• Professor Sprout

Professor Sprout’s Indoor Soil Growing Tips



Part 1: Water Properly


The number one killer of soil grown cannabis indoors is overwatering. Many people make the mistake of treating soil like hydroponic drain-to-waste systems like coco or peat moss, and this will most assuredly lead to stunted growth and root death.


Soil is highly water retentive and needs nowhere near the amount of watering as does the aforementioned mediums. It also requires consistent moisture levels, and cannot be allowed to dry down like you can in other products.


The level of moisture you want to aim for is what you’d find in a freshly opened bag of organic garden soil - never soggy or heavy, but always slightly moist.


You can achieve the proper level of soil hydration by doing the following:

  1. Use a shower-head type watering can to evenly sprinkle the topsoil. Never use a cup or bucket to flood the soil until your container is thoroughly filled with roots.

  2. Don’t water to runoff. Water a little bit every day to keep soil moisture levels very even.

  3. Automatic dripper systems don’t work well with soil. If you must use automated watering systems, opt for Blumat drippers that “sense” the moisture levels in the soil and water only when it’s needed.

  4. Apply a thick layer of coco mulch to the top of the soil. This will retain moisture and keep the top soil from drying out, while at the same time discouraging fungus gnats and other pests from breeding in the moist topsoil. The coco will dry out quickly while maintaining even soil moisture underneath.

  5. Use lots of perlite and coarse coco to aerate your soil mixture. This will prevent your soil from becoming waterlogged and suffocating the roots if you do happen to overwater.

Part 2:  Plan Ahead


Time management is absolutely key when it comes to growing in organic soil indoors.  Things happen slowly in soil due to the time it takes the soil microbes to break down the nutrients and make them available to your plant.


You must be able to anticipate what your plant will need ahead of time, and plan accordingly.  Here are some essentials points to consider when planning your indoor with organic soil.

  1. Mix your soils and let them cook for an absolute minimum of 2 months before you plan on using them.  I mix a batch in the middle of summer and let it compost until the following year before I use it.  Two weeks before flipping to 12:12 this Purple Vegas plant (photo) was transplanted into a 10 gallon container of Professor Sprout’s mix that had been composting for 18 months.

  2. Top dress or spike your plants with dry soil amendments at least two weeks before you think the plant will need them. Some fertilizers, like blood meal, will begin to release nutrients almost immediately, but others such as feather meal and bone meal will take a couple weeks to begin breaking down and will continue doing so for months.

  3. Allow longer veg and bloom times in organic soil.  In hydroponics, results are nearly instant and growth is rapid.  In soil, it’s the microorganisms that feed your plant by breaking down the nutrients in the soil, digesting them, and releasing them back into the soil in a form that your plant can use. As such, you need to have a little more patience and give these middle-men time to do their work.  The extra time required will pay off dividends when it comes to the quality, flavor, and potency of your smoke.

  4. If your plant is beginning to look nutrient deficient, brew a compost tea and apply it as a root drench.  Compost teas rapidly accelerate the rate at which nutrients are digested by soil microbes and can be an excellent stop gap measure to keep your plants cruising along when they are short on food.

Part 3:  Use Big Containers


In order to get big yields with indoor soil grown cannabis, you’re best bet is to go big with your containers. More roots equals more shoots, and with soil, the size of the root network, when given adequate space, will almost perfectly mirror the canopy size (as above, so below).


I generally recommend a container size of absolutely no less than 7 gallons, with 10 gallons being what I use most often for 8-9 week strains, and 20 gallons for longer flowering or heavier feeding strains (like the pair of Jamaican Vacation ladies seen in the photo above). I’ll put five of these situated under a single 1000 watt HPS light, arranging them in a two back, one centre, two front configuration.


