Best soil for weed plants indoors

Indoor marijuana growers face a unique dilemma when deciding how to grow their crop: should they grow in soil or in a hydroponics system?

If you haven’t before considered a hydroponics system and you have a larger budget, you may want to look into it.

Many growers opt for soil when they are starting out.

This is a good way to get to know the plant and how it functions, without over-investing in the process.

You can grow a fully biological product, and you get to take advantage of all the agricultural knowledge humans have accumulated over the last several thousand years. Pretty neat, right?

Fully biological marijuana plant
Fully biological marijuana plant

Whichever method you choose, you should do the proper amount of research to ensure that your harvest is successful.

This article covers the pros and cons of growing marijuana on soil.

Growing cannabis indoors in soil

Out in the wild, the roots of the Cannabis plant will stretch out long distances over time, seeking water and the nutrients required to thrive.

Indoor growing, however, requires a much smaller root system for both convenience and simple space required.

It’s up to the grower to make sure the plant is being supplied with adequate amounts of water and nutrients.

They just don’t have the space for expanding their root systems.

Be sure that the temperature around the roots is warm enough (~68 degrees F), that the roots are well aerated, and that the water is being cycled and drained regularly so that it won’t become stagnant.

Advantages & disadvantages of growing indoors with soil

It’s easier to irrigate plants in soil, or more forgiving at least.

You don’t need to be quite as careful as you do when watering plants in hydroponics systems.

Plus, fertilization is easier to deal with in soil.

It’s conventional, and so you can draw on a huge knowledge base. If you’re having issues, you’ll be able to troubleshoot them reliably.

Growing marijuana indoors
Growing marijuana indoors

Different soils can also impart enjoyable and unique flavors to your harvest, which can frequently be a huge plus (although not necessarily). You will also need to know the best way to germinate marijuana seeds in order to ensure your grow succeeds.

Download my FREE marijuana grow bible and start growing high quality marijuana strains.

Unfortunately, dirt is heavy, and it takes up a lot of space. This is a problem for a lot of indoor growers who only have limited space.

Plus, dirt is, well, dirty.

Your chances of getting insects or pests goes up substantially when you use a soil substrate for your Cannabis plants.

The factare, some people just aren’t gardeners.

There’s a certain sensibility that goes into planting seeds in soil and coaxing the up into beautiful towering plants.

If soil isn’t working for you, consider the finely tuned science of hydroponics systems.

Size of the containers

The size of your Cannabis plant will correlate directly to the size of its root system.

This means that the more space your plant has to expand its roots, the more easily it will grow.

containers for cannabis
Cannabis containers

If the Cannabis plant ends up being too large for the pot, you will run into issues with nutrient and water absorption. You will need to know how to transplant your weed plants.

Your plant will have a minimized efficiency, and the soil will likely burn through water quickly.

Cheap cannabis seeds are never part of our inventory. Instead, check out these great deals on the best quality feminized marijuana seeds.

Indoor marijuana seeds

Buy indoor marijuana seeds

  • Easy to grow
  • Guaranteed germination
  • Beginner friendly
  • Grow guide available

In general, if you have an average Cannabis cutting or seedling, a pot with dimensions of roughly 10x10x10 cm will be large enough for you.

If the plant has reached the height of 25-35 cm (especially if it hasn’t stopped growing), you’ll need a pot that’s roughly twice as large, around 15x15x20 cm.

If your plant grows larger than 80 cm, you’re going to need a pot that holds at least 10-12 liters.

Once the plants reach any size larger than a meter, the size of the pot increases accordingly.

Repot the plant when necessary (and carefully) as it matures. 

Remember to keep an eye on the plant as it grows. If your plant never has room to get bigger, it never will.

Marijuana Nutrients
Marijuana Nutrients

Best nutrients for growing cannabis indoors in soil

Soil contains a wide range of naturally occurring ingredients because of its organic composition.

A lot of the nutrients available in rotting vegetable matter and animal remains right away, however, requiring additional processes to break them down before they can be absorbed by the roots.

Worms and insects aid in the decomposition process, breaking down the materials into a smaller form that the plants can absorb.

Rain also helps in the decomposition process.

Water is a very effective solvent; it can dissolve materials and make them available for absorption.

Unfortunately, all of these natural processes can be difficult to duplicate for indoor growers.

How to use each nutrient with your indoor soil grow

The best bet is to start out with nutrient-rich soil and to make sure the soil has been sterilized before you begin potting your plants.

Sterilizing your soil with heat won’t guarantee that you’ve killed every possible parasite and disease, but it’s an important preventative step.

All it takes is one nasty parasite to spread around and ruin your entire crop.

You can purchase a potting soil mix at a garden shop or mix your own.

Indoor marijuana seeds

Buy cannabis nutrients

  • Fertilizer
  • Plant protector
  • Grow kits
  • Grow Guide

In either case, you’ll want to create an environment with plenty of oxygen, a temperature around ~20 degrees C, adequate water (moist but not wet), a pH value of 5.8-6.5, and plenty of nutrients.

