Hydroponics FAQ

The pH should be kept between 6.0 and 6.5 with 6.3 the ideal range.

Lighting hours depend on the plant’s growth phase.

Seed raising = 24 hours per day
Cutting phase = 18 hours per day
Vegetative phase = 18 hours per day
Flowering phase = 12 hours per day

This can be caused by too much fertilizer, too much salt in the water, not enough water, lights placed too close to the plants or poor air movement in the grow room. Certain nutrient deficiencies can also cause tip burn. Use a well-known brand of nutrients, and if in doubt, change the solution.

It is best to maintain nutrient solution temperatures between 18°C and 22°C. Temperatures below 18°C will cause growth to slow. It is necessary to add heat to your grow room in cooler seasons.

There can be a number of reasons for this. First, you must eliminate the obvious elements that could be causing death, like lack of water or high temperatures. Root diseases like pythium are quite common and can cause sudden death of plants as well as low yields and a complete collapse. Microbial cleansers have been proven very useful in the treatment of root zone problems. As a preventative measure, the risks can be reduced by way of friendly bacteria, which break down the dead root matter and convert it into useable compounds that the plant can absorb.

Plants stretch when the light is insufficient or humidity is too high. Lack of ventilation is normally the cause of high humidity. You should always have the air coming in the same as the air going out at the same rate. You need at least 20 to 30 air changes per hour.

Humidity is best maintained at 50 per cent in the centre of the plant canopy, although between 40 per cent and 60 per cent is acceptable. Too high a humidity runs the risk of disease and stretching.

Room temperatures need to be maintained at around 28°C in the vegetative phase and a couple of degrees lower in flower. It is better also to have dark period temperature lower than the light period temperature. 15 – 18°C is ok for flower. Always run your lights during normal daylight hours and allow normal light temperatures to produce the cooler period. This is an essential process for correct flower maturation.

Ventilation needs to be enough to maintain a temperature of about 28°C and a humidity of about 50% in the centre of the plant canopy. Generally it is better to have too much ventilation than too little. As a rule of thumb, during summer give about 120 litres per second of air going in and the same amount being vented per square meter of floor area. Try to maintain the temperature inside no higher than outside. In winter, vent according to temperature and humidity, you will usually need less ventilation.

The success of any system will depend on the management. The best results are often achieved with the simplest of systems. When choosing a nutrient / reservoir tank use a minimum of 45 litres per square meter of growing area. Less than this requires frequent adjustments.

As with systems, there is no “best” medium. Each medium requires different management, but expanded clay tends to be easy to manage and very effective, with good moisture retention and good drainage.

There is no hard and fast rule on this one. Generally the inferior quality brand nutrients require dumping more often than the superior ones. The size of the reservoir relative to the number of plants is also important. Using quality nutrients would only require dumping every two weeks, although most experienced growers dump every week to keep water quality at a premium. To save water and money, invest in a nutrient meter. This way you can check the strength of your nutrient solution and "top up" rather than replace.

The optimum amount of light to use is usually between 400 and 600 watts per three square meters of growing area. Generally allow 100 watts of light per plant.

For ease of control, use a minimum of 45 litres per three square meters of growing area, as less than this requires frequent adjustments. A rule of thumb is at least 50 per cent should remain in the tank during irrigation.

There are a number of good nutrients on the market. Unfortunately there are also many nutrients that are cheaply made and don’t do the job properly. Any well-established brand that uses technical grade mineral salts should be suitable. Ag-Grow is our own brand of nutrient and is an easy recommendation.

The best water will have low salts and no contaminants. Household tap water should be okay; if you can drink it yourself, it is should be satisfactory for your plants. The best way to test is to sample some, and if you get a significant CF reading it may be wise to invest in a counter top water purifier.

Aerating the nutrient solution is a good idea. It guards against stagnant water, helps mix the nutrient and stimulates root development.

These are troublesome pests known as red spider or “spidermite.” They can cause severe damage by destroying the plants chlorophyll, and the plants should be treated as soon as possible.

The time taken to strike roots on clones varies according to the time of the year and the health of the clones. About five to 12 days is normal. Using rootzone accelerant in the tank and stress guard as a foliar spray will increase the strike rate significantly as well as the subsequent health of the plant.

Brown roots (root rot) are usually those that have been attacked by disease, probably “pythium.” Using a microbial cleanser will be of great assistance and usually eliminates the problem. Normally, healthy roots should be white with fine hairy air roots. Another frequent cause is too high a flow of water which can't drain quickly through pot drainage holes blocked by roots growing through. Dead roots, whatever the cause, will always go brown.

The purple colour is a pigment called anthocyanin. It is produced by plants that are growing under some stress. It is often caused by cold growing conditions. It also often happens during flowering and is a deficiency of either potassium or phosphorous, so you will need to increase your nutrient levels.

Whitefly, thrips and caterpillars can also be troublesome. Proprietary remedies are available for specific pests.

This is probably a disease called botrytis (grey mould), best controlled by maintaining optimal humidity. Regular use of a friendly bacteria/fungicide will help control botrytis as well as many other fungal problems.

The flies are probably scarid flies (fungus gnats). Their larvae can cause severe damage to feeder (hairs) on roots. Treat them with a suitable bacterial inoculant or soil drench.

This can be caused by a number of factors. Any of these reasons can stop the plant from taking up the nutrient in the correct quantities and balance.

• Low oxygen levels due to lack of aeration or too much water;
• The onset of root disease;
• pH is too high;
• The solution is too hot;
• Too much salt in the water.