Ask Erik

In Australian winter, you stand a much better chance of harvesting some nice fruits, provided the roots of the crop don’t get too cold. It’s usually much easier and less expensive to heat nutrient solutions versus cooling them. When temperatures in the reservoir get over 90°F, cropping trouble usually isn’t too far behind.

Although tomatoes can be grown successfully in NFT (Nutrient Film Technique), the shallow troughs are better suited for crops with smaller root systems and fast cropping times, like lettuce for example. If you are a die-hard fan of NFT, you might continue using the system with a few modifications, including the bio-filter, provided the system and bio-filter are inoculated with beneficial microbes such as trichoderma and bacillus species. The goal here is to colonize the system with beneficial microbes, leaving no room for pythium to thrive.

During the summer months, a reservoir chiller or titanium/stainless steel cooling coils in the nutrient solution are recommended to help moderate reservoir temperatures. However, because there is not a lot of solution typically around the roots in NFT, the high temperatures will still have negative effects because the thin film of chilled solution will not be able to buffer temperatures sufficiently.

Insulating the troughs and chilling the solution would help keep root temperatures more reasonable. I don’t recommend cycling the nutrient. The nutrient solution in most NFT systems is relatively static. It should be kept moving constantly to keep it aerated and to keep the roots protected, as the film of solution is the only thing standing between naked plant roots and environmental extremes. In very large commercial NFT systems, when the pump stops, the reservoir can overfill because so much solution is being circulated and contained in so many lengths of NFT troughs relative to the holding capacity of the reservoir.

If you are willing to try something new, I would recommend growing in a “DFT” system. This Deep Flow Technique works similarly to NFT, except there is a much larger chamber for roots and the depth of the solution is much greater, effectively buffering bare rooted hydroponic plants for extremes in nutrients or the environment. Essentially, for each large plant, there is about two gallons of nutrient solution. A popular brand of hydroponics system uses this principle with NFT type tubes; however, there is an adjustable overflow in each of the tubes, allowing for larger amounts of nutrient solution to surround the plant roots. For your applications, something along these lines may work out better than the thin film of nutrients that NFT systems provide. DFT systems use much higher flow and circulation rates than NFT systems, helping to saturate DO (dissolved oxygen) levels in the nutrient solution, reducing the incidence of pythium. You can construct your own DFT system out of any large sized troughs that are opaque and chemically inert, so long as you can include an adjustable overflow (to control the depth of the solution) and have a nutrient injection manifold running the length of the troughs to keep the roots and solution will aerated. If you build your own, you can insulate the troughs to keep the roots warmer in the winter and cooler in the summer.

Another suggestion is to only select tomato cultivars that are documented to have a natural resistance to root pathogens such as pythium. Note that some varieties of tomato seeds will be much better suited to hydroponic cultivation versus others. Check with reputable commercial seed suppliers. Inoculating young plants with beneficial microbial solutions will also help to prevent the incidence of root diseases, and should be re-applied several times throughout the life of the crop to ensure optimal populations of beneficial root life and maintain a healthy life balance in your bio-filter.

I hope this helps you out, and send us some pictures of your winter tomatoes.

Cheers, Erik Biksa