Read the article “Measure pH and TDS of your soil” and learn how to measure the pH and TDS of your soil.

If you’re growing indoors, be careful to meet all the requirements of the soil.

The acidity, humidity, and nutrients available in an environment will determine a great deal when it comes to your plants success.

A proper pH value in your soil will maximize the absorption of nutrients.

You can use chalk and Epsom salts to change the pH of your soil.

Water retention is also very important in your soil: if your soil drains water without retaining it, your plant will get thirsty fast.

If there’s too much water, fungus could grow in the soil and damage the roots.

Consider modifying your soil with vermiculite, sphagnum moss, turf, or perlite if you want to change how your soil retains and drains water.

Learn how to harvest marijuana and protect your marijuana plants

You’ll also want to make sure you have the right amount of nutrients. Lots of nitrogen, a moderate amount of potassium and phosphor.

How to make your own indoor marijuana soil mix

One of the nicest things about soil is that you don’t need to be an expert to mix your own. It’s pretty simple, as long as you follow some basic rules about ratios.

The sort of soil you want will vary depending on the stage of growth your plant is experiencing.

For example, during the early phase of growth, you’ll want a soil mix made up of equal parts turf, perlite, and worm meal.

For growth and flowering periods, use equal parts turf, worm meal, and compost

Marijuana soil mix
Marijuana soil mix

If your pH is rising too high, you can add some chalk to bring it back down. Also, you can easily add liquid fertilizers into your plant when to water.

making your own liquid fertilizer? make sure you have it mixed well.

If the mixture isn’t well-balanced and homogenous, your plant will absorb nutrients unevenly and could experience a nutrient burn.

If you don’t feel comfortable with the idea of making your own nutrient mix, there are a number of mixes available which are specifically for the cultivation of marijuana.

Watering marijuana in soil indoors

There are no hard and fast rules when it comes to watering a marijuana plant since the requirements of the plant are determined by the environment it’s growing in.

If the environment is very hot, the plant will use more water. If the plant is receiving the maximum nutrients, it can absorb.

Watering marijuana
Watering marijuana

Water acts as a vehicle for dissolved nutrients and minerals, being absorbed through the roots before spreading through the rest of the plant.

It also cools a plant down, fills up cells to keep the plant structurally sound, and is required for photosynthesis.

In general, water enough so that your soil is faintly moist, but not wet. If the soil is too wet, you risk fungal growth and root damage.

Faq about indoor marijuana grows with soil

What are the best autoflowering strains to grow indoors?

Here is our list of top picks for indoor growing: Super Skunk Automatic, White Widow Automatic, Sour Diesel Auto, Super Silver Haze Autoflowering, and Northern Lights Automatic.

What are the best feminized strains to grow indoors?

Here is our list of top 5 fem strains to grow indoors: Blue Dream, Big Bud, THC Bomb, Chocolope, and LSD

What are the best indoor strains for yield and potency?

There are many strains that can produce high yields with great potency, here are some examples: Big Bud, Power Plant, Super Silver Haze, and Green Crack

Thanks for reading. Please leave comments or questions below and don’t forget to download my free grow bible


Avatar for Robert Bergman

Robert Bergman


Robert Bergman is an Amsterdam-based marijuana grow expert who has years of experience from small grows to massive operations ... See profile

41 comments on “Best soil for weed plants indoors”

  1. I use a mixture or vermiculite, seed raising mix and organic potting mix. I use self watering pots, that have a 1 inch gap between the bottom of the pot and the soil mix and has an opening to drain excess liquid.and I, personally, drain this everyday. These pots also make it much easier to flush your plant before harvest. The pot is mostly filled with organic potting mix and vermiculite mixture and in the centre and to a certain depth a mixture of seed raising mix and vermiculite, this is where I plant my seeds. It’s a great system, I swear by it!

  2. We want to transplant a small plant into a 10 gallon grow pot. we bought chicken. worm castings, Hydrolyzed fish fertilizer, 2-4-0. we want to mix it up in the pro mix and then transplant. is this enough for npk

  3. Hi, I’m trying to set up auto-watering for a small indoor soil situation.
    I had a constant drip feed for a portion of the last crop and it didn’t seem to love it. After researching, I read about the ‘root cycle’ whereby the roots like to alternate between being watered and access to dryness/atmospheric oxygen.

  4. I just thought about, what if you get the nutrients packs off roses when u buy roses and then when you go to water your weed soil u mix the flower nutrients in the water and then water ur weed soil?

