crop production is easily accessible. The main downfall is the need to replace the plants and handling the structure between crops. Gutter system in various experiments proved that light distribution and temperatures variation between plants on both sides of the gutter is a challenge and if gutters are not placed facing sun at high noon time across the tunnel length will affect productivity by up to 40%.

Bag culture is another used option which increases the need for intense labor since most plant handling is done on the ground floor. That system reduces dramatically plant density and commercially can be hardly considered viable.

Another options which start making impact is stakes towers (Vertical ); The method was experimented in various techniques and applications aiming to overcome the other methods deficiencies. The biggest challenge was to create an optimum density that justifying its commercial viability, to ensure fair light distribution amongst the plants, to provide easy accessibility to plants and easy fruit picking.

Since it is well recorded that SB plant root system in hydroponics culture can do well in volume of about 9-10 Litter space, the stakes system allow sufficient root space in a pot designed with 6 lobs. Each lob volume approximately 9 litters, but access roots if required can developed vertically inwards the pot centre. The stakes are laid one of the top of the other to 8 pots height allowing 48 plants on one stakes tower. Having a structure like that will not overcome the light distribution problem if kept stationary. Easygrow system equipped to rotate around its centre allowing plants to enjoy equal light exposure during the growing season. It also enjoy more efficient irrigation dripping from the top using gravitations to distribute water and nutrients across the growing space. The plants are easily accessible and fruit picking become less complicated. The systems using vertical growing method in various designs failed mainly on the basis of light distribution and sustainability of the structure. The system developed by Easygrow (http://www.easygrow.co.za/) effectively overcome those issues. (Easygrow also provide low tunnel solutions)

STRAWBERRIES and GROWING MEDIA

Another major issue in growing SB in Hydroponics is the effect of the growing media on plants development and production. Since SB plant root system is highly sensitive to over logged media but easily collapse when it’s to quickly drying-out, the media combination should allowed constant sufficient moisture but letting access water to run out of the system easily.

The combination of Coir and Perlite provides the exact balance required to sustain healthy root zone.

The mixture percentage between the two media is a result of certain considerations; the variety of SB used, the irrigation system used and obviously the growing structure itself. In general; any mixture up to 50% Coir, 50% perlite will serve as effective solution. If climatic conditions dictates’ very high temperatures in mid growing season more Coir and less Perlite in the mixture will be good enough to obtain root zone constant moisture ( 70%-30% ).

Coir as a growing media vary in quality and texture, it is therefore important to use fine coir which has less fiber content. The Perlite of Medium grade working well with coir but Coarse Perlite will act the same especially when coir particles are fine. SB can be grown effectively in Perlite on its own (Fine, medium or Coarse) but will required strict irrigation program to allow its full potential as a sole media ( SB shallow roots must be moist at all time).

The aim of SB grower is to produce quality marketable fruit , to keep production going longer as possible while reducing cost associated with maintenance ., labor and logistics. The article above does not deal with the importance of the SB varieties which affect the marketing timing. The principles described here intend to give a broad overlook on what and how to improve growing technique and to better production while considering the basic SB plant requirement.

 

 

Recommended references:

http://hos.ufl.edu/protectedag/Strawberry.htm

Scientific information is available upon request.

This article was contributed by Ben Safronovitz. He is a regular contributor to the Under Cover Magazine and can be contacted via This e-mail address is being protected from spambots. You need JavaScript enabled to view it

Last Updated on Wednesday, 31 August 2011 17:47