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green_guys

New Micro Urban Farm using NFT

Green_Guys
9 years ago

Hi there,

A couple of friends and I have set up a micro urban farm in Vancouver, BC based on a community supported agriculture model. Our name is Green Guys on The Drive.

We have three vertical hydroponic gardens based on the principles of NFT. There is room for 320 plants. The pipes are 4 inch pvc pipe with a 1/4 horsepower pump connected to two 170 litre rain barrels as the reservoir. Each plant sits in a rockwool cube that is inside a 3" netpot with hydroton.

Last year we ran one unit with a much smaller reservoir and produced approx 2.5-3.5 lbs of baby greens a week from July through to end of September so this year we decided to scale up.

Our crop this year consists of several varieties of basil, kale, mustard, lettuce and arugula as well as spinach and sorrel.

I am happy to answer any questions you may have and have some questions of my own.

1. Has anyone had problems with algae? If so, how did you know it was a problem and how did you overcome it?

I understand that algae needs nutrient rich water to be exposed to light so we have tried to light proof the garden. We are finding this difficult as the plants are still small so it is hard to place enough hydroton in each net pot to block out the light without covering the plant as well (we started from small seedlings in rockwool cubes).

Currently there is evidence of algae growing on some of the tops of the rockwool cubes that are exposed to sunlight.

2. For those using a similar design garden how did you start your plants? Did you buy them from a nursery and then wash the soil off of the roots and put directly into hydroton/net cup combo? Did you start from seeds in rockwool and then transplant into the garden?

We chose to start from seeds in rockwool cubes. Difficulty is getting seedlings to grow to sufficient size such that when they are put into the garden they are a) tall enough so that their leaves are above the PVC pipe (receive sunlight) and b) roots are long enough that they are in the stream of water at the bottom of the pipe.

As we have been unable to grow seedlings with sufficiently long roots when we transplant into the net pots we have been damming up the water in the pipes so that the roots are touching the water (this is time consuming tedious work).

Again, happy to answer any questions that you might have as well. Also if you see anything that might pose problems for us in the future we would be happy to hear this too.

Comments (4)

  • ajames54
    9 years ago

    not sure if I'm going to be a lot of help but I'll give it a go..

    Starting with question 1, there are many different types of algae VERY broadly speaking the main ones are green, blue-green, red and brown. Each of these has their own cause and cure. On my rockwool started plants I have a bit of green algae which I ignore, though cutting off the light is enough to knock it back.There are foam discs sold to keep light off the top of your pots or you can build up a layer of hydroton deep enough to not be always wet. Brown algae will react much more slowly to having its light cut off but it is usually a sign that your water is high in silica, there are special filters to remove silica that should solve the issue. True Red algae is unlikely to be an issue and I don't know what to do about it. Blue-green algae is the hardest issue to deal with. Technically it is cyanobacteria, half algae half bacteria and while most are harmless some do excrete toxins. Some can fix nitrogen out of the air if necessary and all will move to what ever light there is. The only solution I know of is to remove the infected plants and sterilize the area near them.

    for question 2 I've just finished experimenting with my own system, only 56 plants but what the heck. I tried a number of different ways to start the plants..rockwool cubes, coconut coir, paper towel and promix (dirt) I tried starting all of them in the basement under lights where I have an ebb and flow system and a DWC system. (the seeds started in Dirt were in trays).

    Starting the plants in dirt and then rinsing them before re-potting with hydroton was surprisingly the second most successful way I found for propagation. The clear winner for me though was in a strip of folded papertowel in the DWC system. Compared to them the plants started in rockwool and coir appear stunted. I think they took too long getting their roots OUT of the starting media and into the growing media.

    (Getting the seeds into the paper towel was a giant PITA though so my next experiment is to try cutting the rockwool into strips say about 1/4 inch X 1/4 inch by 2 inches)

    The plants started in the Ebb and Flow had much shorter root systems than those started in the DWC, so much shorter that I found I had to dam the 4 inch PVC pipe I used as well. The DWC starts were all more than long enough to fit into the pipe.

    Going forward I will be using the 38 liter Rubbermaid bins that I was using for DWC. Three bins will fit into a 2 foot X 4 foot space and each lid can be comfortably drilled for 15-18 2 inch pots or 12 3 inch pots.

