3R Lighting: Tutorial--Flood and Drain Hydroponics Page 2
www.3rlighting.com/tutorial
Flood and Drain Hydroponics
Q: How often should you flood the tub and for how long?
A: It depends.
Q: You know, for a tutorial you're not a real fountain of learning.
A: Thinking for yourself is hard work--that's why so few people want to do it.
Q: There's a lot of other websites that tell me all I need to do is just give
them my credit card numbers and they will take care of everything. Why aren't
you guys like that?
A: In the 3R Lighting view of the world, we want you to have equipment and
techniques that will carry you for years and through many, many harvests.
Sometimes people only think very short term and get equipment that is only for
one fast crop. This is not the segment of the market 3R Lighting focuses on.
Q: You are just hot for making me learn something, aren't you?
A: Yup.
Q: OK, how often should that tub be flooded?
A: It depends.
Q: Uh, huh.
A: As we discussed before, the plants are transpirating water through stomate
holes in the leaves. The roots soak up the water-nutrient mix through the
roots and move it up through the plant. Water alone is evaporated out through
the leaves, leaving the nutrients behind. This process called "transpiration"
is how the plant moves nutrients inside the plant itself. All right--the key
here is that the larger the plant, the more leaf space the plant has. The more
leaf space, the more tiny breathing holes in the leaves (the holes are known as
stomates or stomata). The more stomates, the more the plant uses up more
water,
faster. So the larger the plant, the more it needs
to be watered.
Got that? Larger plants need more water.
Q: Uh, huh. Larger plants need more water.
A: Moreover, the plants spread their leaves in the sun (or growlight) to let the
light warm them. This lets the water evaporate more easily through the tiny
holes
in the undersides of the leaves, the "stomates". So the more light, and the
longer the length of the light cycle, the more evaporation. So the more light,
the more the plants need to be watered. Got that?
Q: Uh, huh. More light, more water.
A: Some growing mediums hold more water than others for longer periods of time.
Perlite drains much faster than vermiculite; grow rocks drain faster than coir.
Rockwool usually has a good average and is a popular compromise. The
technique we recommend is to try to match the drainage to how frequently you
can work the watering into your daily or weekly schedule and not just be a
servant to your plants. If you use a timer and pump combination to
automatically water your plants, life usually becomes much easier.
Look at this diagram of a basic flood and drain configuration
The timer is set to kick on the pump every so often. The pump pushes the
nutrient solution up from the tank into the grow tray through the feeder
fitting. The feeder fitting has a gasket which is held positively in place by
a nut to avoid leaks. The level of the nutrient in the grow tray is set by the
overflow fitting. When the timer kicks the pump off, the nutrient solution
drains from the grow tray though the same tube down through the pump. This is
why it's called "Flood and Drain".
Q: Does anything else keep the plant from transpirating?
The humidity of the growing space also has an effect on how fast a plant can
evaporate water. The way this usually shows up is when the humidity builds up
inside a grow room high enough so the plant has trouble pushing more water into
the air. Humidity at these high levels is an open invitation to molds,
mildews, and other problems which can be avoided a whole lot easier than it can
be fixed after you have developed a problem. The humidity can vary a whole lot
throughout the day so if you just check in the morning and at night you may not
see the problem coming. If the air in the room does not move and is still,
pockets of humidity can build up here and there.
Q: Fine, so you always have to keep an eye out for problems. Get back to the
original question. What is it? Once, twice a day, every six and a half
minutes? How often do you water in
numbers?
A: If you have seeds or starts in rockwool, probably just once a day.
If you are growing in rockwool without a growlight, say in a window, watering
by hand, you can still probably water once a day. Sometimes once every three
days, just like soil in a pot.
Add that growlight, though, and you grow a lot
faster and you water a lot more. The size of the light and how close it is to
the plant makes a big difference, but with a 1000 Watt light about 18" from the
top of the plant, a young plant will probably need to be watered about 3 times
a day. A large plant may need to be watered up to 7-9 times a day in a flood
and drain system.
To accomodate your daily or weekly schedule, you can use a lower wattage light
or move it up higher away from the plants.
N.B. if you miss just one watering, the plant may be dead by the time the next
watering comes along. This is a good reason many people use pumps and timers
to water
the plants automatically. Using a pump and timer instead of hand watering lets
you run your lights longer, closer to the plants, with larger Wattages without
so much worry and stress.
The timing of the watering also has influence.
Opinions vary, so you have to see what works best for you. Many growers set their timers to water the plants at the same time the grow lights come on in the morning or when the dawn shines on the plants. The lights take some time to warm up to full brightness, so the plants can soak up something during this time. Some people set the first watering a half hour or so before dawn to allow the growing medium to fully saturate. Some people set the first watering to hit when the lights have achieved full brightness. Which way you do it depends on your hydroponic system's characteristics and size, what you are growing, and of course, personal preference.
The stomate holes in the leaves grow smaller at night. This means less oxygen and carbon dioxide pass through these holes and there is less transpiration from the roots. There are recommendations that if you are growing tomatoes or peppers and have a calcium defficiency in the fruit, called "Blossom End Rot" that you do not feed the plants during the night cycle. If the growing medium dries out too much at night, use water only.
