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Optimizing Vegetative Growth

Updated: Oct 7, 2021

Whether you germinated seeds to grow healthy seedlings or propagated clones from a mother plant, optimizing your plants' vegetative growth cycle is important to the final outcome at harvest, both for quality and yield.


As is always the case when growing cannabis indoors, control of environment is critical to optimizing vegetative growth. The controlled parameters are air temperature, humidity, and light. Temperature should be maintained between 60 and 80 degrees Fahrenheit, relative humidity at 60 percent, and light should be high intensity fluorescent (T5 HO) maintained within 6 inches of the tops of growing plants.

There are no excuses or workarounds for poor environment. When attempting to grow cannabis indoors, success depends upon maintaining the proper environment. While our favorite plant may be able to withstand many abuses and survive in many conditions, our goal is to help our plants thrive, not merely survive. Creating a suitable environment requires some basic skills, common sense, and almost certainly requires some spending. Spending money on good environmental control is never wasted - don’t cut corners. Take care of your environment first. Do not add plants to a garden that is has not been properly set up and tested for temperature and humidity over a period of a few days and nights. Don’t even think of asking Uncle Pete for cuts or plants unless you have a garden in which they can thrive. We don’t have an endless supply and we expect our members to be successful!


While there are many ways to grow cannabis, Uncle Pete's methods are tried and true - proven over many years. He prefers 24 hours of light for vegetative growth for its simplicity and growth rate. There are many treatises which argue that the plant must rest and sleep…don't believe it. While the indoor gardener can manipulate plant growth extensively using photoperiod, even confusing it into maturing early, these techniques are nothing more than fun in Uncle Pete’s opinion - there is always a trade off in growth rate or yield at harvest. After all is said and done, 24 hours of light for vegetative growth is the best use of time and electricity for the indoor gardener.

For early vegetative growth of cannabis plants, large, high-intensity fluorescent lights such as 4-foot, 8-lamp high-output T5s are generally the best choice. These T5 HO fixtures spread an even light for vigorous plant growth without adding the heat of larger high-intensity discharge (HID) lamps. Use lamps with a color temperature in the 5000-6400k range (cool white or daylight).

Later vegetative growth (if needed for very large plants) is best under a 1000 watt double-ended (DE) HID fixture such as those produced by Gavita or Nanolux. Smaller wattage is better suited for lower ceilings. Uncle Pete has 10-foot ceilings, but with an 8-foot ceiling, 600 watt lights are recommended instead.


Following our organic grow formula below and paying close attention to pH are the keys to optimizing vegetative growth - once the proper environment is established. Nutrient lockout from a pH which is too high or low is the number one reason for non-environmental failure. Topping, pruning, lollipopping, and other yield-enhancement techniques vary by grower and strain, even when we share the same philosophy and training. We are all unique in this way as gardeners, and several techniques for optimizing yield with training and pruning are covered in the intermediate topic Pruning And Training To Maximize Yield.

Uncle Pete's Organic Grow Formula

Transplanting from fresh clones or seedlings:

  1. Transplant into 1 or 2 gallon containers filled with Pro-Mix only, no added nutrients.

  2. Feed with pH adjusted water (5.7 - 6.0) with 1/2 teaspoon per gallon of Myco Madness.

Transplanting from 1 or 2 gallon containers:

  1. Fill 5-20 gallon containers with Pro-Mix.

  2. Add heaping 1/2 cup of Rainbow Grow per 5 gallons.

  3. Add 1 cup of worm castings per 5 gallons (when available).

  4. Mix added nutrients in well.

  5. Transplant.

  6. Feed with pH adjusted water (5.7 - 6.0) with 1/2 teaspoon per gallon of Myco Madness.

Vegetative Feeding Solution (4 gallons)

Adjust pH to 5.5, feed on Monday and Wednesday only. Do not save excess solution.

Watering Solution (4 gallons)

Adjust pH to 6.0, water on Friday only. Do not save excess solution.

  1. 20 ml Molasses

  2. 1/4 tsp Myco Madness

Target feed rates for Monday/Wednesday:

  1. 1 gallon pot - 1/3 gallon

  2. 2 gallon pot - 1/2 gallon

  3. 5+ gallon pots - 2 gallons per 5 gallons of container

The size of container you choose for your plants should be based on the final size of the plants and the number of plants under each light, allowing the plants to dry the Pro-Mix substantially, but not completely, between each application.

On Monday and Wednesday, lift each pot before feeding to check its moisture level. If the pot is still heavy, feed less. If the pot is very light, feed a little more. On Fridays use the watering solution described above to slowly and thoroughly drench each pot until there is a small amount of runoff. Read the basic topic Avoiding Water Stress for more details and tips.

Treating Problems

Common sense goes a long way during the vegetative cycle. It is easy to tell when our plants are happy, sad, or anywhere in between. While many instructor's programs go into great detail regarding nutrient deficiencies, the bottom line is that most gardeners get lost in a cycle of over correcting or fixing things that are not wrong. Uncle Pete's organic grow formula below keeps things simple - if you find a plant that is turning yellow, getting nasty in any way, or generally not happy, the treatment is always the same.

  1. Flush the plant with pH adjusted water (5.7 - 6.0).

  2. Set the plant in the “penalty box” by putting on the outside edge of the light. We don't want to put large demands on a sick plant to perform under high-intensity lights while it is sick.

  3. Give the plant a week to correct, monitoring its health.

  4. Put the plant back under high-intensity light if it is happy. Kill it, or repeat steps 1-3, if not. It is less wasteful to kill a plant during vegetative growth than during a failing flowering period after additional time under expensive lighting.

Uncle Pete likes to keep all plants clean of yellowing leaves and anything that is not green and pretty. This should not be an issue during vegetative growth. If it is, address it. By keeping the garden area and plants clean, it is simple to see new issues - regardless of how big or small they may be. A grow cannot be too clean or too organized. These simple steps make a big difference in our ability as a gardener to do the job well. Pay attention to the small details. Spend some time with your plants. Keep things pretty like someone important is coming to see your garden. Always take the extra moment to do things well.

Nothing replaces experience. If you manage to screw things up, don’t fight the plant for too long. Kill it and start again. Failure is how we learn sometimes. There is no way to instill experience in a new gardener. Get your feet wet and your hands dirty.



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