Rust color spots "help"

Potassium (K)

Deficiency: Older leaves, first tips and margins, then whole leaves turn dark yellow and die. Stems become weak and often brittle. Plants become susceptible to disease. K is usually present in soil, but locked in by high salinity. Internal temperature of foliage climbs causing protein cells to burn and degrade. Excessive evaporation from leaf edges causes burning.

- Healthy dark green foliage.
- Leaves loose luster, weak srawny branches.
- Leaf margns turn rusty brown, curl up and dry.
- Older leaves yellow and develop rust colored blotches.
- Leaves curl up, rots develop, old leaves drop.
- Flowering retarded and diminished greatly.

Treat deficiency: Fertilize with complete N-P-K fertilizer. Use organic soluable potash mixed with water, but adjust the pH to 6.5 before application. Foliar feeing is not recommended.

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Magnesium (Mg)

Practical Stuff: Marijuana uses a lot of magnesium and deficiencies are common, especially in acidic (pH below 7.0) soils. Adding dolomite lime to acidic potting soils before planting will stabilize PH, plus add magnesium and calcium to the soil. Add Epsom salts with each watering to correct magnesium deficiencies if no dolomite was added when planting.

Technical Stuff: Magnesium is found as a central atom in every chlorophyll molecule and is essential to the absorption of light energy. Magnesium aids in the utilization of nutrients. It also neutralizes soil acids and toxic compounds produced by the plant.

Deficiency: Magnesium deficiency is common idoors. Lower and later middle leaves develop yellow patches between darker green veins and rusty brown spots appear on leaf margins, tips and between veins as deficiency progresses. The brownish leaf tips usually curl upward before dying. The entire plant could discolor in a few weeks and if severe turn a yellow/whitish tinge before brownig and dying. A minor deficiency causes little or no problems with growth. However, minor deficiencies escalate and cause a diminished harvest, as flowering progresses.

Most often magnesium is in the soil but unavailable to the plant because the root environment is too wet and cold or acidic and cold. Magnesium is also bound in the soild if there is an excess of potassium ammonia (nitrogen) and calcium (carbonate). Small root systems are also unable to take in enough magnesium so supply heavy demand. A high EC slows water evaporation and will also diminish magnesium availability.

Progression of deficiency symptoms at a glance:

- No deficiency symptoms are visible during the first 3-4 weeks.
- The 4th - 6th week of growth first signs of deficiency appear. Interveinal yellowing and irregular rust-brown spots appear on older and middle-age leaves. Younger leaves remain healthy.
- Leaf tips turn brown and curl upwards as defiency progresses.
- Rust-brown spots multiply and interveinal yellowing increases.
- Rust-brown spots and yellowing progress from the bottom to the top of the entire plant.
- Youngest leaves develop rust-colored spots and inverveinal yellowing.
- Leaves dry and die in extreme cases.

Treat Deficiency: by watering with two teaspoons of Epsom salts (magnesium sulfate) per gallon of water. For fastest results, spray foliage with a 2 percent solution of Epsom salts. If the deficiency progresses to the top of the plant, it will green-up there first. In 4-6days, it will start moving down the plant, turning lower leaves progressively greener. Continue regular watering schedule with Epsom salts added until symptoms totally disappear. Adding Epsom salts regularly is not necessary when fertilizer contains available magnesium. Another option is to apply magnesium sulfate monohydrate in place of Epsom salts. Add fine dolomite lime to soil and soiless mix to add a consistent supply of both calcium and magnesium over the long term. Always use the finest dolomite available.

Control the room and root zone temperatures, humidity, pH and EC of the nutrient solution. Keep root zone and nutrient solution 70-75 degrees. Keep ambient air temperature at 75 degrees day and 65 degrees at night. Use a complete fertilizer with an adequate amount of magnesium. Keep soil pH above 6.5, keep hydroponic pH above 5.5, and lower high EC for a week.

Extra magnesium in soil is generally not harmful but can inhibit calcium uptake. Signs of excess magnesium are desribed below.

Toxicity: Magnesium toxicity is rare and difficult to discern with the naked eye. If extrememly toxic, magnesium develops a conflict with other fertilizer ions, usually calcium, especially in hydroponic nutrient solutions. Toxic buildup of magnesium in soils that are able to grow marijuana is uncommon.

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klever said:

Hey Vapour,

After a bit more reading, it appears that your baby might have a magnesium deficiency instead of potassium. Here's what Jorge's book says about magnesium:



Hope that helps. Looking at your pics makes me think this is most likely the problem becuase of the upward curling leaves, and also the fact that the time frame for the deficiency to show up is right on time. Did you use any dolomite in your soil?

Click to expand...

klever said:

Hey Vapour,

After a bit more reading, it appears that your baby might have a magnesium deficiency instead of potassium. Here's what Jorge's book says about magnesium:



Hope that helps. Looking at your pics makes me think this is most likely the problem becuase of the upward curling leaves, and also the fact that the time frame for the deficiency to show up is right on time. Did you use any dolomite in your soil?

Click to expand...