Sick Marijuana Plants
OK, you have carefully measured and adjusted your reservoir, pH and PPM for your indoor grow but your plants look sickly. Let’s take a look at some possible causes and solutions. First review the marijuana pests & diseases article to make sure it is a nutrient deficiency issue. No critters harassing your weed? Good.
The next thing to check for is over/under-watering. This is rarely a problem for well-designed hydroponic grows. Under-watering is usually fairly easy to determine as the leaves will look lifeless and droop from the stem and may feel dry to the touch. To be sure to check your soil (or soiless mixture) with a moisture meter or stick your finger in the media. If it is dry, a good watering should bring them to back to life in a few hours.
Over-watering is very common, especially among neophytes. Marijuana likes to dry out between watering; too wet and the roots may suffocate and rot. Plump green leaves that droop from the middle may well be a symptom of too much water. If using hydroponics such as ebb and flow or drip irrigation, decrease the rate of water flow or increase the dry times between cycles. In soil and soilless grows, all you can do is wait for the plant to recover.
If your soil or water is too acidic or too alkaline, it will be difficult for you weed to absorb nutrients. Symptoms are gnarled and twisted leaves or red, brown or yellow spots. If this imbalance remains untreated it will lead to ‘nute lock-out’ and death. The solution is to check and adjust using your pH meter. More about pH is available here and here.
This is the next most common growing error. Also known as ‘nute burn’, it is easily recognized as the tips of your leaves will turn brown and dry. The plant is attempting to void the excess chemicals and minerals into the tips. Flush your plants and give them pure water for a week or so then slowly begin feeding again.
Identifying macro nutrient deficiencies
Low nitrogen is generally characterized by an even yellow or gold color of the lower sun leaves. Slow growth and undersized leaves and red stems are also clues. Adding a high nitrogen fertilizer should remedy the situation within a few days and will be accompanied by green, lush growth.
Also identified by slow growth, leaves will become a very dark green or purple color and may have red or purple veins. Leaves may be quite small and possibly deformed. Using a high P fertilizer should correct the problem.
This is tricky because your marijuana will exhibit vigorous growth so excessive height may be your first clue. Sometimes the tips of the large lower leaves will turn brown and die. Spots and areas of dead tissue (necrosis) may form on the blades, particularly on the edges. Leaves may be pale or yellow with red petioles and stems. Branches will break easily. Treat with a high K fertilizer. Recovery will be slow. New growth will not have the red color, and leaves will stop spotting after a couple of weeks.
While such deficiencies are rare, symptoms of spotting will first occur on new growth and your marijuana may appear stunted or have slow growth. Remedy by using Cal Mag. Try using tap water instead of distilled or RO water.
Deficiencies generally show on the top of the plant first. There will be a yellowing of the new leaves. Eventually the whole plant may turn a lighter green than normal. Look for pink or red coloring on the underside of the leaves. Treat with Epsom Salt.
Very rare in soil grows, symptoms of magnesium deficiency occur first on the lower leaves. The stems and petioles will turn increasingly purple. Fresh growth may appear lime green. There may be chlorosis between the veins on the leaves and the blades may begin to die and curl upwards. White leaves with green veins may be an indication of a severe deficiency. Treat with Epsom Salt and your weed will recover in under a week.
Identifying micro nutrient deficiencies
- Note that unless you are using spent or old soil or have neglected to add micronutrients to your hydroponics setup, you are unlikely to experience any of these.
Symptoms appear first on the new growing shoots. The leaves may begin turning white between the veins, which remain dark green. These tell-tale signs are most prominent on the growing shoots. Iron may be present, but insoluble if your pH is out of balance. Check and adjust before further treatment. The addition of rusty water or a commercial iron (Fe) preparation may help. Use chelated iron if your soil is excessively acidic.
A manganese deficiency may appear as chlorotic spots of leaf tissue between veins which may turn necrotic, generally appearing on the younger leaves. However, such spots may occur on the entire plant. Leaves may take on a purple and/or metallic sheen. Treat with a micronutrient blend.
Symptoms of B deficiency first appear at the growing shoots which die and turn brown or gray and may appear burned. A telltale sign of boron deficiency is that as soon as the growing tip dies, the lateral buds will start to grow, but will also die. To treat boron deficiency use one-fourth teaspoon of boric acid per quart of water. Recovery will occur in a few days with a healthy growth of new shoots.
You are very unlikely to encounter a chloride deficiency, but you will know it when the top side of mature leaves start to take on a bronze color. Tap water will cure this in short order.
Mb deficiency may be recognized by a yellowing of the leaves at the middle of the plant sometimes turning orange in extreme cases. Leaves may also appear mottled and necrotic. Treat with a micronutrient blend.
Zinc deficiency symptoms are evidenced by chlorosis of leaf tissue between the veins. These white areas start at the leaf margins and tips. Tiny new leaves may also be twisted or curled in a corkscrew. Use a commercial zinc preparation to remedy.
Cu deficiencies are rare, but may be recognized when the younger leaves appear somewhat limp and may become necrotic at the tips and edges. If you let it go too long and the whole plant will wilt.
Proper care and treatment of your weed will prevent most deficiencies. Due to human nature, nutrient toxicity or over-fertilizing, is much more common than nutrient deficiencies. Underfeed and underwater slightly, keep your pH in check, monitor regularly and you are almost guaranteed a healthy indoor marijuana garden.