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Marijuana Plant Leaf Problems

Apr 19, 2020
Common Cannabis Questions

Marijuana Plant Leaf Problems

Underlying problems with a grow environment often manifest themselves first in marijuana plants’ leaves. The seeds to grow weed are very resilient, but the fully grown plants are much more sensitive and will quickly show physical signs of their inner biology. When leaves start yellowing, wilting, or dying off for no discernible reason, it’s time for growers to do some research. Most leaf problems are the result of one of three underlying issues: pH imbalances, water problems, or nutrient deficiencies or toxicities. This article will cover all three.

Signs of Dying Leaves

Don’t wait until leaves turn brittle and fall off to take action. Look for signs that the leaves are starting to struggle. These can include yellow, brown, gray, or red discoloration, curling, or drooping. In some cases, only parts of the leaves become discolored at first before the problem spreads to the rest of them.

pH Imbalances

When growers notice leaf problems, the first thing they should do is check the pH level of their soil or hydroponic nutrient solutions. If there is a pH imbalance, the plants may not be able to take up nutrients efficiently, so even if growers firmly believe that they have a nutrient deficiency or toxicity problem, they should still start by checking the pH.

Marijuana plants prefer slightly acidic soil. Plants grown in soil are happiest with a pH between 6 and 7, while those grown hydroponically prefer a pH of 5.5 to 6.5. Any lower or higher than that and they won’t be able to access the nutrients they need to grow and thrive, which will lead leaves to sicken and die.

Pure water has a pH of 7, which means it’s pH neutral. However, most growers don’t use pure, distilled water. Those who use tap water or rainwater may want to check the pH before they give it to the plants, but that’s not enough to maintain an optimal range.

Soil amendments and liquid nutrients can also alter the pH. Over time, most growers develop a good idea of how different fertilizers, plant foods, and other amendments affect pH. Novice growers can get a head start by testing their soil or hydroponic solutions before and after administering nutrients. Test the area immediately surrounding the roots to get an accurate idea of what’s going on in the plants’ immediate environments.

Most grow and garden supply stores sell pH testers. They’re affordable, easy to use, and don’t require any specialized knowledge of science. Over time, growers will develop a more intuitive idea of how changes to their feeding schedules or other aspects of their grow environments change pH and can get away with measuring it less often.

It’s best to allow the pH to fluctuate a little, as long as it stays within the plants’ optimal range. Since marijuana plants absorb nutrients at different rates depending on the soil or nutrient solution pH, these fluctuations can allow them access to more of the nutrients they need at different times in their life cycles.

Altering pH

All growers need to monitor and alter their pH throughout the plants’ growth cycles. From the time your germinated marijuana seeds are transplanted until the time you harvest your finished buds. There are a few ways to do so, depending on whether they use soil-based or hydroponic systems.

Hydroponic growers should always start by testing their nutrient solutions before they feed them to the plants. They can then use products like pH Up/Down to adjust levels until they reach the ideal range.

There are also natural means of adjusting pH. They include adding vinegar to make more acidic solutions or whisking water to add oxygen, which brings the pH level up.

Soil-based growers usually prefer to use dolomitic or calcitic lime. Dolomitic lime also has the benefit of adding calcium and magnesium to soil, which can be beneficial to plants that are also deficient in these nutrients.

Watering Problems

If the pH in a hydroponic system or garden is within an optimal range and the plant’s leaves are still dying, the next thing to check is the watering schedule. There are three common problems pertaining to water absorption in soil-based systems: waterlogging, drying out, and poor drainage.

The best way to ensure that plants grown in soil, coco coir, and other soilless media is to ensure that around 20% of the water drains off after each watering. Wait until the soil dries out before watering them again. Growers can check to see if their soil is dry by poking a finger into their pots or garden soils. If they can fit a finger in up to the top knuckle without reaching saturated soil, it’s dry enough to be watered again.

Growers can identify drainage problems by checking for root rot. This issue typically occurs when your northern lights fem or auto bruce banner (aka bruce banner autoflower) plants get waterlogged or don’t have enough access to oxygen. Clay-heavy soils are more prone to drainage problems than sandier soils and loam. They need to be amended before the growing season begins.