This takes some practice to time properly, however.  You don’t want soil plants to get too root bound as they will quickly begin to consume more nutrients than the soil can replenish, and you down want to have them in more soil than they can handle as overwatering and root rot become major issues. When growing for my personal flower stash I veg in 5 gallons containers and train the plants into a full and even canopy that covers my 5x5 footprint.  I then transplant into 10-20 gallon containers of fresh Professor Sprout’s Mix, and apply a healthy dose of compost tea.  I wait until I see fresh roots coming out the drain holes of the new containers (usually a week or so), defoliate, and then flip to bloom cycle.


Depending on strain, I consistently average about 1.5 pounds per light using this method with no C02 enrichment, and water only all the way to finish.  The two Jamaican Vacation plants in the photo (plus three others out of the frame) yielded just over a combined 2 pounds dry.  While that may not sound all that impressive, the quality of flowers produced with this technique is exceptional, with better resin, terpene, and cannabinoid production than anything I’ve ever grown hydroponically.  Plus it’s 100% organic, cheap to produce, and easy to maintain.

Part 4:  Become a Brewmaster with Professor Sprout’s Super Tea


No bottled bloom booster, flower enhancer, resinator or whateverthefuck the big nutrient companies are selling you at $50 a bottle will ever compete with a nice home brewed compost tea for growing massive, sticky flowers.


Here is my recipe for Professor Sprout’s super cheap, and super simple 6 ingredient super tea.  Super!

  • 3 Gallons of filtered non-chlorinated water (if you’ve got access to a fast moving stream or good well water, bonus!)

  • 3 TBSP Kelp Meal (the cheap stuff, not soluble kelp extract)  

  • 3 TBSP Alfalfa Meal

  • 3 TBSP Glacial Rock Dust

  • 1/4 Cup Molasses

  • 2.5 Cups earth worm castings or well-rotted compost

Put all the ingredients except the compost/ewc into a 5 gallon pail and mix well - don’t use a compost tea bag, just mix it all up in the water making sure to dissolve the molasses in warm non-chlorinated water before adding.


Drop in two large airstones connected to an aquarium pump and bubble the mixture for 24 hours to begin leaching the water soluble nutrients out of the meals and rock dust while saturating the water with oxygen.


After 24 hours add your compost/ewc and let bubble an additional 24 hours for a bacterial dominated vegetative tea, or 48-72 hours for a fungal dominant bloom tea.  Strain out the gunk from the bottom of the pail and set aside.  Dilute the tea 5-1 with fresh non-chlorinated water and apply liberally to your root zone.  Do this a couple of times in veg, a couple of times in bloom, immediatley after transplanting, and the day before any major defoliation.


Be sure to take the leftover gunk and mix with a gallon or two of soil, peat, or coco, and apply as a top dressing - just make sure to cover it with mulch afterwards.


You can also inoculate your foliage against pathogens by using the diluted tea as a foliar spray up to the third week of bloom.

Part 5:  Don’t Mix and Match Organic and Synthetic


Both organic and synthetic nutrients have their place in growing cannabis.  I grow with both methods, and each has it’s benefits and it’s downfalls.  The above batch of White Diesel seedlings are growing under Mars Hydro Eco 300 LEDs in recycled Professor Sprout’s mix and have just been given a dose of Professor Sprout’s Super Tea; it’s organic all the way for this crop.


Whichever method you choose, you’ll get the best results by committing to it fully, and not trying to mix and match organic and synthetic growing styles.


Organic soil based growing relies on the immense network of microbiota in the root zone.  These little beasties eat up the dead and decaying matter in the soil and transform it into plant food.  The soil is literally crawling with life, and keeping this microbiome alive and healthy with ensure the best results with organic growing.


Synthetic, soilless or hydroponic growing is rather more sterile; using salt based nutrients in ready-to-eat form to feed your plant directly without the intervention of bacteria and fungal colonies. 


These nutrient salts are rather caustic to soil based organisms and when applied to soil in large doses will tend to wipe out large populations of microbes.  Additionally, synthetic nutrients require a much lower PH to be absorbed, usually around 5.8, whereas soil likes to maintain a more neutral PH of 6.5-7.


