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9 Common Marijuana Growing Mistakes and How to Fix Them

9 Common Marijuana Growing Mistakes and How to Fix Them

Marijuana is a weed, right? So growing weed should be easy. Just throw a few seeds in the ground, add water, wait a few months and smoke up a fat harvest.Healthy Cannabis HarvestWouldn’t that be nice? If you’ve ever grown your own plants, you know that growing marijuana just isn’t that simple. And growing good marijuana with a high yielding harvest and resinous buds is even harder. There are a slew of problems that can arise with your crop throughout the entire grow cycle. Often identifying the problem is difficult, let alone fixing it.

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We’ve compiled 9 of the most common marijuana growing mistakes in this article, and we’ll tell you how to diagnose and fix them too.

1. Nutrient Burn

Marijuana Plant with Nutrient Burn

How to tell if your marijuana plants have nutrient burn:

You’ve been trying to feed your plants properly to get a great harvest. If you’ve overfed, the excess nitrogen will be taken up the roots and cause the leaves to yellow or become “fried” looking on the edges.If your plant has nutrient burn its leaves will be affected from the outside edges and tips inward.

What to do about nutrient burn:

  • Stop feeding nutrients. Give your plants plain old water (pH balanced if you are using a hydroponic system) until the old nutrients are used up.
  • Resume feeding gradually. When you start adding nutrients again, do so slowly. Keep a close eye on your plants for signs of burning.
  • Don’t expect the yellowed leaves to recover. Any new leaves the plants grow should be green, but the damaged leaves will stay yellow.

2. Bud Rot or Mold

Marijuana Plant with Bud Rot

How to tell if your marijuana plants have bud rot:

This one is easy. Early on the buds start to dry out and look powdery. Parts of the bud will become discolored and begin to dry up. As bud rot advances the whole bud will become dark and split open, revealing dusty fungus spores. You may also see web-like white mold on the buds.

What to do about bud rot:

  • Remove all affected buds. This is critical. Bud rot is contagious, and if you don’t cut it all away your plants will all become affected. Be careful in this step- don’t let the infected buds touch any other plants and wash your hands well afterwards.
  • Ensure adequate air circulation. Good ventilation will prevent rot.
  • Avoid dampness or wetness. Control the humidity during flowering, and don’t let the buds stay wet for any length of time.

3. Heat Stress

Marijuana Plant with Heat Stress

How to tell if your marijuana plants have heat stress:

The leaves closest to the lights will begin to burn. This starts along the edges of the leaves with a thin brown or yellow line. Sometimes the leaves will curl up like a taco, or have strangely placed spots on the leaves.

What to do about heat stress:

This is the easiest problem to fix. Move the plants away from the heat source.To avoid heat stress in the first place:
  • Keep HID lights high above plants.
  • Use Full Spectrum LED lights which don’t get hot.
  • Make sure there is lots of good ventilation. Use fans if necessary.

4. Overwatering

Overwatered Marijuana PlantHow to tell if you’re overwatering your marijuana plants:This is common beginner’s mistake. Remember that a plant’s roots need oxygen to breath, and they can’t get if they are waterlogged.Overwatered plants will wilt and their leaves will turn yellow and droop. They may also stop growing and begin to die.

What to do about overwatering:

  • Stop watering. Obviously the first step is to let the plant dry out.
  • Learn the weight of your containers. Pick up your containers when the soil is dry, and again when it is well watered. With a little practice you can tell when the soil is dry by weight alone.
  • Watch for signs of root rot. If a plant has been overwatered for a long time, the roots can begin to rot. If you correct the watering schedule and your plants continue not to thrive, consider root rot as the culprit. The roots turn brown and slimy. It is hard to fix, and many people throw the plants out and start anew. You can try a product called Aquashield which is known to help correct the problem and encourage new root growth.

