Ask Erik - Letters to Maximum Yield

Dear Erik, this is my first bash at hydroponics.I have three marrow/courgette plants in an NFT system. I am using “Power Gro leaf” The conductivity is 14 as the plants are approximately six weeks old and the flowers are forming. I have just pollinated the first female flower.
The light is the growing light (sorry I have not done this long enough to be technical) and on for 12 hours. pH is approximately six. I change the tank every two weeks and have increased the concentration by one - two every week. Started it at six - eight , six weeks ago.
The problem is the leaves which are turning brown and withering away. There are no visible pests like Red Spider on the leaves. The plants are growing apparenty well and new leaves emerge green and healthy, not too pale and not too dark. The leaves turn this brown colour about two - three weeks after forming. While there is still some chlorphyl in the leaves I leave them on but when they go completely brown I remove them to avoid disease. But when I have done this the plant has lost almost all its leaves except the growing shoots. I never had this when I grew marrows in soil.
I thought it was underfeeding and raised the concentration for about two - three weeks but have not noticed any visible improvement. I really do not know what feed levels I should be using. Please help and/or advise
Thanks Sheila

Thanks for your question Sheila.
I am not familiar with marrow plants, but my first thought is a nutrient deficiency. Is the nutrient formulation you are using a “complete” formulation (I am unfamiliar with the brand you mentioned). Growers have tried to use house-plant foods in their hydroponic systems only to find that the formulation is intended for use in soil where many elements are found naturally, while a hydrosystem tends to be relatively inert. Your nutrient should contain adequate:
Nitrogen, Phosphorous, Potassium, Sulfur, Calcium, Magnesium, Iron, Boron, Manganese, Zinc, Copper, Molybdenum, and may contain Nickel or Cobalt (not a necessity, but beneficial).
If any of these elements (except nickel and cobalt) are absent, this is likely the source of your problem. Some tropical plants also require trace amounts aluminium. To enrich your plants with “sub-micros” consider adding pyrophyllitic clay to your nutrient solution or growing medium. Often houseplant foods lack significant quantities of calcium and magnesium (as these are typically supplied as dolomite lime in potting soil). Make sure that the trace elements are chelated (you should see “EDTA”, “DTPA” or “EDDHA” following them). Chelation is necessary in order to make some nutrients available to the plant.
The pH or a re-circulating nutrient solution should be in the range of 5.5 to 6.5. Acid loving plants may prefer a lower pH. Also note that some plants just don’t like to grow hydroponically.
Salt build-up on the roots could also contribute to the necrosis you describe.
If none of the above sound correct, please feel free to provide some more details and we’ll try a second diagnosis.
Sincerely, Erik Biksa

I am a gardener who would like to employ some hydroponic lighting to starting plants in my basement using SunSystem Lighting. I now use six flourescent bulbs over a table with several trays of soil mixture in the traditional soilless mix to start my seedlings. Would the Sun Lighting System help me in growing stronger plants? I looked at a SS 400 lighting system to replace my flourescent bulbs - is this going to be superior to my current system? Does the SS lights benefit from a propagating mat under the seed trays? What should be the distance between the light and trays?
Since I have the equipment to start seeds the customary way in soilless mix do you see adding hydroponic lighting ideas help me? Also would the hydro nutrient solutions be better than fish emulsion, etc? Any ideas you might have would be appreciated.
Thanks
Hank

Thanks for the question Hank. You would be able to provide the young plants with higher light intensities as they become established if you switched to a 400W H.I.D. lighting system. Depending on your planting schedule, you may want to fuel the new plants with H.I.D. lighting for rapid development. On the other side of the coin, the fluorescent bulbs can provide very even light coverage for smaller plants in smaller spaces. By carpeting an area with fluorescent lighting you can achieve intense lighting conditions, although much less efficiently than their H.I.D. counterparts. Also, when using just a few cool-white bulbs (high Kelvin rating) combined with lower temperatures and a mild fertilizer regimen you are able to achieve a level of developmental control by reducing inter-nodal lengths which might be desirable when dealing with low-height spaces or by holding the plants at a reasonable size until more favourable outdoor conditions develop or until you want to intensify the latter part of floral production. Young plants that develop at cooler temperatures tend to produce “harder” growth, reducing transplant shock when transplanting to the outdoors. In the situation you describe, you could use your existing fluorescent lights for germination and early seedling growth and then switch to an H.I.D. bulb once the plants develop three to four sets of leaves. The fluorescent lights can be suspended just a few inches above the emerging seedlings. Provided that there is little chance of the new plants drying out once established, after switching maintain the H.I.D. bulb at a distance of 9 to 12” above the plant canopy. If using a high quality air-cooled reflector the distance can be closer. Watch for signs of heat stress. Lights with a higher percentage of their output in the blue spectrum can induce tighter inter-nodal spacing in some varieties. Thermostatically controlled propagation mats will increase the germination rate and increase the rate of root development. Temperature is one of nature’s most powerful regulators of bio-chemical activity.
I would be more inclined to use a premium quality hydro fertilizer as you have a higher level of control with plant nutrition and all macro, micro, and perhaps sub-micro nutrients will be available.
Sincerely, Erik Biksa