Since my last greenhouse post, I have made some changes to my hydroponic system. It didn't take long to realize that algae can be a big problem in a hydro system. I liked the flexibility of using open gutters in my NFT system for being able to move plants around and to adjust their spacing. However the strong spring sun and warmer temps quickly left everything in contact with water covered in thick algae. This led to other issues such as unhealthy roots and root rot. Healthy roots in a hydro system should be bright white not brown and certainly not green.
I realized that I needed to cover the gutters as best as possible so I cut some strips of leftover greenhouse siding to fit into the gutter, cut holes in the strips and reinserted the net pots. I used my skill saw so the strips are a little rough and don't fit as well as they could. Adding some spacers under them to keep them out of the nutrient solution solved this easily enough. This seems to be working pretty well but I think I will eventually want to replace the wood strips with plastic to prevent mold and rot and for easier cleaning.
|Cucumber Inserted into Cover Strip|
Another part of cleaning up the gutters was to remove my spinach as the roots were covered in algae and the plants were beginning to bolt. Most of the spinach was replaced with some head lettuce, more chard, some peppers, cucumbers, tomatoes, basil and collards (peppers and tomatoes will probably go into another hydro system when I get time). I did not replace the collards and rainbow chard as they seem to be doing well. In fact, the collards do amazingly well in this type of system and three plants have produced more smoothie greens, salads and wraps than my spinach and chard combined.
|Collards and Chard|
I would also have to say that the lettuce is doing extremely well also. I have one plant that is nearly 15 inches across after only about 30 days.
Or should I say, was doing extremely well? As time went on, I noticed my lettuce wilting. At first I thought it was because of the heat but then noticed that it seemed to be wilting earlier in the day while still cool. After some research, I concluded that my problem was probably due to lack of oxygen caused by water damming in the system and that I was drowning the roots. This was also aggravated by some of the larger plants like the collards and chard which had huge root masses causing water to build up behind them. I therefore had to rearrange all of my plants so the larger ones were at the upper end of the gutter leaving the younger plants down stream to have only a thin film of water passing under their roots. I also got a timer to turn my pump on and off throughout the day so the gutter would have time to empty completely allowing the roots needed exposure to oxygen.
I wasn't sure what the best timer settings should be but finally decided to have it on for an hour then off for an hour all day long except that it would run constantly for 5 hours during the hottest hours of the day. This seems to be working fine. I will probably play around with the settings more in the future.
The timer actually solved another problem as well which was to allow the aquarium heater time to heat the water in order to circulate warm water over the roots at night. Without the timer the reservoir temperature was only a few degrees warmer than the air temperature as the water flowing through the gutters would quickly cool off through exposure to the cool gutters. Now it warms up nicely between circulations. I am hoping that this does not shock the roots as they are constantly cooling down an being heated up every cycle. The plants seem happy so I guess I won't worry too much.
After these changes, I noticed that the plants were quickly growing healthy roots, taking in more nutrients, and that most of the lettuce plants seemed to be doing better with less wilt.
|New Root Growth|
In fact it was time to have a head of lettuce for lunch. This is the cool thing about hydroponic lettuce as I brought it in and placed it in a bowl of water, roots and all so it would be super fresh for the salad. It turned out that my wife couldn't make lunch that day so I decided to put the lettuce back in the gutter for another day (Try picking a head of lettuce out of your garden and then putting it back). Then...
Looking into the bowl I noticed several small "wormy" things. This wasn't good. Could it actually be that something was eating the roots of my plants that would be causing them to wilt? Back to the computer for more research. I quickly realized what my problem was, fungus gnats.
|Fungus Gnat Larvae|
If you start plants in your greenhouse or have house plants, you've probably seen these little guys. They are the small 1/8 inch flies that flutter around at the base of your plants.
They don't fly well and prefer to run around when disturbed. They lay their eggs in moist areas and the larvae hatch and eat the decaying matter in the soil and, at times roots and the base of young seedlings. I had noticed such damage to some of my potted tomatoes.
|Fungus Gnat Damage in Tomato Seedling|
Now what? It seemed that my potted starts were mostly unaffected by these little guys except for one stevia start that is probably damaged to the point of no return. I still didn't like the idea of all those hidden larvae eating away under the soil's surface. But my real concern was my prize lettuce that was getting damaged as the larvae didn't have any other food in the hydro system other than the roots of these plants. I proceeded to remove the affected lettuce, harvest many of the large leaves, trim the roots and rinse off the larvae. I then sprayed the roots with neem oil, re potted and put them back in the hydro system.
This was only a short term fix. How to get rid of these guys so I'm not perpetually plagued by their presence was the question. I researched solutions and saw that there were lots of products available to kill them. However, most were not available locally and my nearest hydroponic supply store is over an hour away. After much thought and research I decided to try something called BTI or Bacillus thuringiensis israelensis which is a microbial larvicide which kills the larvae of many variety of Diptera. I have read that this would include fungus gnats. This was available at my local garden supply store in several forms. One is in the form of doughnuts and the other is in small packets like tea bags. The former is used in fish ponds and the latter is for watering troughs for farm animals.
I opted for the tea bag variety which will supposedly treat 500 gallons of water. Seems like a bit of overkill but why not.
I placed the tea bag in a 5 gallon bucket of water to make a concentrated solution which I let steep overnight. The next day, I took out a gallon and added it to another 5 gallon bucket and topped off with water. I then proceeded to water all of my plants in the greenhouse with the "killer" solution. I also topped off my hydro reservoir with it as well.
Only time will tell. The BTI supposedly will kill the larva in 24 hours and will continue to work for up to 30 days. It will however not kill the adults which live for about a week. So hopefully in a week or so I won't see anymore of those guys skittering around my lettuce or my starts. I will then be able to cross off one more chore from my list of many allowing me to sit and enjoy my paradise for just a bit longer next time.