Grow Medium Problems

by Jordan
(Seatte, Wa, USA)

I am a beginner with hydroponics, and unfortunately I found your site after I set up my garden. I have a 4' x 2' ebb and flow system with a 8 bulb T-5 light system. I am using Roots Organics Coco mix soilless medium mixed with hydroton pellets. I am having drainage issues which is why I added the pellets.

I am growing herbs, lettuce, spinach, peppers, tomatoes and cucumbers. I realize this is a broad mix, and next time I will do things differently. I am also using Roots Organics nutrient solutions. All of my plants are small, with different discoloration problems. I am not sure if I am over watering, if my nutrient solution is lacking something, or if my problems have to do more with the light (which I understand should have been an HPS or Metal Halide?) I guess I am having problems across the board, and would love some advice on where to start to improve my system. Thanks.

Answer: Jordan- your post had brought back memories....one of my very first attempts at hydroponic gardening I made EXACTLY the same mistake, and I also added clay pellets to my coco coir to try to correct the problem. For the most part, you should try to use fast draining mediums whenever you are hydroponic gardening. The main exception would be drip systems, which irrigate very slowly and do not work quite as well in mediums that do not absorb water quickly (such as clay pellets).

Coconut coir is a medium, like peat, that sucks up water quickly and holds onto a LOT of it. Clay pellets, on the other hand, do not suck up water quickly and they drain quickly. When using straight clay pellets for the medium, it would be appropriate to flood them for about 20 minutes to let them soak up a lot of water....and to repeat the process three or four times a day. When using a medium like coconut coir, however, you might be able to get away with flooding the medium for a minute or two just once a day.

Currently, your containers are almost certainly over watered. Adding an air pump and air stone to your nutrient reservoir will help a little to provide oxygen at the root level- at least the roots will get some oxygen each time the plants are irrigated. With the mix you currently have in there, I would recommend shutting off your hydroponic system after the next flood cycle and see how long it takes before the first plants begin to wilt. This will give you a much better idea of how often they would benefit from a flood cycle.

If you continue to have too many problems with the coir, you might want to consider a faster draining grow medium for your next try. Straight clay pellets work good in a DWC or flood and drain system, plus they are re-usable.... eliminating the extra expense of always having to replace rockwool or coconut coir.

Your mixing of all those plants is not a bad as you might imagine. Herbs, spinach, and lettuce have very similar nutritional requirements and can be grown together (using a 50% strength vegetative stage fertilizer). All three produce edible parts during the vegetative stage, and so there is never any reason to give them any bloom fertilizer or to give them a 12-12 light cycle.

Likewise, the tomatoes, peppers, and cucumbers require very similar nutrients and nutrient strengths and should do just fine when grown together (although vine plants sometimes become a little unmanageable in a hydroponic system). They can all be started in the veg stage on 50% strength veg fertilizer and can be increased slowly week by week- always watch the leaves of your plants closely when doing this. When one of the plants begins to show the very first little signs of leaf tip burn, you have identified the highest strength of nutrient solution you will want to feed those plants. In fact, you can probably back off the nutrient strength just a little bit at that point. Further more, they might not get to that point until they are in the flowering stage and receiving the bloom fertilizer. All three should do just fine at 900 ppm of the bloom formula, although they might even take more than that before they show any leaf tip burn.

Also, many tomatoes and some peppers require a 12 hour dark period in order to produce fruit properly....a crash course on this can be had on my flower forcing page. This is actually a good reason to keep the two different crop types in two totally different rooms (sorry).

All of this is assuming that there are NO nutrients in the grow medium. Otherwise, the feeding needs to be adjusted to take into account the nutrients already available in the planting mix. Unfortunately, the Roots Organics Coconut Coir you used contains not only coconut fiber, but also pumice, worm castings, bat guano, kelp meal, oyster shell flower, greensand, soluble kelp, glacial rock dust, and leonardite.

I think the coconut coir would be much better suited for organic gardening than hydroponic gardening. Hydroponic gardening is much easier when the plants are getting ALL of their nutrients from the water they are given, which takes extra variables (like how much nutrients are in the grow medium) out of the equation. The grow medium should only be there for physical support and for its ability to retain the nutrient solution.

On a bright note, I believe the nutrients you are using are complete, and don't believe them to be lacking anything.

It may surprise you to learn that your lights are the least of your worries. T5 lights are not your average fluorescent lights, and are perfectly capable of growing tomatoes and other plants that require lots of light. On average, T5 lights will produce about half as much as a sufficiently sized HPS light (and also less heat).

While not as strong as a high pressure sodium light, they are sufficient as long as you keep the plants within about 30 inches from the light. On that note, you may find it necessary to train the taller plants sideways a little bit, or else flower the top 2 1/2 feet of each plant and prune everything below that down to the main stem. This will force any nutrient to move up the stem to a spot where the plants are actually getting enough light to use the nutrients.

Unfortunately, it would be impossible for me to diagnose all of the discolorations in all of your plants, but I am certain it is a combination of too much water in the grow medium and (possibly) too much fertilizer. When plants receive less light, they should also be given less food. Since T5 lights are not as bright as a HPS light (for example), and since the coconut coir you used already had some organic nutrients in it (how much exactly is hard to say), there is a good chance they have been a littler over-fertilized (though I would expect a little leaf burn if that is the case).

Well, I suppose you have a lot to digest. I sure hope this helps you out some Jordan. Feel free to drop me a line if you have any more questions, especially when you begin getting ready for your next go at it. And Happy Growing!