Medpot Minstrel: Hydroponics Medical Marijuana

Friday, May 25, 2007

How Close Should Your Light(s) Be?

Many growers of medicinal cannabis start their seedlings under fluorescent lights, since the illumination provided by this light source is gentle and perfectly adequate for germination and initial growth.

Then, when it comes time for transplanting the rooted seedlings into intermediary pots, some more intense lighting is required. So last week I moved my 15 pots into the periphery of my 600W High Pressure Sodium light, but I was sure to insert a blue-spectrum conversion bulb, since the growth stage of cannabis requires light on the blue end of the spectrum.

There are many theories as to providing lighting for growing cannabis. The mantra is often repeated—bring your light source as close as possible to the top of your plants. Use your hand as if you were testing the heat of a baby bottle. If the light burns your hand, move your light source up a notch.

I did all that and my plants still got burned! I was watering my seedlings with a half-strength nutrient mix composed of Sensi Grow Two-Part, my basic fert, B-52 an excellent B-complex vitamin, and the three root colonizers, Piranha, Tarantula, and Voodoo Juice.

I did this at four-hour intervals, so I only left my plants alone for a few hours. However, the old motor in my ventilation fan seized up and the heat of the light burned the tips of the top leaves of my young seedlings.

It is definitely not nute burn, since my nutrient mix is still at half strength. I was just about to increase it to full strength and start the week 1 regimen of growth feeding that I mentioned in last week’s posting, and then this happened.

It is a blow to your ego when you have taken every precaution possible, and then an old motor throws a wrench into the works. However, I took steps to save my investment. When you pay hundreds of dollars for premium seeds, you want to make sure that you get your money’s worth.

Instead of figuring out the distance between the young plants and the high intensity light mathematically, I went with the commonly held belief. Instead of testing the commonly held belief with my intellect, I went along with the crowd.

I know that a 600W High Pressure Sodium light generates 90,000 lumens a foot away from the source, 22,500 lumens two feet away, 9,999 lumens 3 feet away, and 6,428 lumens four feet away. Intensity equals light output divided by the distance squared.

So to figure out the lumens at five feet, I would have to divide 90,000 by five squared, or 25. So at five feet the light given off is 3600 lumens. At six feet it is 2500 lumens.

2500 lumens is the exact number that Jorge Cervantes suggests for seedlings in his “Indoor Mairjuana Horticulture.” So according to that, I should have had my seedlings six feet away from my light.

However, I placed my 15 pots around the periphery of the light, so I had them closer than that. Also, I didn’t use my head, I used the “hand test” so I brought my light source even closer to my young plants. With the fan going, it seemed cool enough under there.

The next time I’ll be sure to do the math. As is, I gave the young seedling another application of No Shock, which is an Advanced Nutrients product designed to minimize the shock of transplanting.

Also, since the extra heat dried out my grow medium between waterings and the young plants semi-wilted, I applied Revive. This is an Advanced Nutrients product engineered just for such occasions.

Revive contains super chelated micronutrients, such as iron and zinc, as well as macronutrients such as nitrogen and calcium, which are sucked up by the roots of the ailing plants and pretty soon they’re back to their vigorous former selves.

No Shock contains Golden Honey Fulvic Acid, derived from a richly organic mined substance called “leonardite,” as well as key nutrients, immune boosters, and root stimulators. If your plants have been stressed or shocked by transplanting or some other disastrous transition, No Shock will calm them down and set them back on the path of growth in no time.

Within 48 hours my 15 cannabis seedlings returned to normal with the HID light safely positioned 6 feet above the tops of the plants. Gradually, my light will be lowered to a distance of 3 feet above the plant canopy, in order to provide the 10,000 lumens of light called for by the experts for mature cannabis plants.

Ed Rosenthal took a reading at the 40th parallel and he measured 10,000 lumens in the sunlight on a clear day at noon. Why the 40th parallel, you ask? It is an imaginary line running 40 degrees above the Equator through such countries as Spain, Italy, Greece, Turkey, and comprising the border between Kansas and Nebraska in the United States.

Jorge Cervantes agrees with the 10,000 lumens prescription for adult marijuana plants. So I wonder if all those growers who claim that they bring their lights as close as possible to the tops of the plants are giving their plants too many lumens? Could some of those incidents of so-called nute burn be better explained by the proximity of high intensity lighting?

And if you nourish your plants properly with excellent plant nutrients such as the Sensi Two-Part and later Connoisseur A & B, your cannabis plants will grow thick and robust and you won’t have to be afraid of them stretching to reach the intense light.

posted by Wes @ 12:25 PM

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