Leaf Problems
1) Yellowing (Chlorosis) - Chlorosis is a yellowing of leaf tissue due to a lack of chlorophyll. Possible causes of chlorosis include poor drainage, damaged roots, compacted roots (see Root Bound below), high alkalinity, and nutrient deficiencies. Nutrient deficiencies may occur because there is an insufficient amount in the soil or because the nutrients are unavailable due to a high pH. **Note- Always check the pH before increasing nutrient level. In the last few weeks of flowering a yellowing of the leaves is completely normal as the plant uses up all stored nutrients.
2) Yellowing - Lower/Middle Leaves - Yellowing of the lower leaves/older growth is a sign of a possible Nitrogen (N) deficiency. Nitrogen is a transferable element (this means the plant can move it around as needed). If a plant is not receiving enough Nitrogen from the roots then it will rob Nitrogen from the older growth. Plants that are Nitrogen deficient will exhibit a lack of vigor and grow slowly resulting in a weak and stunted plant that is significantly reduced in quality and yield. In a Hydroponic system, usually the pH is too high and has locked out the available Nitrogen. In soil a yellowing of the lower leaves could also be an indication of a root bound plant (see Root Bound below).
Solution - First, check the pH, and adjust if necessary. The correct pH for marijuana is 6.3 - 6.8 in soil and 5.5 - 6.1 in a hydroponic system. Second, make sure you are giving the correct amount/type of fertilizer/nutrients. For the vegetative stage of growth marijuana needs a fertilizer/nutrient with a high Nitrogen (N) content like 2-1-1 (or 20-10-10).
3)Yellowing - Upper (New Growth) - Yellowing of the upper (new growth) of the plants could be a sign of a Sulphur (S) deficiency. Sulphur deficiency is pretty rare but usually start off as a yellowing of the entire ‘younger’ leaf including the veins. Other signs of sulfur deficiency are: Elongated roots, woody stems, and Leaf tips curling downward. **Note- Most yellowing of the upper leaves is a bleaching from being too close to the lights.
Solution - Check and adjust the pH level as necessary. Check your fertilizer/nutrient levels and make sure you are giving the correct amount/type for you particular stage of growth. Also a good test to see if your lights are too close is to put your hand between the light and the plant. If your hand gets too hot for comfort, the light is too close and needs to be moved up higher.
4) Leaf Curling Up - Leaf curling up can be a sign of a Magnesium (Mg) deficiency caused by too low of a pH level. Magnesium deficiency will show as a yellowing (which may turn brown and crispy) and interveinal (in between the veins) yellowing beginning in the older leaves. Interveinal chlorosis (yellowing) will start at the leaf tip and progressing inward between the veins. It could also be a sign of excess heat and humidity in the grow room.
Solution - Check and adjust the pH level as necessary. When the pH is not at the proper level marijuana will lose its ability to absorb some of the essential elements required for healthy growth. If you’re growing in soil Magnesium will begin to be locked out at a pH of 6.5 and lower, in hydro it starts at 5.8 and below. If the pH is correct, then add 1 teaspoon of Epsom salts per each gallon to your water. Or, to foliar feed them, add a ½ teaspoon per quart to a spray bottle. **Note- If your tap water is over 200 ppm Magnesium will be locked out due to the calcium in the water. Magnesium can get locked out by too much Calcium (Ca), Chlorine (Cl) or Ammonium Nitrogen (NH4+). If this is your problem we suggest using bottled or RO (reverse osmosis) water.
5) Leaf Curling Down - When the leaves curl under and burn at the tips and margins it’s usually a sign that the nutrient level is too high.
Solution - Check and adjust the pH level as necessary. Flush and decrease the nutrient level.
6) Droopy Leaves - Leaves that are drooping are most likely caused by over watering/under watering or lack of light.
Solution - First off, for soil, Place you finger into your soil a few inches and see if it's dry or wet. If over watering is your problem, increase the temperature and airflow to evaporate some of the excess water also you can add some h2o2 when watering to help the roots still receive O2. **Warning!- Chronic over watering can lead to soggy roots and stagnant, icky soil. if you slide the plant out of the pot to check the soil and it stinks or is soggy then transplant into fresh dry soil. For a hydroponic system, check to see if your medium is dry or wet before you water (or your pump comes on). If your medium is still pretty wet, then you are over watering and need to water less often. If your medium is very dry before watering, under watering is your problem, just water more frequently. And lastly, If lack of light is the problem, Add more light.
