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Calcium aids in the decomposition of organic matter at the root zone, facilitating nutrient absorption. Cannabis uses extra calcium in the middle of the flowering process. Depending on species, this can be from three to six weeks into flowering. The plant may display several types of nutrient problems when this happens. Calcium is essential for general plant health and stress resistance.

Calcium acts in concert with other important compounds to ensure overall plant health and vitality. A lack of calcium can mimic other deficiencies since the plant's ability to maintain essential biological functions is compromised. The following represent symptoms of a calcium deficiency: New growth at the top of the plant is primarily affected. The root system is compromised so fewer nutrients will be absorbed. Flower growth severely affected, especially at peak florescence. Young calyces are crinkled, distorted and don't fill out. Roots become brown and are susceptible to slimy root rot and other pathogens. Growing outdoors in soil generally allows for a greater margin of error with many nutrient problems. Unmodified acidic soils like those found in pinewoods can leach calcium, but proper attention can prevent calcium issues.

Modify the soil with garden lime, dolomite, powdered bones, crushed eggshells or fish meal. There is little chance of a calcium deficiency growing outdoors in pots or growbags. Contemporary soil mixes usually have a complete spectrum of vital nutrients for the life of the plant. Organic growers will have no-till winter companion plants rehabilitating the soil for the new season. Tomatoes are another plant notorious for their calcium demands. An old gardener’s trick is to dig a hole deeper than what is needed for the transplant. Put two fish heads and a palmful of garden lime in the bottom and water in. Backfill with soil, then plant the seedling as normal. Soil: Avoid calcium deficiency from the outset with good soil selection. Make your own soil or buy a commercial mix with plenty of calcium for the life of the plant. If on that rare occasion a calcium deficiency is identified, there are a number of ways to rectify the problem: Add dolomitic lime or garden lime and water in. Add a commercial calcium-magnesium solution, calcium acetate or calcium-magnesium acetate for a rapid calcium boost. Add liquid calcium, liquid lime or a teaspoon of hydrated lime dissolved in four litres of water. Check pH after treatment to make sure it is still between 6.2 and 7. Neutral mediums & hydro: Calcium problems are far more likely when variables in nutrients and the grow environment aren't buffered by active soil. Most water contains calcium, so little is added to commercial nutrient solutions. If a deficiency develops: Make a mixture of one teaspoon hydrated lime to four litres of water and water in. If your water is 150ppm (EC 0.3), then there is little risk of calcium deficiency. Using unmodified RO or distilled water can strip calcium from plants. Before making a nutrient solution, add two parts calcium to one part magnesium to the water until the ppm reading is at least 150-200 (EC 0.3-0.4). Water is one of the most important factors when growing cannabis. Always check the water before making any decisions. Fluctuations in pH can mimic many plant deficiencies and is the primary problem where plant health is concerned. Bad pH requires flushing the plants with clean water. Problem: Calcium is an important nutrient which helps provide structure to the cannabis plant and helps it withstand stress like from heat. When your plant has a calcium deficiency, the main symptom that you’ll be able to notice is brown or bronze splotches or spots on your leaves. A cannabis calcium deficiency can sometimes be difficult to diagnose since calcium deficiencies are often accompanied by magnesium, iron, and/or other cannabis deficiencies.

Calcium moves relatively slowly through the plant (it is a semi-mobile nutrient), which means it tends to “stay put” after it’s been given to a leaf. It tends to show up on leaves that are actively growing and getting some amount of light.

Calcium deficiencies most often show up in the following places: Newer growth (upper leaves) Parts of fan leaves that have been exposed to the light.


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