The best way to amend clay soil in a full garden bed is to till in organic materials like compost and well-cured manure. Container growers have less to worry about since they typically purchase soil. If they’re having drainage problems, they can mix in coarse materials like sand or gravel or simply switch to a soilless media mix. Coco coir is popular among today’s marijuana growers, in part because it is well-draining compared to soil. It can also be mixed with potting soil to improve drainage.

Water Problems in Hydroponic Systems

Overwatering and underwatering are unlikely to be problematic for hydroponic growers since they don’t water their plants. Hydroponic growers need to keep an eye on oxygen levels instead. If hydroponic plants don’t get enough oxygen, they can exhibit symptoms of waterlogging.

The best way to ensure adequate oxygenation in a hydroponic system is to use an air stone. Growers should still keep an eye out for signs of poor oxygenation, such as root rot. Root rot can affect both soil-based and hydroponic grows.

Nutrient Problems

Like all plants, marijuana plants require a diverse array of macro- and micronutrients to grow and thrive. THC weed seeds and CBD weed seeds require essentially the same nutrient ratios, even though they produce two very different types of plant medicine. The best-known of these nutrients are nitrogen, phosphorous, and potassium, which can be found in just about any fertilizer or plant food. Growers also need to ensure that their plants have access to balanced amounts of other nutrients. These include:

  • Calcium
  • Magnesium
  • Iron
  • Manganese
  • Boron
  • Zinc
  • Copper
  • And others.

To complicate matters further, marijuana plants need different concentrations of nutrients depending on what stage of growth they are in. Liquid plant foods and fertilizers formulated for marijuana cultivation are designed for seedling, vegetative, or flowering phases. Use the right ones to make sure the plants are getting everything they need throughout their life cycles.

Symptoms of Nutrient Deficiencies in Leaves

Marijuana plants’ leaves are typically the first places nutrient deficiencies start to show themselves. Look for symptoms like discoloration of old or new leaves, disfigured new growth, curled leaf margins, and leaf death.

Nutrient Lockout

Some plants experience nutrient deficiencies even when everything they need is present in the soil in sufficient quantities to support growth. If your do si dos strain plants are unable to take up nutrients from the soil or hydroponic solution, the nutrients won’t do them any good. This condition is known as a nutrient lockout.

There are two common causes of nutrient lockouts. The first is a pH imbalance. The second is nutrient saturation in the soil. Those who use chemical fertilizers with high electrical conductivity (EC) levels are more likely to experience nutrient lockouts than organic growers.

The symptoms of nutrient lockout are the same as those of nutrient deficiencies. Correcting the problem requires measuring the EC using a TDS meter. If it’s high, flush the soil to remove excess nutrients and minerals before applying a more balanced fertilizer or plant food. This should resolve the problem.

Nutrient Toxicity

Not all nutrient-related leaf problems are indicative of deficiencies. In some cases, marijuana plants receiving nutrients in excessive quantities can also experience leaf discoloration and death. The exact symptoms depend on which nutrients are excessively concentrated in the soil or hydroponic solution.

Nitrogen toxicity causes foliage to turn dark green and become soft before they brown and fall off. Manganese toxicity causes chlorosis in young leaves and a darkening of older leaves to dark orange or rusty brown. Zinc and iron toxicity cause chlorosis and small bronze or dark brown spots on the leaves.

Sulfur toxicity scorches leaf margins, reduces leaf size in new growth, and causes chlorosis. Copper and molybdenum deficiencies cause leaf discoloration. Most other nutrients do not cause leaf damage, even when they are present in elevated concentrations. They may still inhibit plant growth or cause lockouts of other essential nutrients, though, so growers shouldn’t ignore them entirely.

The Bottom Line

Growers who pay attention to marijuana plants’ leaves can tell a lot about their overall health. This careful observation allows them to catch problems with pH imbalance, watering schedule, soil drainage, and nutrient deficiencies or toxicities early, increasing the chances that they’ll be able to fix the problems in time to avoid more substantial damage. If possible, check the purple haze plants every day to look for symptoms of leaf problems like discoloration, wilting, necrosis, curling margins, and leaf death to avoid crop losses and decreased yields. Refer back to our grow guide any time you are in doubt about the health of your plants.

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