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Greenhouse Production Auburn's Plant Science Research Center's Certified as Organic Production Facility |
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Potting Mix and Fertilizer Trials
Last winter we evaluated some commercial organic potting mixes and liquid fertilizers on the growth of plants in the greenhouse. Three commercial potting mixes and one home-made potting mix were evaluated:
Fertilizers Used: Three commercial soluble fertilizers approved for organic production were evaluated in combination with the potting mixes:
Two trials were conducted with different size pots. In the first trial, Zinnias were grown in plug trays. The VT Compost product, Fort Lite, was clearly the best potting mix evaluated for plug tray production. It was the only one that contained enough nutrients to take the plants to transplanting time. The results indicate that in plug tray production, a potting mix that contains a nutrient source, such as compost, performs better than one that relies on the application of soluble fertilizers for needed nutrients. Pinnacle was the most effective fertilizer evaluated. Omega 6-6-6 also performed significantly better than the control, but Neptune’s Harvest fish/seaweed blend did not. The performance of the fertilizers was directly correlated to the label rates. The fertilizer that was used in the greatest amount was the one that performed the best. The label rates for the fertilizers were as follows: Pinnacle 21 T/gallon Omega 6-6-6 2 T/gallon Fish Emulsion 1 T/gallon
The plan had been to transplant the seedlings to larger pots at 6 weeks, but at 35 days they were so root bound and in such poor condition that it was doubtful that they could recover sufficiently to yield useful results. Consequently, the experiment was terminated at 35 days. It was decided to conduct a second trial with zinnias in larger pots (4.5”) using the best potting mixes of Trial 1: Fort Lite and worm castings mix with the same fertilizers, but at different application rates. Three different rates were evaluated for each fertilizer: 1= low rate = 5T/gallon 2 = medium rate = 10 T/gallon 3 = high rate = 20 T/gallon (Pinnacle label rate) Additionally, pure worm castings were evaluated as a potting mix.
The results of the second potting mix experiment were inconsistent with those of the first experiment. Whereas the Fort Lite mix performed best in the plug trays, the worm castings mix initially performed best in the 4.5” pots by getting the plants off to a fast start, but by 20 days there was no difference between the potting mixes.
The results of the second experiment indicate that Fort Lite and pure worm castings contain enough nutrients to carry the plants in the larger pots until flowering time and good flowering was noted on all plants around 45 days after planting. There was no benefit to applying fertilizer to plants in these two potting mixes in the first 6 weeks of growth. The plants growing in the worm castings mix, however, did increase in growth with the addition of fish emulsion, which indicates that this potting mix did not have enough nutrients to carry the plants to flowering time. The worm castings mix was 20% worm castings.
The greatest fertilizer effect was observed with Neptune’s Harvest Fish and Seaweed fertilizer applied at the medium rate, 10 tablespoons/gallon, which is 10 times the label rate. The label rate for this product is very low; only one tablespoon/gallon. The company says this is to prevent odor when used for houseplants, but applying fish emulsion at higher than label rates did not damage the plants and it produced better results with the one potting mix that benefited from additional fertilizer. Omega 6-6-6 fertilizer burned the plants even at the lowest rate applied, which was 2.5 times the label rate. Pinnacle also burned plants at all rates applied, though all applied rates were below the label rates. This could be due to a salt effect of the larger amounts of fertilizer used in the larger pots as compared to the plug trays.
Beneficial Insects Jane Hoehaver, director of the Plant Science Research Center, likes to feed her beneficial insects well—with aphids.
Jane explains, “We are trying to establish banker plants, which are winter and summer barley. Basically, they hold cereal aphids, which in turn serve as a food source for beneficial insects that we release. The cereal aphids only feed on monocots, or grasses, so they won’t bother our tomato and pepper.” When she releases beneficial insects, she will do so directly on the banker plants to give the insects an immediate food source: the aphids. Later, when the tomato- and pepper-eating aphids come, the beneficials will be hungry and plentiful enough to protect the plants. Jane releases two beneficials: parasitic wasps and gall midges.
The winter and summer barley are available at Seeds of Change and Johnny’s Seeds. Both are organic seeds. Update
"We will have to repeat the test after the organic transplants are delivered to the field. Before we were able to innoculate the banker plants with the cereal aphids and get beneficials established in the zone, we were inundated with green peach aphids. Along with the infestation of aphids, we also discovered parasitic wasps that found their way into the greenhouse. "Although we purchased beneficials to combat the problem, the insectory that we use had problems with their insect colonies and delayed our original shipments until April 17. In the mean time, we used neem oil sprays to control the aphids. Control is the key word as neem does not eliminate them 100%; it only decreases the numbers. This spray kills the parasitic wasps as well. "The good news is that the developing parasitic wasps housed in the aphid mummies on the plants are protected from the sprays by the deteriorating body of the aphid. So, if the amount of mummies is relatively high we can spray and still have a future generation of wasps available. This does leave a lag between the beneficials and the pests as the pest populations build more quickly than the beneficial population. At this point, to try and evaluate the banker plant system would be pointless. When our production is over, I'd like to empty and clean the zone, start fresh banker plants, inoculate with aphids then beneficial, and re-evaluate the system."
To read more about these beneficials visit http://www.biobest.org/
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