Hydroponics for Health: Growing Watercress and Wheat Grass

While many of the fruits, vegetables and herbs we grow in hydroponic system are tasty and nutritious, some plants are grown more for their health giving properties. Water cress (Nasturtium officinale) and wheat or barley grass are two such plants which have recently been growing in popularity for the health benefits they can offer us. Watercress, a member of the brassica family, not only has good amounts of vitamin A and C, calcium and iron, but also folic acid. It has also been studied as a source of certain cancer fighting compounds - isothiocyanates, which are protective against carcinogenesis, making its popularity as a health food as well as a salad green grow rapidly. Wheat or barley grass juice is also a ‘health promoting’ food which consists of freshly cut young sprouts which are juiced and taken immediately without cooking or heating. In this form, the juiced grass extract contains a high level of chlorophyll, as well as beta carotene, B group vitamins, Vitamin C, minerals, amino acids and and enzymes which many claim have great health benefits.

Both watercress and wheat grass thrive in small, simple hydroponic systems - producing sufficient fresh forage for a household. For indoor growers, soilless or media less systems can be used for both plants, keeping the growing operation clean and the final product clean and grit free.

Watercress:

Watercress is actually an ancient green vegetable that has been grown for many centuries, both for its health giving effects and its distinctive peppery flavour. Being a semi aquatic plant, it’s well suited to solution culture where it can be cut many times and will rapidly re-grow within a few days for future harvesting. Good varieties of water cress exist nowadays - the main one being the ‘aqua large leaf’ type which is grown commercially as a cut salad green or vegetable. Plants can be raised from seed initially, however once a few mature plants have been grown, stems can be taken and used as cutting material for more plants. Watercress forms many new roots at each stem node and is easy to grow from stems purchased at the grocery store if seed raising is too slow for smaller growers.

Growing watercress

Water cress is fairly tolerant of a wide range of temperature conditions, however it has two requirements for optimum growth - high quality water at a cool temperature of 12 - 18°C combined with air temperatures in the range 20 - 26°C day and 15 - 20°C at night. Yields with hydroponic water cress crops grown under these conditions range from 1 - 1.6 Kg per square meter per month. However in the cooler conditions of winter when light levels are also low, production can drop to below 500g per square meter per month, unless some form of environmental control and heating is used. For this reason hydroponic water cress is often commercially produced year round under crop protection structures or in greenhouses, however it also thrives in indoor systems where it has a similar light requirement to lettuces and other leafy herbs.

Temperatures below freezing and frosts will result in plant die back, although crops will regenerate from underground root systems when conditions warm up again. The minimum temperatures sustainable in a commercial operation are 10°C.

Watercress is fairly easy to cultivate. It prefers to grow in cool (12 - 18°C) flowing water at various depths with partial shade in summer. Seeds can be purchased from garden centres and commercial vegetable seed suppliers in bulk quantities. Seeds should be sown into cell trays of media or cubes of inert media such as rockwool which retain high moisture levels. Germination will occur in about 7 - 10 days. Seed should only be sprinkled on the surface of the media and lightly covered with clear plastic to retain moisture. Stems will also form roots at each of the nodes, so stem and root cuttings can be taken at any time of the year. For commercial cultivation, flowers should not be permitted to form as this results in bitter flavours developing in the plant foliage. Regular cutting for harvest will ensure plants do not flower, but any flower stalks should be removed from mature plants to encourage further leaf development.

Hydroponic systems used for commercial water cress production are either based on large outdoor gravel beds or NFT (Nutrient film technique) channels made from PVC gullies or plastic film. Outdoor gravel beds should be 15 - 20 cm deep, lined with plastic and filled with at least 100mm of free draining media such as clean gravel or river sand. Nutrient solution is flooded into these beds several times a day with drainage occurring due to a fall of at least 1:100 down the bed. Nutrient is then pumped back to a holding tank ready for the next flood cycle. For smaller growers, NFT, or DFT, aeroponics or float systems suit watercress, as do most ebb and flow systems provided sufficient flood cycles are maintained to keep the plants moister than most other crops.

Harvesting of water cress is carried out once per week under good growing conditions. At harvest, the plant should be cut back to half its size. This allows some leaf area to remain to support regeneration of the plant for the next harvest. Water cress plants will eventually need to be replaced after several cuts or harvests to maintain good yields.

Watercress Pests and Diseases

Watercress is prone to the usual insect pests which affect vegetable crops. Aphids are common, particularly in spring, as are caterpillars at certain times of the year. Aphids can often be controlled with the use of oil or soap sprays before heavy infestation occurs. Caterpillars and other insect pests can also be controlled with safe botanical Neem insecticides or for heavy infestations, commercial pesticides can also be used provided the correct with holding period before harvest is applied. In cases of uncontrollable pest/disease outbreaks where pesticide products can not be used (such as in organic production), the crop can be cut back and left to regrow healthy new foliage.

