Marijuana Horticulture: The Indoor/Outdoor Medical Grower's Bible

bud. Light burn could be mistaken for overfertilization or fungus. The dead foliage makes a perfect place for bud mold to start!

Water and heat stress caused our little “Lolita” to dwarf. The roots cooked in the hot sun which arrested development.

Leaf fringe standing up – Leaf fringes that point up mean the leaf is trying to dissipate as much moisture as possible, but it is unable to. This could be caused by toxic salt buildup, lack of water, or heat stress.
    Incorrect pH contributes to most serious nutrient disorders in organic-soil gardens. Many complex biological processes occur between organic fertilizers and the soil during nutrient uptake. The pH is critical to the livelihood of these activities. When the pH fluctuates in a hydroponic garden, the nutrients are still available in the solution for uptake, and the pH is not as critical. Electrical conductivity is the most critical indicator of plant health and nutrient uptake in hydroponics.
    Once a plant shows symptoms, it has already undergone severe nutritional stress. It will take time for the plant to resume vigorous growth. Correct identification of each symptom as soon as it occurs is essential to help plants retain vigor. Indoor, greenhouse, and some outdoor marijuana crops are harvested so fast that plants do not have time to recover from nutrient imbalances. One small imbalance could cost a week of growth. That could be more than 10 percent of the plant’s life!

Here is another prime example of heat stress coupled with salt buildup and a lack of Zn, Fe, and Mn.

Big ridges between veins along with curled leaf fringes signify temperature stress coupled with salt build up.
    Do not confuse nutrient deficiencies or toxicities with insect and disease damage or poor cultural practices.
    The temperature within the leaves can climb to an excess of 110°F (43°C). It happens easily because the leaves store the heat radiated by the lamp. At 110°F (43°C), the internal chemistry of a marijuana leaf is disrupted. The manufactured proteins are broken down and become unavailable to the plant. As the internal temperature of the leaves climbs, they are forced to use and evaporate more water. About 70 percent of the plant’s energy is used in this process.
    The basic elements of the environment must be checked and maintained at specific levels to avoid problems. Check each of the vital signs–air, light, soil, water, temperature, humidity, etc-and fine-tune the environment, especially ventilation, before deciding that plants are nutrient deficient.
    Nutrient deficiencies are less common when using fresh potting soil fortified with micronutrients. If the soil or water supply is acidic, add dolomite lime to buffer the soil pH and to keep it sweet. Avoid nutrient problems by using fresh planting mix, clean water, and a complete nutrient solution. Maintain the EC and pH at proper levels, and flush the system with mild nutrient solution every four weeks.
     
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COMMON CULTURAL PROBLEMS
    Here is a short list of some of the most common cultural problems. Some of them result in nutrient deficiencies.
Lack of ventilation: Leaves are stifled and unable to function, causing slow growth and poor consumption of water and nutrients.
Lack of light: Nutrients are used poorly, photosynthesis is slow, stems stretch, and growth is scrawny.
Humidity: High humidity causes the plants to use less water and more nutrients. Growth is slow because stomata are not able to open and increase the transpiration. Low humidity stresses the plants because they use too much water.
Temperature: Both low and high temperatures slow the growth of plants. Large fluctuations in temperature–more than 15 to 20°F (8 to 10°C)-causes slow growth and slows the plant’s process.
Spray application damage: Sprays are phytotoxic, and they can burn the foliage if the spray is too concentrated or if sprayed during the heat of the day.
Ozone damage: See Chapter Thirteen “Air” for more information on ozone damage.
Overwatering: Soggy soil causes a menagerie of problems. It cuts the air from the roots, which retards the nutrient intake. The plant’s defenses weaken. Roots rot when severe.
Underwatering: Dry soil causes nutrient transport to slow severely. It causes nutrient deficiencies and sick foliage, and the roots die.
Light burn: Burned foliage is susceptible to pest and disease attack.
Indoor air pollution: This causes very difficult-to-solve plant problems. Always be aware of chemicals