Hello scottyd944
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, 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.
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 .
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).
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. Peace and i hope this may help you ! As i am unsure if that is a top or bottom leaf !
