How Do I Keep Cannabis Plants Healthy?

Cannabis is a strong plant that can grow in tough environments. In general, cannabis can do quite well when left to its own devices. However, this doesn’t mean that the plant doesn’t need a helping hand every now and then. Here’s more on how to keep your cannabis plant healthy, which should in turn improve both the yield and the quality of the final product.

Download Free Beginner’s Guide to Growing Cannabis

Cannabis Growing Basics: Soil & Nutrition, Water, Air, Sunlight, Humidity and Temperature

You could have the best genetics in the world, but you won’t get anywhere unless your environment is right. Cannabis needs the following to grow:

  • Soil
  • Water
  • Air
  • Sunlight
  • Humidity
  • Heat

Now let’s look at each of these in a little more depth. Cannabis grows best in the following environment:

Soil

The ideal pH to grow cannabis in is a slightly acidic soil of around 6 – 6.8. For those using soil-free methods, a pH of between 5.5 and 6.5 is ideal. Loamy soil (a mixture of sand, silt and clay) is generally best for cannabis. If you’re outdoors and there are plenty of earthworms in your soil, see this as a good sign. The ideal nitrogen:phosphorus:potassium (NPK) ratios are:

    • Early veg: 2:1:2 – 4:2:3
    • Mid-veg: 10:5:7
    • Late veg: 7:7:7
    • Early bloom (flowering): 5:7:10
    • Mid-bloom: 6:10:15
    • Mid–late bloom: 4:7:10
    • Late bloom: pH balanced flush (no nutrients)

The other nutrients a cannabis plant needs include: sulfur (S), calcium (Ca), magnesium (Mg), zinc (Zn), iron (Fe), manganese (Mn), molybdenum (Mo), copper (Cu), cobalt (Co), chlorine (Cl), silicon (Si), and boron (B).

Water

As with soil, you will need to check the pH of any water you’re using in order to ensure the plant stays healthy. It is best if any water you are using is as neutral a pH as possible, so 7.0 is ideal. If you’re in a rural area, rainwater is perhaps the best water to use, as it has a neutral pH and doesn’t contain many contaminants.

Those using tap water should let the water they use sit for 24 hours before watering in order to remove any fluoride, lime or chlorine that is used to treat the water. Take into account how soft or hard the water in your area is as well. It may be best to avoid water from wells, reservoirs or springs, as they may contain harmful bacteria, fungi, viruses or parasites.

Distilled water is the best type of water to use for most people, as it has a neutral pH, is the least likely to contain contaminants and you can add whatever nutrients you need.

Air

Cannabis likes to breathe, and the plant needs air in order to take in nutrients properly from the soil, as well as transpiration (the process of water movement through a plant and its evaporation from aerial parts, such as leaves, stems and flowers). Air can also provide the cannabis plant some resistance, allowing it to grow stronger, improving yields.

Sunlight

During the vegetative stage, your plant needs 18 hours of light and 6 hours of dark time (although some go as far as a full 24 hours of light for indoor grows, with lights being in the 125 Watts – 250 Watts range). Once the plant is in its flowering stage, it needs 12 hours of light and 12 hours of darkness, with indoor lights being between 400 Watts and 1000 Watts. Remember though that lights give off heat, so take into account the temperature of the environment before adding wattage.

Humidity

The recommended relative humidity level for a vegetating plant is between 40% and 60%. For flowering plants, a relative humidity level of 40% – 50% is ideal. If the humidity is too high, your buds are prone to rot. Too low, and the plant is prone to losing water.

Temperature

During the vegetative stage, the ideal temperature is between 70-85 degrees Fahrenheit (20-30ºC). During the flowering stage, temperatures should be kept between 65-80 degrees Fahrenheit (18-26ºC). You will need to cool down or heat up the environment if temperatures fall above or below these guidelines.

Cannabis sativa plant.

How to Tell When You Have a Nutrient Deficiency in Your Marijuana Plants

What Are the Cannabis Plant’s Primary Macronutrients?

These are the nutrients the cannabis plant needs in the largest amounts:

  • Nitrogen (N)
  • Phosphorus (P)
  • Potassium (K)

Your plant will quickly die (or just not grow at all) if there are any deficiencies in the above nutrients.

