Light Cycle for my Hydroponic Garden?

by Terry
(Canada)

I have a 400 watt, 8 pocket hydroponic grow system. I have the clones in there now with a fluorescent light on for 18 hrs. How soon can I put the 400 watt system on them? How many weeks should the clones be on 18 hrs before you change the hours. Thanks, Terry!

Answer: Terry- plants given 18 hours of light or more will stay in the vegetative state. Out of all the lights that would be OK to use, fluorescent lights are the weakest. Whenever I use them to light my clones, I always leave it on 24 hours a day. This will have no negative affects on the plants, and will speed up the growth under the fluorescent light. Once you switch to the 400 watt light, an 18 hour light cycle will be sufficient for the plants and will be less expensive than running it for 24 hours every day (although it is an option).

The clones can handle the 400 watt light as soon as they have roots. The issue is not really the AGE of the clone. The real issue is that the plant is used to a relatively weak source of light, and now you want to transition it to grow under a much brighter light without shocking it. Keep the 400 watt light 4 feet above the clones for three or four days, than lower the light to 3 feet for another three or four days. Finally, lower the light to 2 feet (above the clones) and keep it about two feet above the tops until the clones grow to the size you want.

With a 400 watt light, you get about 12 inches of effective light penetration. This means the first 12 inches of your plants, from their tops down, will be receiving enough light to produce high quality fruits and/or flowers. Growing plants any bigger is usually a waste, because everything under the top 12 inches will not produce much of anything anyway.

In fact, when plants get too big (which is a VERY common mistake growing indoors under lights) I end up pruning the lower section bare, leaving just the main stem. I usually do this the first or second week into the flowering cycle. I would rather have the nutrients go up the stem to leaves and flowers that are getting more of the light. This will increase your produce yield in the end.

So, you know you do not need plants bigger than 12 or 14 inches tall by the time they finish. Many plants will grow an additional 50% or so over the course of the flowering period. Therefore, if you want to end up with 12 inch tall plants, you want to start your flowering cycle with 8 inch tall clones.

So, treat your clones in the fashion I described above until they are 8 inches tall. With rooted clones under a 400 watt light, this will only take a week or 10 days. Your question is not about feeding or nutrients, so I will assume you know what to feed your clones and how strong the solution should be and how to increase the strength of the nutrient solution each week.

Once your clones are at 8 inches tall, read my page on flower forcing- it has all the information you need for cutting the light cycle and flowering your plants without making any mistakes during this critical stage. Happy Growing!