The most common problems are, excess water and fertilizer, followed closely by incorrect pH and tangled roots. Before any remedial attempts are made, these factors should be considered.
- Nutrient Deficiency – Rarely occur in modern gardens. What people see as nutrient deficiency, 9 out of 10 times is pH problem. A very high or very low pH blocks the plant’s ability to absorb nutrients, so they appear to be deficient when in fact there are more than enough nutrients in the solution / soil. Adding nutrients only worsens the situation by deregulating the pH even more and increasing the amount of particles in the medium.
Solution – The best thing to do, if any form of nutrient deficiency is detected, is to measure and adjust the pH.
- Excess Water – Signs of excess water include: Leaves withered, curved and yellowing. Also a good indication is the constant smell of wet soil in your greenhouse / garden.
Solution – Increase the temperature and airflow to evaporate excess water. You can also add h2O2 (Oxygenated Water) to help the roots receive oxygenation. Just do not over water, only when the soil / medium is dry. If your soil is soaked, transplant your plant to a new pot with dry, fresh soil.
- Excess Fertilizer – Signs of excess fertilizer include: Burned / dead leaves at the tips / sides and curved down.
Solution – Check and adjust to the desired pH. Rinse and lower the level of fertilizer / nutrients.
- pH Incorrect – Problems with pH can manifest in different ways, from nutrient deficiency to excess fertilizer and burned leaves.
Solution – The only way to know is to measure and adjust the pH level.
- Heat Stress – Heat stress signals closely resemble burns by nutrients, except that they occur at the top of the plant, close to the bulbs. The yellowing of the upper leaves is usually caused by the proximity of the HID bulbs.
Solution – One way to know if your plants are too close is to put the back of the hand between them and the lamp for a few minutes. If you feel a sensation of discomfort it is because they are very close and the lamp should be slightly away.
- Yellow – It happens because of lack of chlorophyll. Possible causes may be insufficient soil drainage, damaged roots, compacted roots, high alkalinity and nutrient deficiency.
Solution – Again, check pH.
** Note - In the last weeks of flowering a yellowing in the leaves is completely normal, because the plant uses all the nutrients stored.
- Yellowing on Lower and Medium Leaves – Yellowing on older leaves is possibly a sign of Nitrogen (N) deficiency. Because this is a transferable nutrient (meaning the plant can move it when needed), if a plant is not getting enough Nitrogen from the roots then it will be “stolen” from the older leaves. Plants with Nitrogen deficiency usually show lack of vigor and poor growth, resulting in a weak and atrophied plant. In Hydroponic Systems normally the pH is very high, blocking the absorption of the available Nitrogen in the solution. On soil, yellowing can also be an indication of entangled roots.
Solution – First check and adjust pH. The correct pH for cannabis is 6.3 – 6.8 when on soil and 5.5 – 6.1 when in Hydroponic System. Second, make sure you are providing the correct fertilizer / nutrient amount / type. For the vegetative stage cannabis needs a food rich in Nitrogen at the NPK rate of 2-1-1 or (10-20-10)
- Yellowing on Upper Leaves – Yellowing on new leaves may be a sign of Sulfur (S) deficiency. This deficiency is quite rare but begins with the yellowing of a whole new leaf, including the veins. Other signs are, elongated roots, stiff branches and the tip of the rolled up leaves.
Solution – Check and adjust Ph in addition to fertilizer / nutrient level to make sure you are providing the correct type / quantity for your stage growth. Test the hand and see if it is too hot.
** Note - In most cases yellowing on top leaves and caused by proximity of lamps.
- Leaves Curl up – May be a sign of Magnesium deficiency (Mg) caused by a low pH level. The lack of magnesium can also generate yellowing (with subsequent darkening and dry leaves) and yellowing between the veins, beginning at the tips of the older leaves and progressing to the center.
Solution – Check and adjust pH, since out of ideal level the marijuana plant loses the ability to absorb the essential elements required for healthy growth. If you are growing in soil, the magnesium will begin to be locked with a pH of 6.5 or lower, in hydroponics starts with 5.8 or less. If the pH is correct, then add ¼ teaspoon of Magnesium Sulphate Heptahydrate (Epsom Salt) per liter of water. Or for foliar nutrition, dilute the previous dose with 2 parts of water and periodically spray on the leaves.
** Note - If tap water is above 200 PPM, Magnesium will be trapped by excess calcium (Ca) in the water. Magnesium can be blocked by excess Ca, Chlorine (Cl) or Nitrogen Ammonia (NH4 +). If this is your problem use mineral water.
- Rolls Down – When this occurs, associated with scorched edges and margins, it is usually a sign that the nutrient level is too high.
Solution – Check and adjust the pH. Rinse and lower the nutrient level.
- Withering Leaves – Generally occurs due to excess / lack of water or low light.
Solution – When on soil, first place your finger or a moisture meter a few inches below the ground and make sure it is dry or damp. If excess water is your problem, increase the temperature and air circulation in your greenhouse to evaporate some of the excess. Add h2o2 (hydrogen peroxide) diluted with water.
** Warning! - Excessive chronic water can lead to rotten / stagnant roots and muddy soil. If you detect this problem, transplant it into a new vase with fresh, dry soil. For Hydroponic Systems, make sure the medium is moist or dry before adding water or turning on the pump. If the medium is still very humid, or very dry, you will need to check your garden more often to check the availability of water in your system. Lastly, if lack of light is your problem, add more light.
- Tangled Roots – This occurs when the roots grow larger than the pot in which they are contained. Plants whose roots are tangled exhibit atrophied growth, thin, slow and producing small “shrimp”, wilted leaves easily burned by nutrients, requiring constant water. The yellowing of the old leaves progressively rising until all the leaves dry and die, is a significant signal of this problem.
Solution – Immediate transplantation to a larger vessel. The cake recipe is, 4 liters of soil for every 30 cm in height, except in clones that can use a smaller measure.
When deliriously removing the root mass, inspect and see if the roots form a closed circle around the mass, if so, try very gently to loosen these roots from the earth mass. If the roots are very tangled then you can cut a few 1 cm slices around the dough with a sharp, sterilized instrument before placing the plant in your new pot.
** Note - Do not crush the new soil in the bottom of the new pot, let it aerate but be pockets of air so that the roots penetrate easily.
- Atrophied Roots – Slow or no growth of new leaves can be due to calcium deficiency (Ca), intoxication by Aluminum (Al), Copper (Cu), pH Acid or soil toxins.
Solution – As always, check and adjust the pH. If there is any kind of soil poisoning, then you need to rinse it thoroughly.
Trouble in the Branches
- Branch or Stem Breakage – This may happen sooner or later with anyone. This can occur by attempting to train the plant, animals dropping pots or reflectors falling on top, etc. No matter how it happened, there is only cause for panic.
Solution – Fix it no problem, make splints with ice cream sticks and fasten with crepe tape or tape. A Mc Donald’s straw cut over may be a great method of “ingesting” the stem / twig. Give it a week for the plant to recover and grow again.