HYDROPONIC STRAWBERRY CULTIVATION

THE PRODUCTION OF FRESH STRAWBERRIES provides an excellent opportunity for home and market gardeners to enjoy a better-quality fruit and perhaps generate a little side income. Large-scale outdoor hydroponic cultivation could replace traditional strawberry growing methods in some of North America’s largest producing areas. This is largely due to environmental and health concerns raised and lobbied concerning commercial fumigants, on which conventional field-berry growers rely heavily for disease, weed, and nematode control.

In other areas of the world, and in some progressive North American operations, large-scale hydroponic strawberry production has been practiced in earnest for some time now. Because the plants are no longer grown in soil, commercial soil fumigants are no longer required, significantly reducing any potential harm to the consumer or the environment.

So, what is the significance to the home or market gardener? Strawberries do not store or transport well. Some commercial varieties are bred for better post-harvest handling characteristics, but this can compromise taste — namely sweetness in the strawberries. This provides an excellent opportunity for small-scale commercial strawberry production to support local demands. It is advisable to target production and harvesting periods when local prices are at their peak, typically during the winter and early spring months. In most regions a greenhouse or cultivation indoors under lights is necessary during these peak periods due to outdoor climatic limitations. Currently, the media are discussing the “100-mile diet” wherein the consumer makes a conscientious effort to purchase food that is produced within a hundred-mile radius.

As with any growing endeavor, variety and selection is the key. Strawberry varieties best suited for greenhouse cultivation are classified as being short day or day neutral. Basically, these plants will flower and produce fruit with shorter photoperiods. Sweet Charlie and Camarosa are popular short-day varieties while Selva and Seascape are commercial day-neutral producers. These are proven varieties. Temperatures also play a role in triggering a strong flowering and fruiting response in strawberry varieties. Indoor growers gardening under lights have the luxury of choosing whatever variety best suits their operational budgets or personal tastes because photoperiods can be maintained as long or as short as required to produce fruit. For example, growers using HID lighting can produce long-day varieties, which would be impossible for commercial field growers during seasons with shorter light durations.

Market gardeners also have the important option of producing their crops organically, which is often more feasible for the smaller-scale commercial producer. If properly marketed, organically grown berries can fetch a considerable premium over conventionally produced varieties, and can enjoy a stronger demand amongst select clientele.

In either case there are a variety of methods by which the home or market gardener can produce their crops. Hydroponic systems such as NFT or perlite-filled bags are favoured among berry growers. Strawberry roots don’t do well with water pooled around them. In an active recirculating system such as NFT, good aeration of the nutrient solution and ensuring that the channels drain well is important. Maintaining reservoir temperatures below 70°F (~21ºC) will also promote a healthier root system less susceptible to infections of Pythium, which can spread quickly in a system where warm, stagnant conditions prevail.

It is advisable to inoculate the root systems of young plants with beneficial bacteria and fungi, such as species of Trichoderma and Bacillus. An additional source of carbohydrates will help young plants thrive as well as nourish and assist the beneficial microorganisms that have been introduced. From time to time, growers might choose to reintroduce the microorganisms to the growing system to help ensure that higher populations of aerobic organisms outnumber anaerobic (bad) microorganisms.

Occasional applications of products with enzymes that are intended to promote healthy root systems are also recommended. These enzymes will help hasten the biological breakdown of old or decaying roots. Not only does this help to further eliminate the possibility of contracting a root disease, but the end products of the breakdown of old or decaying root matter supply many substances that are beneficial and that can be taken up by the crop. The enzymes also perform a sort of “bio-chemical peel” to the roots; they will strip away residue that has accumulated on the roots and can impede nutrient uptake to a degree.

Organic growers will also reap additional benefits from applications of enzyme-based products intended for the root system. These enzymes will noticeably increase the availability of organic nutrient components because they help to solubilize organic materials into forms that are more available or “digestible” to the plant. Recently, in working with a grower using these products, it was determined that the enzymes were actually raising the parts per million (ppm) of the growing solution by about 250 ppm over the course of a few days. This was noted in a drain-to-waste system, where the nutrients were mixed and then applied over the course of a few days between mixing of new batches.

