Shogun CalMag | Calcium & Magnesium Plant Feed for Coco & Soft Water

Shogun CalMag – Calcium & Magnesium Supplement for Coco, Soft Water & Houseplants - image 8

Shogun CalMag – Calcium & Magnesium Plant Nutrient for Coco, Hydro & Houseplants

£12.95

Size 250ml 1 Litre 5 Litres 10 Litres 25 Litres Syringe Only

⚙️ Type: Mineral
Refined minerals your plant can use straight away: fast-acting and precise. The tradeoff: it's possible to overdo mineral feeds, so stick to the dose and check your EC.

The plant feed nobody budgets for, and every grower ends up needing

There is a curious hierarchy in plant feeding. Nitrogen gets top billing. Phosphorus and potassium get flashy "bloom booster" bottles with pictures of enormous tomatoes on them. Calcium and magnesium get nothing at all, which is odd, because they're the two elements most likely to run out first.

And when they run out, nothing dramatic happens. There's no collapse, no crisis. Just rusty brown spots, yellowing between the leaf veins, weak new growth and a plant that is somehow underperforming without anyone being able to say why. It's the horticultural equivalent of a slow puncture.

SHOGUN CalMag is the fix that costs pennies a watering. It's a refined, plant-available blend of calcium, magnesium, nitrogen and chelated iron, designed by Shogun to do more than plug a gap. Calcium and magnesium are the delivery drivers of the plant world, helping move other nutrients to where they're needed. Keep them topped up and everything else in your feed works harder.

Who needs CalMag? More people than think they do

Coco coir growers: Coco naturally holds on to calcium and magnesium, stealing them from your feed. CalMag is close to essential in coco, especially through vegetative growth.
Soft water areas: Much of Scotland, Wales, the North and the South West has soft tap water with very little calcium or magnesium in it.
RO, filtered and rainwater users: The purer the water, the emptier it is. Great for fussy plants, but it leaves them short of minerals.
LED growers: Plants under LEDs transpire less, so they draw up less calcium. A little CalMag closes the gap.
Houseplant collectors: Watering Calathea, Maranta, ferns or Alocasia with rainwater or a filter jug? Add a splash of CalMag and they get the minerals their water no longer provides.
Heatwaves and growth spurts: Fast-growing plants in hot weather burn through calcium quickly, which is when shortages usually show.

Signs your plants are running short

Low magnesium: Yellowing between the veins of older, lower leaves while the veins stay green.
Low calcium: Rusty brown spots, crinkled or twisted new leaves and weak stems.
Low iron: Pale, yellow new growth at the top of the plant.

A few millilitres in every watering keeps plants topped up, so these signs never appear.

Key Features

Calcium, magnesium and nitrogen: Builds strong cell walls, keeps leaves deep green and supports chlorophyll production.
Chelated iron: A micronutrient that often runs short, in a form plants can absorb easily.
Improves nutrient uptake: Helps your plants move and use the rest of their feed more efficiently.
Root feed or foliar spray: Feed it at the roots for a steady supply, or spray it on the leaves for a quick top-up.
All media: Suitable for soil, coco and hydroponics, alongside any base nutrient.

How to Use

Root feed: Add 1–2ml per litre to your watering can or reservoir. Use throughout vegetative and flowering growth.
Foliar spray: When leaves show signs of running short, mix 15ml per litre, adjust the pH to between 5 and 7, and spray onto the leaves once a week until the problem clears. Spray with the lights off or out of direct sun.
Houseplants: Start at the low end, around 1ml per litre in your watering can.

Feeding Schedule

Shogun's official 2026 LED Coco & Terra feed chart recommends CalMag as a root treatment at 0.5–1ml per litre when you are watering with pure, distilled, RO or soft water. In moderately hard water (around EC 0.4) no extra CalMag is needed. With Samurai Terra Light Mix soils, Shogun advise always adding CalMag at 0.5–1ml per litre.

🌱 Rose's Pro-Tip: Add CalMag to your water first and stir before anything else goes in. Concentrated calcium mixed straight into phosphorus-rich feeds can react and drop out of solution, and then neither does its job. Water first, CalMag second, base feed third, extras last. And remember CalMag contains nitrogen and raises your EC, so check your EC after mixing and adjust your base feed if needed.

Which Size?

250ml: A houseplant collection or a single small grow. Treats up to 250 litres of water at 1ml/L.
1 Litre: The everyday grower's bottle.
5 Litres: Better value for regular coco and hydro growers.
10 Litres: Multi-tent and larger setups.
25 Litres: The lowest cost per litre for big grows.
Syringe Only: For measuring small doses accurately, rather than guessing.