Diseases of watercress include mildews, rust, leaf spot and Botrytis (grey mould). Many of these diseases can be prevented by ensuring there is adequate air flow through the crop, reducing humidity build up which makes the plants prone to disease. Fungal diseases can be prevented by applying a dilute spray of sodium bicarbonate to the plants at regular intervals. Bacterial diseases such as bacterial spot or leaf spot can be controlled with use of copper based plant protection products. Seedling diseases such as Pythium (‘Damping off’) can be prevented by using the beneficial fungus ‘Trichoderma’ based products which can be drenched into the seedling media or applied via the nutrient solution.

Harvesting

Plants can be harvested anywhere from 4 - 10 weeks after transplanting, depending on growing season. Plants raised in spring and summer should have sufficient foliage development for a small first harvest at four weeks. Winter grown crops can take 10 weeks before harvesting should begin. Water cress should be harvested with a sharp knife to slice cleanly through the stems. A sharp knife will lessen tissue damage to the plants and the harvested stems and prolong storage life. Harvesting should be carried out early in the morning when temperatures are cooler and the plants turgid. Stem lengths of 15 cm are preferred. Bunches should be cut, bundled, dead leaves and damaged stems removed, and placed into plastic bags as quickly as possible. Hydroponic water cress should not need washing if it has been grown under protected cultivation. Water cress should be stored wrapped in plastic under refrigeration at 2 - 4°C. Misting of the foliage will assist to retain storage life for many days.

Wheat and barley grass:

Sprouting and growing wheat or barely grass is one of the simplest hydroponic systems to set up. No media or soil is required for this process, making a quick and very clean system to produce harvests of fresh juice each day. The grains to be used should be purchased as specifically for sprouting - that way you can be assured that no chaff or seed treatment chemicals have been used on the grain. The grains should then be soaked overnight in water, drained, rinsed and then evenly spread onto a solid plastic tray lined with two layers of paper kitchen towel. The paper towel holds sufficient moisture for the grains and no other media is required. Wheat or barley germinates best at temperatures around 20 - 22°C, although there is a wide range at which the grains will germinate, lower temperatures mean slower overall germination and growth. The trays can then be covered with plastic for the next two days to retain moisture. Once germination is seen, the plastic can be removed and the germinating seeds lightly misted with water only when required. Getting watering right is important - too much water and root rots will occur just as they do with any other type of soilless system, not enough water and the growth rate will be affected. The base of the grains should be damp, but not ever sitting in water as they begin to rot and fungal/bacterial growth can occur.

After approximately five days growth (or when the young seedlings are about one to two inches tall, some nutrients can be used. Initially the grain contains sufficient energy for seedling growth and no nutrients are required. However about day five or six, these stored reserves in the grain are exhausted and nutrients are required for the young plant. Either pouring nutrient solution into the base of the growing tray or misting over top with low strength, general purpose vegetative hydroponic formula is sufficient at this stage. An EC of around 0.4 - 0.8 (use lower EC if conditions are warm and high rates of evaporating are occurring, use the higher EC under lower light and temperature conditions), will be sufficient for growth of the grains over the next week or two. Since nutrition of the young plants at this stage will determine the quality of the final juiced product, selecting a high quality, complete hydroponic nutrient product is important. If possible use a nutrient product that has some of the ‘beneficial elements’ such as selenium, silica, chromium, iodine etc. added in as this will help boost mineral levels in the grass, many of which are important for human health.

If conditions are really warm and growth rates rapid, applying nutrients at one watering and only water at the next will be required to make sure salt build up does not stress the young plants. After a weeks further growth, the grass can be cut and juiced at what ever stage you prefer. Generally wheat or barley grass is cut while still quite young, to get the best health benefits, but the plants can actually be grown on for several weeks provided sufficient nutrient is applied. After harvest, the root mat can be rolled up and composted or disposed of, the trays cleaned and sterilised (10% bleach solution, or hot water and detergent), ready for the next crop. For those who like to juice the whole plant - roots, stems, leaves and all, the grains can be sprouted on solid trays with no paper towel, provided sufficient care with watering and nutrition application is carried out. By having a number of trays at different stages of development, fresh wheat grass juice can be made each day and consumed fresh - avoiding many of the problems of storage and enzyme loss that can occur when the juice product is stored before use.

Summary

Now combine a glass of your own fresh, wheat grass juice with a watercress sandwich and get a double dose of the best health benefits hydroponics can offer!