  5. I am just getting set up for an inside grow, i have a 4/2 by 5 tent 1200 wat full spect led and have wite widow auto seeds germinating now when ready my plan is to plant them directly into 5 gallon pots any help or sugesti would Be greatly appreciated As i said i am very new to this and am only going on research i can find

  6. Carol, You should join our forum so that you can get strong grow advice from our many expert and friendly growers. 🙂

  7. Its been 4 weeks since I planted 6 seeds and all 6 have been doing great now Two of them the bottom leaves are curling what do I do

  8. I started growing inside this last year 2018 after growing outside for42 years. I have read many articles on what dirt to use but nobody has ever given a good answer. I read many articles starring run from miraclegrow potting soil so me as a non believer in What most folks say, I started growing in these potting soil. I have harvested 9 different plants and on average I get 1.5 oz to 2.5 oz. I don’t know about ph levels and things like that but I believe I get good results.

  9. Can I use any nutrients thruout my grow even if my babies r in fox farms ocean forest if so at what point should I start

    • Gary Baier,

      A hot soil like FoxFarm will contain the necessary nutrition to get you through the vegetative cycle for the most part. You need to watch your plants in order to make sure they retain a nice green color. In general we recommend that you refrain from adding nutrients in a Foxfarm soil grow until the flowering phase. This is because the FF soil has enough nutrition for 4-8 weeks depending on environment, lamp intensity and how aggressively the genetics are.

      Happy growing 🙂

  10. I’m first timer,indoor grower ,started with 4 plants ended with 2 ,both are about 3 is tall with alo t of small white flowers and seeds the other is a beautiful green plant that I love,what can I do with seedy plant.? Is it any good ? I am a Lupus patient .

    • Linfa,

      First let me say I am sorry you have Lupas. I have a close friend afflicted also.

      Cull the seedy plant if you are sure the other is a female. If one is flowering and the other is not; You may have a male and a female with seeds. I suggest you buy feminized seeds from here on out to make sure you get you medicine and I also think you should join us at and allow us to help guide you to a successful harvest.

      Pollen sacks open and produce little flowers when the pollen is spread. If the plant has seeds on it, the the plant is a female that has been pollinated or a hermaphrodire plant that produces male and female flowers. Without pictures, it is hard to tell what the pretty green without flower…is?

      Hope this helps. We would like to see you grow successfully. 🙂

  11. Thanks, Robert. My first grow wasn’t a huge success in quantity (harvested about half of what I should’ve) but it was quality &what I gained in experience & knowledge will be irreplaceable in keeping my everyday nerve pain in check. Thank you so much for helping me get back some quality of life. You truly are making the world a better place.

  12. Going to try my hand at an indoor grow using White Widow Auto. Can I Scrog or use LST to increase yields? Or should I just let it grow on its merry way?


  14. where do you get the light my windows are kind of high and no ledge how much light do they need do you buy special bulbs ?

  15. I’m so confused. I don’t even know where to start. First I THINK I downloaded your Bible. I received at least 3 messages from Robert. I see so much information and also see ADS for this Bible to download. I thought I DID that already. I DON’T KNOW.
    I have some seeds started indoors .Some are labeled with date planted and strain type also have some notes as to which soils I tried. I see itty bitty BUGS. They don’t seem to be eating the plants. Some plants are flowering. I tried trimming just 2 plants ONCE . It seemed to work and spread out a little but I am too scared to try it again. A couple plants just keeled over and died while others are hanging in there. I am also experimenting with different types of containers. I probably should have just followed YOUR step by step instructions but I think it might take me a week just to research your choice vocabulary in said articles. Like I said before I am confused and your emails are long and maybe too informative I Don’t know. Maybe I need a marijuana growers FOR DUMMIES.

  16. I’ve got two flowered plants and it seems that they have slowed in growing does this happen at the end of the life term of the plant?

    • Flintz,

      Of course plants stop growing at the end of their life cycle. Is this a trick question? LOL 🙂

      I suggest you join our support forum in order to expose yourself to many knowledgeable growers and experts willing to help you succeed. 🙂

  17. Robert,
    Thank you for all your help, since you’ve been sending me advise I’ve went from someone that wasn’t sure that I
    wanted to grow but didn’t think I could, to someone that is a little more comfortable with what I’m doing.
    I am in my fourth grow and I feel very confident that I will soon be at the end of another successful grow.
    I want to stop growing from street seeds and start with some real good Strawberry cough, Blueberry kush, and some Black and White widow.
    After this harvest, I’ll be sending you a money order or cashiers check for the afore mentioned seeds!
    Thanks again,

  18. I keep a rabbit pen on the side of my house, and was curious about using their droppings in my soil for added nutrients. They have been raised on a diet of Timothy hay, sunflower seeds, pumpkin seeds, carrot, banana, papaya and the occasional fresh watermelon or cantaloupe. Would this be an ok additive?

    • Have you done a search on the viability of using Rabbit manure on vegetables? That would be a good place to start.

      Another option would be to join the ILGM Support forum and ask the many members; Many of who grow vegetables, organically, and may have some insight to contribute to your query

    • Rabbit droppings make for excellent soil when starting. Rabbit droppings cannot burn your plants regardless of how much you use. After planting seedlings however I suggest a good nutrient based diet for the growing phase used once and week, then for the flowering phase used 3 times a week.