Marijuana Soil & Medium
The medium is where your marijuana plant will do its growing. Regardless of whether you are growing in soil, hydroponics or a soilless mix, any good marijuana growing medium will have good water retention and be able to keep the roots of your plant supplied with oxygen.
This section will take you through the basics of what you need to look for in good mediums for both soil and hydroponics, as well as supply a list of mediums and their properties.
As a growing medium, soil is the easiest, fastest and cheapest way to get started, but choosing the best soil for weed is an important job. It is also more manageable and forgiving than other mediums, making it perfect for the beginner grower. Many growers would argue you get the best tasting bud from a soil medium, however, soil grown plants tend to take longer and need transplanting into bigger containers once they have started which can put the plant under stress and stunt its growth.
When choosing the best soil for weed, there are a couple of things to take into consideration; the pH and the texture. Marijuana grows best in soil that is pH 6.5 to 7, allowing nutrients to be used efficiently. To check the texture, pick up a handful of moist, but not sodden soil. The texture of the soil should barely stay together when run through your hand, and feel spongy when you clench your fist. The best soil for weed will hold water, but have good drainage.
There are a number of good soil mixes available for you to buy that aren’t expensive and on the whole, shop bought mixes contain most of the nutrients needed in a marijuana growing medium. A good marijuana soil mix, like Fox Farms will need very little amending. If it is out of your price range, you can use an all-purpose soil from Wal-Mart and use the guide below to make any amendments you might need to make your medium suitable for your marijuana plant(s).
Can I use garden soil to grow marijuana?
You can use garden soil to grow marijuana, but it is highly likely that you’ll need to mix it with compost or make amendments to include all the nutrients the plant needs. Make sure you check the pH using litmus paper or a pH meter as well as the texture to see if it is suitable using the method described above.
To increase water retention to your marijuana soil add vermiculate, or increase drainage by adding perlite. If your soil is too acidic, mix in dolomite lime using 1 cup for every ¼ litre of soil to bring pH back in line. To make the soil more acidic, add coffee grounds or citrus peelings. Remember: always mix amendments into your soil when it is dry.
What can I add to my marijuana soil?
Whether you are growing organically or not, there are many products available that will help your soil have the correct texture and nutrients for a healthy marijuana grow. Below is a list of the most commonly available in the market.
Perlite – Perlite is heat expanded glass or volcanic rock and is great for water and nutrient retention as well as aiding drainage in planting mediums. It is pH neutral, so can be added to any soil. Be careful when mixing as the fine dust from Perlite can get in and damage your lungs, so wear a mask when mixing.
Vermiculate – Vermiculate is crushed volcanic rock and is great for holding nutrients and water. Vermiculate gives fine and fast draining soils body, increasing their water retention. Its pH ranges from 6 – 9.5, so will need to be checked before being added to any marijuana soil. It can retain too much water so only use with fast draining soils.
Dolomite Lime – Dolomite lime is used to increase the pH of acidic soils. As its pH is only slightly above neutral, it stabilizes the pH safely.
Guano – Guano is dried bat or bird excrement and is available as both high Nitrogen and high Phosphorous formulas. Too much Guano will burn the roots of your plants, so follow the manufacturer’s instructions.
Worm Castings – Worm castings or worm excrement are an excellent source of micronutrients and also a good supplementary source of Nitrogen that will not burn your plants. Be cautious when adding worm casting as they are heavy and restrict root growth.
Kelp Meal – Kelp Meal is dried and ground seaweed and is full of potassium. It helps with nitrogen delivery and helps resistance to disease.
Bone Meal – Bone meal is ground up bones from the slaughterhouse and is high in phosphorous. Its neutral pH and lime content offer a buffer against acidic soil. However, it can attract pests to your grow.
Coco Peat/Coir – Coco peat is made from the hair that surrounds the husk of a coconut. It is a good retainer of moisture while still draining well and is durable, rot resistant and inexpensive. It retains a good structure and has pH of 5.5 to 6.8 meaning that it can be used on its own or mixed 50/50 with soil.
There are a number of soilless mixes available for marijuana growing. Like soil, they should have a pH between 6 and 7, and a coarse but spongy texture. Many soilless mixes come without nutrients unless stated on the bag. This can be an advantage as it enables you to have greater control over the fertilization of your plants. There are many premade soilless mixes available for you to buy, you can purchase soilless components separately, and mix them yourself to create the consistency you want, mixing when the medium is dry. Below are two common soilless mixes to get you started;
40% Worm Castings
Weed grown in a hydroponic set up will grow faster than in marijuana soil, however, hydroponics are less forgiving making them more difficult to use. Unlike soil, the mediums used in hydroponics will not buffer the plant from any grower mistakes or acts of God (i.e power outages, no water supply, etc) and is there purely for root support.
When choosing a medium to use for hydroponics your decision should be based on which system you’re using. Another important consideration is whether the medium is able to hold water, but drains really well, so that it copes with constant watering. Below is a list of mediums to be used in your hydroponic system:
Rockwool – Rockwool is literally spun rock and is probably the best all round choice as a hydroponic medium. It is impossible to over water but still holds ten times the amount of water soil does, while supplying the roots with a good amount of oxygen. Rockwool needs soaking for 24hours as it has a high pH. It has no buffering capacity, so users must exercise caution when administering nutrients.
Expanded Clay Pellets (Hydroton) – Expanded clay pellets have been heated until they have expanded, leaving them with internal pockets that hold nutrients and oxygen, while still having exceptional draining capabilities. They are pH neutral and an excellent choice to be added to mediums that need extra drainage capacity.
Coco Peat/Coir – Coco peat or Coco coir is fast becoming one of the most popular mediums used within hydroponic marijuana growing. It has a the perfect pH for hydroponics at 5.5 to 6.8, has good moisture retention while draining well, and offers some of the buffering capability of soil. It can also be used across a wide rage of hydroponic systems.
Perlite – Perlite drains fast, has a neutral pH and courser types can be used in hydroponic grows. However, it has a tendancy to float and the dust particles will clog the pumps of circulating systems over time. Like Rockwool, Perlite also offers the roots no protection from nutrient solutions and is best used in conjunction with another medium.
Vermiculate – Vermiculate holds a lot of water and is best when used in conjunction with perlite. It also has excellent buffering abilities. However, the pH of vermiculate ranges from 6-9.5, so it will need adjusting before using. It also contains trace elements of magnesium (Mg) and phosphorous (P) so needs to be flushed before use.