Collected Q&A from Readers’ Emails, Part 6

Warm Water

1. I’m having a really hard time regulating the water temperature on my hydro system. I’ve even gone as far as running the reservoir water through a coolant system (homemade of course; mini fridge) back into the reservoir, but it still gets way too warm. Do you have any suggestions that might help me regulate water temp?

I am sympathetic. This is a common problem and one that frustrates many growers. If you want to avoid buying an expensive chiller, you can coil your line inside the fridge. The more coils, the better the heat exchange (copper is a good choice for this). You can also try using a less powerful pump (one that doesn’t get as hot) and using a heat sink, for example, by setting your system on a concrete floor.

Watering

2. Without overwatering, how do you tell it’s time to water when growing in soil?

You can pick up the pot and judge by weight or you can watch for the edge of the soil to pull away from the pot slightly. Both work. Both require a little practice. When you do water, water until you get just a little runoff out the bottom of the pot—no more, no less. You will find that you get into a rhythm, watering every 2-3 days or so until the plant’s surface area explodes during flowering, at which time your watering pace will pick up dramatically.

Room Size

3. What is an appropriate room size to grow six plants in? Will it be the same regardless of growing medium?

This depends on the size of plants you wish to grow. I prefer 4’x4’ of space per plant, one light per 4’x4’ space. Yes, my recommendation is the same no matter your medium and this rule of thumb holds for both home and commercial operations.

Stabilizing a Strain

4. How many times do I have to pollenate until I have created a stable strain?

I think you are asking, “how many generations must I breed until I have created a stable strain?” The answer depends on the number of traits you are breeding for and how you are breeding. If you are growing many plants and simply want to weed out the undesirable plants before they can set seed, and allow the desirable ones (whatever “desirable” means for you—and you must have goals) to cross until they are uniform in key traits (tall, high yielding, early finish, etc.) the answer is six to seven generations per trait. This assumes you will be roughly halving your percentage of undesirable plants each generation: 50, 25, 12.5, 6.25, 3.125, 1.6. At the sixth generation you will be 99.98% free of bad plants. Then you will concentrate on your next trait, going through the same halving process.

However, this is probably not what you are doing because it is not practical to grow many cannabis plants at home, nor is it desirable to open pollenate cannabis, as seeds ruin the product. You are probably doing controlled hybrid crosses. If your only objective is to breed for one trait, and you are doing simple hybrid crosses, you can do this more quickly by backcrossing your offspring with your parent plants in order to determine the source of your offsprings’ alleles. When you have done this properly you can predict the percentages of traits inherited by the offspring before they even grow. You will need to know how to work Punnett Squares, have a good eye and keep excellent records. I explain how to do this, with examples, in my latest book, Marijuana Cultivation Reconsidered.

Author’s Note: These questions originally appeared in my column in the December issue of Sativa Magazine.

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