  • Green_Guys
    Original Author
    9 years ago

    Thanks ajames54 for your reply,

    Last year we ran our garden right until the end of September. At this points most of the roots were brownish in colour and some of the plants had started to die. What would happen is that a whole plant would wilt. When we would pull the plant out there would be a strong earthy smell to the reservoir.

    At the time we thought this was due to a lack of oxygen in the nutrient solution due to warm reservoir temperatures (we had an above ground reservoir then) plus a build up of oxygen eating bacteria from dark green algae that was growing on the tops of the rockwool (we didn't use netpots last year, instead we used a home made plastic funnel that the rockwool was suspended in). We had also experimented with using water from an aquarium to provide the nutrients (a quick and failed attempt at aquaponics) prior to moving to a commercial grade fertilizer so perhaps the system could have been colonized back then by bacteria from the fish. Not sure.

    Either way we are doing our best to try and prevent our plants from dying of the same or a similar condition.

    We are about to start a new batch of seeds and are planning to put them in rockwool and then put a grow light on them 16 hours a day. Our last batch of seedlings were very leggy and only had their first set of leaves (cotyledons). We are hoping that the grow light will fix the "legginess" problem. When you transplant into your system how many sets of leaves etc do your plants typically have? How many weeks/days did it take you to grow your seedlings to the size for transplanting into your NFT system?

    Given your success with the paper towel and DWC system I am interested in how it was set up. Was it a large DWC system? How did you position the seeds?

    The attached photo shows what the roots were like at the end of the last growing season. Maybe you have seen roots that look like this or read about them?

    Cheers,

  • ajames54
    9 years ago

    The smell you describe coupled with the description certainly sounds like you had an issue with with bacteria from the aquarium. In a healthy aquarium system there are two main types of nitrifying bacteria, the first takes the ammonia from the fish waste and turns it into the less toxic (to fish) nitrite the next turns the nitrite in to harmless (to fish) nitrate. If you started with aquarium water and then switched to a commercial fert that used either ammonia or a nitrite for a Nitrogen source it is quite possible that you grew a huge batch of these bacteria. Adding another big IF to the scenario, a bacterial bloom would coat the roots use up large amounts of the available nitrogen and at least as importantly the available oxygen, making for very unhappy plants. On the fortunate side, unlike algae the bacteria does not hold firmly to what ever it is attached to and should be relatively easy to rinse off.

    This is one of the Rubbermaid bins I've been using for DWC and some seeds I started on Sunday. The light source is 4 Sunblaster CFL in a 2' x 4' area, I'm quite impressed by them, I get much better plants than I would get from my old T8 or T12 grow lights.

    Time frame really depends on the plant. I would normally move them when the second set of true leaves fully appeared, though because it was so cold for so long this year some things were more mature than that. For most things by the time the second leaves appear I've got 4 to 6 inches of very fine root out the bottom of the net pot.

    There are also a couple pepper plants that I am leaving in there to see how they do compared to those that are in the NFT and those in the Ebb and Flow.

    As for the starting, as I said it is a pain but it is working well for now while I am looking for something quicker.

    -cut a strip of paper towel 1/2 inch wide and as long as the net pot is deep.

    -dampen the paper towel and place the seed 1/8 - 1/4 inch away from one end, fold the paper towel lengthwise over the seed.

    -holding the seed, position the strip touching the bottom of the net pot, fill pot with hydroton.

    -place pot in DWC system, the bottom of the pot and the end of the paper towel should be at or just bellow the surface of the nutrient solution. (I tried this in the E&F as well, while it worked OK the DWC was better)

  • Green_Guys
    Original Author
    9 years ago

    Thanks for the information about the bacteria... I had thought that bacteria from the original aquarium water might have eaten up some/all of the oxygen. I had not thought though about the nitrogen (plant food) that it might have eaten up as well.

    Thank you as well for the further detail about how you start seedlings using the DWC and paper towel method. As I am starting 100 seeds or more at a time and live in an apartment so I don't have the space that this would require.

    Yesterday I purchased a Sunblaster 25HO (24 watts I believe?) grow light and placed it 8 inches above two trays of rockwool with seeds in them. I placed the seeds in the dry rockwool (2/hole) and then poured 1 gallon of water over each tray. A humidity hood is covering both trays and in two days I will remove the hood. Hopefully within a short period of time I will have seedlings with their second/third set of leafs. I will keep you posted.

    Cheers,