5. Phosphorus Deficiency

Marijuana Plant with a Phosphorus Deficiency

How to tell if your marijuana plants have a phosphorus deficiency:

There are a variety of symptoms a plant with phosphorus deficiency may display:
  • Usually the lower and older leaves are affected
  • Leaves turn yellow
  • Leaves turn dark green or blue and shiny
  • Leaves thicken and feel stiff
  • Bronze, brown or purple splotches appear on leaves
  • Leaf stems turn red or purple

What to do about a phosphorus deficiency:

  • Feed more phosphorus. Look for nutrients with a higher phosphorus content.
  • Feed extra phosphorus during flowering. Cannabis needs extra phosphorus during the flowering stage. Look for a nutrient blend formulated for flowering, or one that has a N-P-K ratio of 6-15-10.

6. Magnesium Deficiency

Marijuana Plant with a Magnesium Deficiency

How to tell if your marijuana plants have a magnesium deficiency:

Magnesium deficiencies are very common in marijuana plants. The leaves will turn yellow and later fade, but the veins of the affected leaves will remain green.

What to do about a magnesium deficiency:

  • Feed more magnesium. Magnesium is a mobile nutrient, meaning it can move about the plant. It is essential for mobilizing phosphorus.

Sources of magnesium include:

  • Epsom salts
  • Dolomite lime
  • Magnesium sulfate
  • Garden lime
  • Worm castings

7. Zinc Deficiency

Marijuana Plant with a Zinc Deficiency

How to tell if your marijuana plants have a zinc deficiency:

If your cannabis plants have a zinc deficiency, the tips of the leaves will begin to turn bright yellow. Leaf blades will also crumple and form clumps of gnarly looking, twisted leaves.

What to do about a zinc deficiency:

  • Manage your pH. If the pH is too high or too low, your plants can’t utilize zinc. You can feed all the extra zinc you like, but if your pH is out of whack, you’re plants won’t be able to absorb it.
  • Feed more zinc. There are several ways to do this:
    • Zinc oxide
    • Chelated zinc
    • Micro mix of iron, zinc and manganese
    • Zinc sulfate

8. Fungus Gnats

Marijuana Fungus Gnats

How to tell if your grow room has fungus gnats:

These obnoxious tiny black bugs will be crawling and buzzing around the soil. Your plants may still look healthy, but these bugs are a sign that you have a moisture and mold problem. You need to get rid of the gnats before they spread the fungus to your other plants.

What to do about fungus gnats:

  • Let the top inch of soil dry out between waterings. The gnats need moisture to thrive. They burrow through the soil and feed on your plant’s roots.
  • Use a fan to dry out the top inch of soil. Circulating air near the level of the soil will help it dry quickly.
  • Apply a pest treatment. Typically a single application of the Bacillus thuringiensis bacteria will get rid of fungus gnats quickly.

9. Hermies and Male Plants

Hermaphrodite Marijuana Plant

How to tell if you have hermies or male plants:

At about 4-6 weeks of age you can tell male from female plants by looking at their pre-flowers. Females have delicate white filamentous pistils, while males have a banana with two sacs beneath it.A hermaphrodite will develop both. The male pollen sacs can develop even after full flowering has begun.For more information on identifying male plants and hermaphrodites check out our page on marijuana sexing here.

What to do about hermies and male plants:

  • Kill any males or hermies as soon as you identify them. This will prevent pollination of your females so you don’t end up with seeds in your bud.
  • Avoid creating hermies. While you can’t always control this, as cannabis is a persistent plant that wants to reproduce, you can reduce your risk of creating hermies by:
    • Avoid inconsistent light schedules during flowering
    • Adjust temperature at night. Your grow room should be 10-20 degrees cooler at night, and not over 85° F during the day.
    • Avoid nutrient burn, heat stress or other conditions that will stress your plants
    • Use good quality genetics. Buy seeds from a well-respected seedbank.

Some of the worst marijuana growing problems

These are just a few of the many problems that can arise in any marijuana grow. Remember that the most important key to keeping your plants healthy is to avoid stress. You can do this by properly managing the temperature and humidity of the grow room, providing good ventilation, feeding and watering carefully and paying close attention to your plants. They will tell you when they are sick or not thriving. Notice their symptoms as early as possible. It is much easier to correct all marijuana growing problems if you catch it earlier than later. For more about pests and disease attacking your marijuana plants read here.