What Are the Cannabis Plant’s Secondary Macronutrients?

These are just as important to plant health as primary macronutrients, but are consumed in smaller quantities. They include:

  • Calcium (Ca)
  • Magnesium (Mg)
  • Sulfur (S)

What Are the Cannabis Plant’s Micronutrients?

Micronutrients are nutrients that are needed in smaller amounts compared to macronutrients. Micronutrient deficiencies are not necessarily as harmful as macronutrient deficiencies, but they can have a dramatic impact on the plant’s resistance to pests and disease, their overall functioning, and yield. Micronutrients include:

  • Zinc (Zn)
  • Iron (Fe)
  • Copper (Cu)
  • Manganese (Mn)
  • Molybdenum (Mo)
  • Copper (Cu)
  • Cobalt (Co)
  • Chlorine (Cl)
  • Silicon (Si)
  • Boron (B)

Mobile and Immobile Nutrients

Knowing the difference between mobile and immobile nutrients can help you spot what type of deficiency a plant is suffering from. A mobile nutrient is a nutrient that is transported to different areas of the plant as and when needed. For example, phosphorus stored in older fan leaves can be directed towards newer growth if a deficiency occurs. Deficiency of a mobile nutrient is more likely to be visible in older growth.

Immobile nutrients are nutrients that are locked in place and cannot be distributed by the plant. For example, if a zinc deficiency takes hold, the signs will first show in the newer growth as the plant can’t relocate its mineral stash.

Nitrogen, phosphorus, potassium and magnesium are mobile nutrients, and deficiencies in these minerals are more likely to show up on old leaves. Calcium, iron, manganese, boron molybdenum and zinc are immobile nutrients, and are more likely to show up on new growth. Sulfur is the only immobile nutrient that shows up on older leaves.

We’ve put together a comprehensive guide to help you identify nutrient deficiencies, preventing these deficiencies and overcoming deficiencies.

Download Free Guide to Plant Nutrients

Cannabis Plant Pests and How to Deal With Them

Prevention is better than cure when it comes to dealing with pests, and we advise using natural methods to control them wherever possible. Pesticide use should ideally be kept to a minimum or not at all. Here are some natural preventative methods:

  • Use clean soil.
  • Ensuring your plant is well-fed, receiving enough air & sunlight, and is being kept in its ideal pH of around 6-0 – 6.5 will help the plant ward of pests and diseases
  • Add mycorrhizal fungi to your soil.
  • Utilize hybrid and autoflowering strains – these are usually stronger due to their hybrid vigor.
  • Pruning – getting rid of old, diseased leaves can prevent the entire plant from becoming contaminated.
  • Planting repellent crops like basil, mint, marigolds, lavender and chrysanthemums near your cannabis plants.
  • Kill off weak plants – they are more susceptible to disease, and can pass on the problem to others.
  • Keep your grow area clean – no fallen leaves, faded blooms, weeds, and if growing indoors you don’t want soil on your floor. You want to keep the grow room as dust- and hair-free as possible.
  • Yellow sticky card insect traps – when placed on the ground and in between the shoots or branches of plants, they’ll catch many garden bugs that are traveling through your garden.
  • Using predatory insects – ladybugs are a popular choice, as a few ladybugs can eat many insects whilst leaving your plants intact. Don’t use any chemicals for 10 days before releasing these insects.
  • Practise crop rotation – move your grow to different locations to prevent bugs from attacking your plants. Crop rotation can also keep vital soil nutrients from being depleted.

You can download our comprehensive guide to cannabis plant pests to learn about the symptoms and treatment of 12 common pests.

Download Free Guide to Plant Pests
Written by
Dipak Hemraj
Dipak Hemraj

Dipak Hemraj is a published author, grower, product maker, and Leafwell’s resident cannabis expert. From botany & horticulture to culture & economics, he wishes to help educate the public on why cannabis is medicine (or a “pharmacy in a plant”) and how it can be used to treat a plethora of health problems. Dipak wants to unlock the power of the plant, and see if there are specific cannabinoid-terpene-flavonoid profiles suitable for different conditions.

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