Medpot Minstrel: Hydroponics Medical Marijuana

Thursday, January 25, 2007


Starting a New Batch from Seed

You might have read an earlier posting in which I discussed the difficulties of my attempting to grow from clones. Being a very small medpot grower (I grow six female plants at a time under one 600W High Pressure Sodium light), the logistics of choosing a Mother Plant and isolating it on a different cycle from the rest of my ladies were baffling.

So I’m relying on my tried and true propagation method—growing from seed. I ordered ten Northern Flame seeds in a packet, since both Claire and I love the taste of this medicine. Since I normally start with 15 seeds, I also ordered 5 Afghani seeds, which were more expensive.

My freelance work has been scaled down by my clients, and as a result I’m working on a very tight budget. When you pay good money for your seeds, you want to make sure that they all germinate. So I was very careful in following the steps I usually take to germinate my seeds in rockwool cubes.

First, I soak the cubes in tap water overnight in a utility bucket. It’s important to do this overnight, to allow for the chlorine in the tap water to rise to the top of the bucket, so it doesn’t contaminate the germinating cubes.

In addition to the tap water, I normally mix in my basic fert at one-quarter its normal strength. So I mix in Sensi Grow A at one-quarter of what it reads on the bottle and Sensi Grow B, also at that reduced strength. I wait for the nutrients to dissolve. It is very important that these steps not be rushed.

Then I take a CF or a EC reading (Conductivity Factor-Electrical Conductivity). The recommended TDS (Total Dissolved Solids) level for pre-soaking rockwool cubes is 560 to 840 ppm, or CF 8-12, which is the same as CE 0.8 to 1.2. A CE 1 reading (same as CF 10) would mean that the solution is at 700 parts per million, which would be ideal for the pre-soak.

Then I take a pH reading. The ideal pH for pre-soaking rockwool is 5.5 pH, a tiny bit lower than the nutrient solution suggested pH for cannabis hydro grows (5.6 pH). The reason for the lower pH reading is that rockwool tends to be slightly alkaline, so this counteracts that bias.

If you get a reading lower than 5.5, very carefully add a small amount of pH Up, if the reading is higher than 5.5, conversely add a bit of pH Down. These agents tend to be aggressive, so they should be handled with care.

Never mix pH Up or pH Down at the same time—avoid this mistake at all costs. The chemical reaction would be totally unpredictable, and possibly violent.

Once all this measuring and pre-soaking is done, I take the rockwool cubes out of the solution and give each of them a light squeeze. This is done to reduce the moisture content by 10% to allow for air to penetrate the grow medium. The seeds that you put into the cubes need to breathe.

I use toothpicks all the time after meals—here’s another use for them. I use this very useful teeth cleaning tool to puncture a hole in the center of the rockwool, about 5mm deep. This is where I place my seeds very carefully, with tweezers.

I gently cover the hole with the material, but not too tightly. This creates a cocoon around the seed, with adequate moisture and nutrients and some air, a recipe for germination if there ever was one.

Depending on the variables, the seeds can take anywhere from twelve hours to twelve days to germinate, under a fluorescent grow light. The color spectrum of these tubes favors the blue end, which is as close to sunlight as you can get for this process.

The desired temperature for cannabis germination is around 23º C with the humidity level at 70-90%. I place my rockwool cubes into a tray with a transparent plastic lid to seal in the humidity.

Once the seeds are germinated, I have to be careful not to allow the humidity to reach 100%, so once in a while I take the lid off to allow for air circulation between the lights and the cubes.

Except this time my Northern Flame seeds germinated within a day or two, but the Afghani seeds wouldn’t budge. I waited and waited and waited. I must confess I didn’t have the patience to wait a full 12 days, so after a week or so I took the cubes with the Afghani seeds out, and removed the seeds very carefully, again with tweezers.

Plan B was to resort to that all-time favorite—putting the seeds between wet paper towels. I put these sandwiched paper towels between two large square plastic plates and made sure the edges were joined together to seal in the humidity.

I checked each day, making sure that the towels never dried out. After four days my Afghani seeds split open and sprouted tap roots, much to my relief. I placed these newly sprouted seeds back into the rockwool cubes where they came from and proceeded to wait for the formation of the first true leaves.

As more and more roots develop through the one-inch rockwool cubes, I usually transplant all my tiny seedlings into three-inch rockwool cubes, making sure that I’m very careful and gentle with these fledgling cannabis “kids.”
Eventually, when they look strong enough, I transplant a second time into six inch pots with a mixture of peat and perlite. I leave the rockwool attached to the roots, since it will disintegrate with time. These six-inch pots are then moved from the fluorescent environment to be under my 600W HPS light and an 18-hour a day, growth phase lighting regimen.

To reduce shock, it is advisable to move the seedlings slowly from one environment to another and to “harden” them by taking the lid off for longer and longer periods to enable them to get used to less and less humidity, then to place the six-inch pots around the periphery of the 600W light to begin with.

Advanced Nutrients makes two products that can be used at this time, No Shock and Jump Start, which are both designed to reduce seedling stress and to boost root and seedling growth at this crucial stage of the plant’s life.

A spray with Scorpion Juice when they’re a bit older will establish induced systemic resistance to many pathogens and pests.

With time, the six-inch pots can be moved toward the center of the powerful light and the selection process can begin. But that will be the topic of my next posting.

posted by Wes @ 10:45 PM

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