Last time we found how to find the perfect pot size for autoflowering plants and now we need to see what to put in those pots.

Almost all autoflowering cannabis plants are very tough and can grow in any soil but how well they can grow and how much yield they can produce are very crucial questions to ask yourself.

Most of the commercial cross-breed hybrids are very picky, can stay very short and yield very small yields if they don’t receive adequate nutrients and aeration from that soil or soilless mix. When buying your soil/soilless mix you need to think about all the aspects that are involved in the plants well being.

Light or heavy

First thing you need to know before buying your growing medium is – autoflower plants love to grow in “airy” growing medium. Airy means that the growing medium should be very spongy and allow the root mass to penetrate it well. If the soil is not “light” enough then the roots will struggle to penetrate the ground and that will stress your plant. Heavy soil will also stress autoflower plants by not allowing the roots to get enough oxygen and not allowing the water to penetrate the soil, leaving some dry spots in the middle. If the growing mix is too “light” then roots won’t be able to hold, support the plant and it will easily roll over. Too light soil will also struggle to hold water and will dry up in short amount of time.

This means that you should look for a growing medium that is airy, but if you can’t get a hold of such a thing then ad some Perlite to increase the water drainage and root penetration.


Second thing that affects your plant is the nutrients that are in the soil.
Soilless mixes usually have almost no nutrients and you will need to ad them with fertilizers during the growth of the plant.

Soil in other hand will always have some amount of nutrient in it and you need to check the package to see what they are and how long can a plant live only on nutrient that are in the growing medium.  Usually commercial potting soil contains all the necessary nutrient and they are time released so that when your plant needs them they will become available. These mixes are very different and you need to check the label on each of them but in general a soil that contains these necessary elements like Nitrogen, Potassium and Phosphorus will be able to support and feed your plant for the first 3 to 5 weeks and you won’t need to add additional fertilized in that time period.


The third and the final thing that you need to check is the PH of that soil or soilless mix. The PH or the PH scale measures how acidic or alkaline the solution is. The PH of 7 is neutral and that means the growing solution is not either alkaline nor acidic. If the PH number is below 7 then the growing medium is acidic but if the number is above 7 then the solution is alkaline. Auto flowering cannabis plants are the same as non-auto-flowering ones and they love their growing medium to be a little acidic and the number you are looking for is somewhere between 6.2 and 6.5 but a little variation to each side should not affect your plant that much. Usually commercial soil or soilless mixes are neutral and you don’t need to worry about this factor, but you should definitely check the label of the bag to see if there isn’t something written about a lower or higher PH. But the thing about soil/soilless mixes is that they work like a buffer and they can even out the PH levels and that is why beginners should start with these growing mediums and only after you have mastered them you can move on to hydroponics.

On you can find more about autoflowering plants and PH scale 


  1. I basically learned about many of this, but never the less, I still considered it turned out beneficial. Good job!

  2. Should I use new soil for each grow? I’m fighting with a friend and he says, Just use the same soil over and I say to use new soil.

    • Hi,
      I usually get new soil for each grow but you could use the same one if you remove all the roots and feed your plants with chemical fertilizer.
      My opinion is that new soil will always be PH neutral but old growing medium could have salt buildups or PH problems so it is better to get new one for each grow!

      • I was planning on new each grow, old can go in the garden or such. I’m trying to get through the entire grow without adding anything but water (I mean normally, not absolutely). If I mix rabbit manure (N 2.4, P 1.4, K .6) in with either Miracle Gro or Fox Farms before filling 3 gallon grow bags do you think it will see me through?

  3. Been doing some research on auto-flowers and the thing that I question most is what is the absolute best medium to use from seed to harvest?

    • I think that depends on the growers experience and the growing space/conditions. For some an organic mix is the best but for others a soilless mix is better.

  4. i really need help with finding a soil with the correct PH but every place i go to the soils come out to around 8 PH. can you give me a recommendation on the name of a correct soil to buy

    • Use foxfarm soil and add perlite. Comes already PH, may be a slightly more nutrients than optimal but works fine with autos after you lighten up with the perlite.

  5. Tommythecat on

    How much soil should we use? How many inches deep should it be for roots to have adequate space? I cant find any info on the net about this..

    • Auto flowers have a big central tap-root so you should get a pot that is tall not to stun the growth.

      • thats a good to know comm, thanks. first run af and now i see why they use pots what are skinnytall 😉

  6. Jayne Hinds on

    Hi my autofkowers are not giving aroma or are sticky can you help, growing in soil lits of buds but no smell

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