The point being; if you try to mix and match organic and synthetic you’re trying to do two different things at once.  You’ll achieve none of the benefits of either method, while struggling to maintain balance with two systems that are largely incompatible.


Part 6: How to transplant for explosive root growth


Here’s a few tips that will help you create massive new root growth and reduce plant recovery time when transplanting.

  1. Modify your containers by adding extra drainage holes. Most plastic nursery containers don’t allow adequate drainage, leading to overly soggy soil in the bottom of your pots which creates an anaerobic environment where soil pathogens can thrive. Pop a few extra holes in there with a drill bit to ensure plenty of escape routes for excess moisture and enhanced root oxygenation.

  2. Tickle your roots. Before dropping your plant in some fresh earth give your roots a gentle tease to loosen them from their root ball (see video above). This redirects their growth out into the fresh soil. Failure to do this results in the roots continuing to wind around themselves without venturing into the new dirt. If you’ve ever dumped out your soil at the end of a harvest to find a solid block of roots in the middle with very little root growth in the outer soil, this is why.

  3. Plant your root crown slightly above the fresh soil line. When you water, the moisture will tend to run off the crown into the outer ring of fresh soil. This encourages the roots to go searching into the new soil for water and speeds up lateral root growth.

  4. Water soil to saturation with Professor Sprout’s Super Tea (see above) to give your plant a dose of root boosting growth stimulants and to reduce transplant shock. I like to dissolve a mycorrhiza fungal inoculant like Great White, Piranha, or OG BioWar in the tea just before serving to enhance phosphorus uptake (which is needed for root development).

  5. Hands off for one week. Don’t prune or defoliate or move your plants around much during the week after transplant. Once you see fresh roots popping out of the drain holes in your container you’re good to go.

Part 7:  Recycle Your Soil


These Green Dragon Plants above (Green Crack mother x Herijuana father) are being grown in recycled Professor Sprout’s mix and looking very healthy under a Hortilux 600 watt high pressure sodium bulb.


To prepare old soil for these fresh seedlings,I took previously used root balls from a Laughing Lion harvest and shook them off vigorously to dislodge the majority of the soil.  The roots were then placed in a pile with the leftover stems from the harvest and left to dry in the sun.  Once dried this pile was then burned in my outdoor fire pit.


The soil was turned over and mixed thoroughly with a pitchfork, soaked with a fresh compost tea, and then covered with black breathable landscape fabric and let to compost in the sun.


A month later the pile was mixed thoroughly again, and then using a basic soil test (the little coloured pill tests that you can get at any garden centre) was checked for levels of nitrogen, phosphorus and potassium.  In this case I found adequate levels of all macronutrients to carry these new Green Dragon plants through a full vegetative growth cycle without any additional amendments. If that turns out not to be the case for you, this is where you would supplement the soil with a little fast-release fertilizer of whatever is lacking: blood meal for nitrogen, guano for phosphorous, and ash (from the burned stems and root balls) for potassium. You can also add some dolomite lime for calcium and magnesium if you’re using reverse osmosis water. 


After mixing I let the soil compost for one additional month, after which time I added some fresh perlite and coco to improve aeration, and then planted the Green Dragon babies in 1/2 gallon containers of the recycled soil until they reached the size you see here. Two weeks before flipping to bloom they were placed in 10 gallons of fresh Professor Sprout’s mix to see them through to the end.


Hopefully these tips will help you up your soil game and having you harvesting top shelf connoisseur grade organic cannabis that will make your weed-head friends peanut butter and jealous.


DISCLAIMER: WE ARE NOT DOCTORS. THE OPINIONS AND INFORMATION PROVIDED ON THIS SITE ARE NOT MEDICAL ADVICE. THE CONTENT OF THIS WEBSITE IS INTENDED FOR LEGAL MEDICAL MARIJUANA PATIENTS, CAREGIVERS, AND LICENSED GROWERS ONLY. SEEDS ARE FOR PATIENTS 18 YEARS PLUS. KNOW AND FOLLOW YOUR LOCAL LAWS.