pH Levels
Healthy plants are grown in soil or soilless mix with a pH level of around 7, which can be measured on a pH pen/meter (available from hydroponics stores for around $100). Such a pen is invaluable in growing plants indoors and allows you to monitor pH levels in both soil and water. Be sure to check the units of measure on the brand of pen you are using, as they may vary.
Check the pH of your water reservoir on a regular basis and keep it as close to pH 7 as you can. You can use pH up or pH down solutions (available at hydroponics stores) to balance your water to a reading of 7. Try not to put too much pH adjuster in the water at any one time. If you mess up and put in too much pH up, don’t put in pH down to rebalance the water. Better to drain your water and start over with clean water. Having a perfect pH of 7 isn’t useful if your solution has too many chemicals and not enough pure water. If after adding fertilizer to your water reservoir, you add pH up and then find that your final pH reading is 5.8 instead of 6.3 to 7 (the perfect range for pH) just leave things alone and go with that. If you try rebalancing with too much pH up or pH down, you may find your salts and pH meter readings are bouncing up and down and they may be unable to accurately read the final mix.
Ideally you must try to feed your plants a fertilizer and water mix that has been perfectly balanced to a pH of 6.3 to 7. Adding fertilizer to water will lower the pH of the water, so you’ll probably need to adjust it with a little pH up. Once you become familiar with the amounts of fertilizer and pH up required for your garden, start adding pH up before you add fertilizer. You will require less pH up if you add it before the fertilizer. It may require a little practice to become familiar with the levels of pH up and fertilizer required, but in time it will become second nature. A monthly check with a soil slurry will show a reading of the pH that has built up in your soil or soilless medium. Read further along this chapter for more information on how to conduct a soil slurry test.
Salts Levels
Salts levels indicate the strength of fertilizers and can be determined using an EC pen, also known as a salts meter, invaluable in growing healthy marijuana and at $100, a worthwhile purchase from the hydroponics store. EC or electrical conductivity indicates how much dissolved salt is in a given sample. That is why EC is also referred to as TDS (Total Dissolved Salts) or Salinity (the amount of salts in a solution). All nutrients are salts, so EC is the same as measuring total nutrients in a solution. The water in your reservoir should have no salts in it and thus show a 0 reading on your salts pen when tested. When fertilizer is correctly proportioned into the water reservoir your salts pen should show a reading no higher than 10 for budding plants (8 is ideal) or 14 for vegetative plants (12 is ideal). If you goof up your fertilizer mix and end up with too much fertilizer, add water to bring the salts/fertilizer level down or change the water and start over. If a slurry of one part water and one part soil tests above 5 on the salts pen, it means the plants are getting too much fertilizer. If it tests below 3, the plants are getting too little fertilizer. A slurry reading of 4 on the salts pen is perfect.
Feeding
Ever wonder why some weed is bitter and goes out all the time between puffs? The answer, in a nutshell, is fertilizer. Too much fertilizer will ruin your weed. How much and how often you feed your plants are perhaps the trickiest parts for novice growers. As I’ve mentioned, every two weeks is a good feeding schedule for indoor vegetating plants and every three weeks for indoor flowering plants.
Before testing your water pH and fertilizer levels, test your pH and salts meters for accuracy using a test solution (available at any hydroponics shop). Simply dunk your pH meter in a small glass of the pH 7 test solution and check the reading. If adjustment is needed, turn the adjustment screw on the meter until the readout number on the pen reads 7. Then you can test the pH of your water. The same goes for testing your salts meter. The correct salts test solution registers 10 on the meter. By adjusting the set screw, you can adjust your salts meter until it reads a perfect 10 in the test solution. The salts meter is much more reliable than the pH meter and keeps its settings longer between adjustments, but I still check it almost every time I use it. After testing or using your meters rinse them off in clean water before putting them away.
You are not supposed to reuse the salts and pH test solutions in case they have become contaminated. I make certain to change my testing solutions once a year.
It takes some practice to get the amount of fertilizer right, but it helps to do your experimenting outside of your water reservoir until you calculate the appropriate amounts.
I follow a simple procedure I recommend for anyone starting out. You’ll need:
• two-gallon bucket
• teaspoon
• tablespoon
• measuring cup
• two-part fertilizer formula
• salts meter
• pH meter
Then follow these steps:
1. Fill a two-gallon bucket with water from your reservoir.
2. Add one to two teaspoons of pH up and stir the water.
3. Following the directions on the label, add about three tablespoons of part one of the nutrient formula and stir.
4. Following the directions on the label, pour another three tablespoons of part two of the nutrient formula and stir.
5. Check the salts level with your salts pen. It should be between 10 and 12 parts per 1,000 (ppt), which will show as 10 or 12 on your salts meter.
6. Measure the solution in the bucket with a pH meter. The pH should be between 6.3 and 7.0 on your pH meter. If either of these numbers is not reached, simply increase the amounts of pH up and/or fertilizer until the proper numbers are obtained, keeping track of the amounts. If pH readings in your test bucket are too high, do not add pH down to the water. Simply empty the bucket and start over with a fresh two gallons of water and put in less pH up to start.
7. Once you reach the appropriate pH and salts levels, calculate how many two-gallon buckets are in your water reservoir. (In a 30-gallon reservoir, it would be 15.) Then multiply your two-gallon pH and fertilizer measurements by that number, and use a measuring cup to add the appropriate amounts of pH up and/or fertilizer to your water reservoir. Remember to always add the pH up ahead of your nutrients.
Do not expect to use the same water to fertilizer ratios when mixing bloom fertilizer as you do when mixing vegetative formula. Each fertilizer requires its own mixing ratios. After a few tries, it becomes relatively easy to get a perfect mixture of pH and nutrients.
If your fertilizer ratios are off, your plants will tell you. An unhealthy or overfertilized cannabis plant will look yellow and weak, often drooping its branches, and it might show signs of burning on the edges of its leaves, which can become reddish brown and dead looking. When a cannabis plant is seriously burned by overfertilizing, its leaves might become pock marked with dead patches. Underfeeding is sometimes indicated by red stems and branches, but when cannabis leaves turn red it is usually a genetic trait and not a sign of distress.
If your plants show any of these symptoms, or after several feedings you should test the pH and fertilizer/salts levels of the soil in your plant pots by making a soil slurry. Think of the soil slurry as a thermometer that measures the health of your plants. To make a slurry you mix one part of pH 7 room temperature water and one part soil until the soil has the consistency of molasses. Take the soil sample from the rootball of the plant rather than the surface of the plant pot, and don’t worry about tearing a few root hairs out in the process. Let the solution stand for several minutes; then strain the mix through a coffee filter and place your salts meter into the slurry to take a reading. If your salts reading is 4–6, your soil has the perfect amount of fertilizer.