Cal-Mag Deficiencies in Cannabis: Quick Fixes and Prevention
Cannabis plants require a balanced amount of essential nutrients for an abundant harvest. This means that when you have an excess of one or a deficiency of another, you can throw the entire balance off. Imbalance in cannabis cultivation can reduce yield, potency, and overall plant health. That’s why it is so important to understand how various cannabis deficiencies can arise. To explore the deficiencies, check out our full exploration of cannabis deficiencies.
One of the most common deficiencies growers encounter is Cal-Mag, and as a result, many issues in the garden are treated with more Cal-Mag, often unnecessarily.
This guide delves into fast fixes for these deficiencies, signs to look out for, and long-term solutions to ensure your cannabis plants remain healthy and productive. Let’s explore nutrient deficiencies and toxicities in your garden today.
How to Fix Calcium and Magnesium Deficiencies in Cannabis
The first thing to figure out is whether you have a true Cal-Mag deficiency. Calcium and magnesium need to be applied in a specific proportion to one another, typically ranging from 2:1 to 5:1 calcium to magnesium. It is important to balance these nutrients because they are cations, meaning they take up cation exchange space on your plant’s roots.
Sometimes symptoms of a deficiency are caused by an abundance of other cations, particularly potassium, that may take up too many of the cation exchange receptors. A simple N-P-K test can tell you if your potassium is too high, and performing tests every 2-3 months can show you how your plants are consuming macro nutrients. An in-depth soil analysis can give you a complete picture of your soil’s nutrient composition.
pH Problems
Incorrect pH in your medium can hinder nutrient uptake. The ideal soil pH range is 6.0-7.0. Below 6.0, nutrient competition occurs, while above 7.5, magnesium becomes less available. Use elemental sulfur to lower pH or lime to adjust soil pH. Similarly, nutrient solution pH affects calcium and magnesium uptake. If too low (below 5.5), these nutrients may leach or become unavailable, and if too high (above 6.5-7.0), they can precipitate as insoluble compounds, leading to deficiencies and plant health issues like chlorosis, weak stems, and poor roots.
Quick Fixes
If you’re truly facing calcium and magnesium deficiencies in your cannabis plants, don’t worry, there are quick fixes available. Here are a few easy solutions to correct the problem:
- Cal-Mag Supplements: These products combine calcium and magnesium, allowing for easy absorption. They are available in most grow shops and can be used as a soil drench or foliar spray. Check product labels for proper dosages and apply every few days until the symptoms disappear.
- Epsom Salt Solution: For magnesium deficiency, dissolve one teaspoon of Epsom salt in one gallon of water and apply as a foliar spray. Epsom salt provides magnesium quickly, and foliar application delivers nutrients directly to the leaves for a fast response.
- Water-Soluble Calcium: This home remedy can help supplement calcium. Crush cooked eggshells into a fine powder or mix oyster shell flour with vinegar. Allow to sit for seven to ten days, strain and dilute, and apply to the root zone. This method is slower than store-bought nutrient supplements but provides an organic solution to help replenish calcium over time.
Calcium’s Role in Cannabis Cultivation
Calcium strengthens cell walls and ensures plants can withstand environmental stress. This nutrient supports root development, nutrient transport, and overall plant structure. Calcium also helps prevent diseases and supports proper enzyme function, making it an essential element throughout all stages of growth.
Magnesium’s Role in Cannabis Cultivation
Magnesium is equally important as it is a central atom in chlorophyll, enabling plants to photosynthesize. Without sufficient magnesium, cannabis plants can’t effectively produce energy, leading to stunted growth and poor bud production. This nutrient also plays a role in enzyme function and the metabolism of carbohydrates, which helps fuel growth and flowering.
To learn more about specific nutrients for autoflowers, see our guide on the 5 Nutrients for Autoflowers.
Signs of Calcium and Magnesium Deficiency
Identifying calcium and magnesium deficiencies early can save your crop from serious damage. Here are some visual signs to help you diagnose both magnesium and calcium deficiency in weed.
Calcium Deficiency in Cannabis Signs:
- Brown Spots: Small brown spots appear on newer leaves, usually starting at the edges.
- Poor Root Development: Calcium is essential for root growth, so stunted root systems or weak stems may indicate a deficiency.
- Curled Leaves: Young leaves may curl or twist due to cannabis calcium deficiency and the impact on cell structure.
Symptoms of Magnesium Deficiency in Weed:
- Yellowing Between Veins: In cannabis, Magnesium deficiency often causes interveinal chlorosis, which leaves yellow between the veins.
- Purple Stems: Purple stems or dark veins in cannabis can indicate magnesium deficiency, though this can vary by strain.
- Leaf Necrosis: Advanced magnesium deficiency may cause the edges of older leaves to become crispy or exhibit leaf necrosis (leaf death).
Key Factors for Long-term Prevention
If calcium and magnesium deficiencies are recurring, adjusting your cannabis nutrient strategy and watering practices can promote healthier plant growth. Start by using high-quality nutrients from reputable brands with organic options for sustainability.
Proper watering cycles are crucial in growing cannabis. Avoid overwatering, which can cause nutrient leaching, as both calcium and magnesium are mobile nutrients in water. Keep the medium moist but not overly saturated. Conversely, insufficient watering can lead to calcium deficiencies since calcium moves through water within the plant and becomes immobile once it reaches the cell walls. Magnesium, however, is highly mobile within the plant and can redistribute itself as needed.
Your water source also matters. Tap water, reverse osmosis (RO), and well water vary in calcium and magnesium content. Well water may contain these nutrients, while RO water lacks them entirely. Test your water to understand its impact on nutrient availability.
For long-term solutions, soil growers with a pH of 6.0 or below can amend with dolomite lime, which slowly releases calcium and magnesium while raising pH. Basalt rock dust is another slow-release option that’s better for soils with a pH of 6.0 or higher, as it has less influence on pH.
For immediate results, use soluble or chelated forms of calcium and magnesium. These are less affected by pH fluctuations and are ideal for hydroponics. They can also serve as a weekly supplement for soil grows.
Photos courtesy of Kandid Kush
About the Author: Alexandria Irons