Perlite appears to be the medium of choice for greenhouse and indoor strawberry producers. Compared to a system without a medium, such as NFT, they are much less temperamental and less prone to disaster in the event of a power failure or other stresses to the crop. Using a more medium-based system allows the grower to use a wider range of products throughout the cropping cycle. In European nations and Israel, where protected strawberry production has been practiced for considerably longer than in North America, growers tend to prefer medium-based production with perlite over other hydroponic systems. Perlite tends to be ideal because it is fast draining, lightweight, near neutral in pH, and relatively inexpensive, and it has little or no cation exchange capacity (CEC).

Because of perlite’s relative light weight as a growing medium, it is ideal for use in hanging bag systems. Because strawberries exhibit a low growing and trailing growth pattern they are especially well suited to vertical gardens. Vertical gardens maximize the efficiency of the overall volume available for plant production in a given area. Using vertical growth systems allows producers to gain more than 100 per cent in efficiency of their floor use.

A-frame–type structures such as aeroponics or specialized benching are another option in making use of vertical space, although hanging bags are most common. Some newer designs intended for strawberry production suspend rows of troughs upon which sacks filled with perlite planted with strawberries are suspended a couple of metres from the ground. In this configuration aisles are eliminated. Because the plant growth tends to hang down from the suspended height, greenhouse operators are able to eliminate aisles typically required for walkways to access and harvest the crop. In this fashion, maintenance and harvesting of fruit can be done from below the growing system; the operator just needs to walk beneath and reach up. This also helps to improve air circulation in the growing environment and helps to ensure fast drainage in the root zone.

Average yields per cropping cycle on many commercial strawberry varieties are about two pounds of fruit per plant. Keep in mind that these are commercial figures using more conventional nutrients and very little in the way of nutrient supplements. Innovative gardeners with less space to manage can choose to boost their crop’s performance with additions of organic teas, enzymes, beneficial micro-organisms, carbohydrates, and specialty flowering and fruiting supplements. Supplementing the growing environment with increased levels of carbon dioxide will also significantly increase production and reduce cropping times. As a hypothesis, an experienced home or market gardener could bolster conventional yields by anywhere from 50 to 100 per cent with a well-designed nutrient and supplement program, compared to ‘bare bones” nutrient regimens.

For perlite culture, the following is suggested for optimal base nutrient levels in the final solution (conventional nutrient programs): N: 80 ppm, P: 50 ppm, K; 85 ppm, Ca: 95-100 ppm, Mg: 50 ppm, S: 56 ppm, Fe: 2.8 ppm, B: 0.6 ppm, Mn: 0.4 ppm, Cu: 0.1 ppm, Zn: 0.2 ppm, Mo; 0.03 ppm; pH: 6.0-6.2; EC: 1.4-1.6 mS/cm.

Strawberries are typically self-pollinated plants, similar to tomatoes. For indoor and greenhouse environments the grower will benefit the crop greatly by helping to disperse the pollen. Indoor growers using artificial lighting might use mechanical vibrators to help disperse pollen, whereas greenhouse growers might introduce specific varieties of bumblebees — typically 50 bumblebees for 500 m2 (600 sq. yd.) of greenhouse space. For good production levels to be achieved, pollination is critical.

For control of fungus gnats in the root systems, Bacillus thurengiensis is added through the fertigation system in two-week intervals.

Mites, aphids, and thrips are common pests that might infest strawberry crops. Biological control methods are safe, economical, and effective with proper applications and timing. Geocoris punctipes, Orius insidiosus, and Neoseiulus californicus are predator varieties that have been used commercially in strawberry crops with a level of success.

Powdery mildew can also be problematic in greenhouse and indoor strawberry production. Commercial producers in Florida have been using a bio-fungicide containing Ampleomyces quisqualis as a measure of control in all stages of plant and fruit development.

For any would-be producer, researching cropping methods, varieties, and markets is essential. This article is not intended to be a definitive guide for producers, partly due to the volumes of information available, but a brief overview intended to offer some insights into some aspects of this as a potential outlet for home and market gardeners looking to supply themselves with top quality produce and perhaps a little extra income.