About CalMag for Plants: Calcium and Magnesium Supplements
CalMag tops up calcium and magnesium, the two nutrients that tend to run short first when you feed with soft tap water or RO water, or grow in coco. Calcium helps build strong cell walls and roots, while magnesium sits at the heart of chlorophyll, so plants can turn light into energy.
Every CalMag here is an additive that works alongside your base feed rather than replacing it. Add it to tomatoes, chillies, peppers, herbs, salad, strawberries and houseplants to keep leaves green and new growth strong from seedling to harvest.
We stock CalMag from Canna, BioBizz, Shogun, Athena, Plant Magic, Monkey, Mills, Dutch Pro, Plagron and Ionic, plus single element Canna Mono bottles for fine tuning. Free UK delivery on orders of £94.99 or more (large 19L to 25L containers have a delivery charge shown at checkout), we price match, and Click & Collect is available from our West Bromwich store.
How to choose a CalMag
Start with your water and your growing medium. If your tap water is soft, you use RO water or you grow in coco, a CalMag top up is the usual answer. Plant Magic notes that coco can bind calcium and magnesium, and that LED lighting can raise demand. On hard water you may not need one at all.
| Product | What stands out | Dose on our product page |
|---|---|---|
| Shogun CalMag | Liquid calcium and magnesium for soil, coco and hydro, sizes from 250ml to 25L | 1 to 3 ml per litre |
| Canna CalMag Agent | Made for soft tap water or RO water, in 1L, 5L or 10L | Follow the label |
| BioBizz CalMag | 100% organic and certified, fits any BioBizz feeding schedule | Follow the label |
| Plant Magic MagneCal+ | Aimed at soft water, coco and LED grow rooms | 0.5 to 1 ml per litre |
| Athena Cal Mag | Clean soluble formula for RO water and inert media such as coco and rockwool | 2.5 ml per US gallon, or Athena's feed schedule |
| Dutch Pro Cal Mag | Concentrated, includes a small amount of nitrogen, free from PGRs | 0.1 to 1 ml per litre |
| Monkey Mag Cal and Mills CalMag | Partner the Monkey and Mills base feeds, suit soil, coco and hydro | 1 to 3 ml per litre |
| Ionic Tonic | Calcium in three forms including chelated, plus chelated iron, amino acids and seaweed extracts | Follow the label |
| Canna Calcium Mono and Canna Magnesium Mono | Single element bottles to correct one shortage without adding the other | Around 1 to 2 ml per litre |
Already running a full feed range? Matching the brand keeps things simple: Canna CalMag Agent with Canna, BioBizz CalMag with BioBizz, Shogun CalMag with Shogun and so on. Our guide to reading a nutrient feed chart shows where CalMag fits in a weekly schedule.
CalMag FAQs
Do I need CalMag with hard water?
Often not. Hard water already carries calcium and magnesium, so many growers on hard water skip it. It earns its place with soft tap water, RO water, coco, or when plants show signs of shortage.
What are the signs of a calcium or magnesium shortage?
Canna lists rusty spots and weak new growth for calcium, and yellowing between the veins on older leaves for magnesium. Shogun adds leaf curl and blossom end rot, a problem tomato and pepper growers know well. Bring a leaf into the store and we will take a look.
When do I add CalMag to my feed?
Canna, Athena and Dutch Pro all say to add CalMag to clean water first, then your base nutrients and any other additives. Check and adjust pH once everything is mixed.
Can I use CalMag in soil, coco and hydro?
Yes. The CalMag products in this range are made for soil, coco and hydroponic systems. Coco growers tend to use it most, as coco can hold on to calcium and magnesium.
Does CalMag replace my base nutrients?
No. CalMag is a supplement that sits alongside a complete base feed. Browse our base nutrients and the wider additives and boosters range to build the rest of your feeding programme.
Need advice? Visit our West Bromwich store, call 0121 553 7872 or WhatsApp our experts.