Calcium and Cannabis Plants

Calcium helps cannabis plants build strong cell walls, move nutrients around and grow sturdy stems and branches. You can supply it through organic amendments, commercial supplements or a hydroponic nutrient solution, as long as your pH lets the roots take it up. Kind Seed Co covers what calcium does, where to get it and how to keep levels right in your grow.

This guide focuses on calcium’s role and sources. If your plants already show a problem, go straight to our step by step guide on how to fix calcium deficiency in cannabis plants.

What calcium does for cannabis

Calcium has several jobs in the plant. It helps form cell walls, supports the movement of other nutrients and plays a part in overall growth and development. When calcium runs short, problems show up across the plant.

Signs in the leaves

Leaves are usually the first place you notice a shortage. Look for dark spots or dead, brown patches around the leaf edges. Leaf tips may also curl downward, which growers call clawing.

Effects on growth and yield

A lack of calcium affects more than looks. Plants can become stunted and develop weak stems and branches. Weaker plants tend to give smaller yields, and in severe cases the plant can die. Flowers may also come in underdeveloped.

Where cannabis gets calcium

Organic amendments

Organic amendments add calcium naturally. Eggshells, oyster shells and bone meal are rich in calcium and can be blended into your garden soil or compost. They also add other useful nutrients along the way.

Your soil

Some soils, such as chalky soils, naturally hold more calcium than others. Whatever soil you use, check its overall nutrient balance so it meets your plants’ other needs as well. Our guide to the best soil for growing cannabis indoors can help you choose.

Commercial supplements

Calcium supplements for cannabis come in liquid or granular form and fit easily into your regular feeding schedule. Follow the manufacturer’s instructions, since adding too much can throw other nutrients out of balance.

Hydroponic nutrient solutions

If you grow in a hydroponic system, many nutrient solutions already include calcium alongside other essential nutrients. You mix them into your system’s water.

Keeping calcium levels right

Test and adjust pH

Start by testing the pH of your soil or growing medium. If the pH is too high or too low, your plants cannot absorb calcium properly, no matter how much is in the soil. Most cannabis plants prefer a slightly acidic soil pH between 6 and 7.

• pH up or down products. Available at garden supply stores for quick changes.
• Lime. Raises soil pH.
• Sulfur. Lowers soil pH.

For more on reading and adjusting pH, see our guide to understanding pH and how it affects cannabis plants.

Choose how to apply calcium

Foliar sprays put nutrients, including calcium, straight onto the leaves. They can be a quick fix for minor shortages because the plant takes up the nutrients fast. They do not correct the calcium level in the soil, so they cannot replace good soil management.

Soil amendments last longer. Add calcium directly to your soil or growing medium with the organic amendments or supplements above. They raise calcium levels and can also improve soil structure and nutrient balance.

Calcium keeps cannabis strong

Keeping calcium at the right level takes a little extra attention, but it pays off in healthier plants and better yields. Calcium often works alongside magnesium, so it is worth reading our guide on magnesium deficiency in cannabis plants too.