Cal-Mag Fertilizer
Give heavy-feeding plants convenient calcium and magnesium support in one liquid supplement. Cal-Mag Fertilizer is made to fit alongside a complete feeding program when plants need extra support from these two nutrients.
Mix it into your regular feedwater as directed for consistent cal-mag support without complicating the routine.
Made by growers
More than a bottle on a shelf.
- Talk to real plant people. The team that mixes the formula answers your email.
- Made in-house, in the USA. Every bottle mixed and filled by us, not a third party.
- We're growers, not resellers. We use this on our own plants before it ships.
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Cal-Mag Fertilizer with 2% calcium and 0.6% magnesium plus iron and a full micro package — a cal-mag supplement made to correct the two most common secondary-nutrient shortfalls in one bottle. Calcium builds strong cell walls and magnesium sits at the center of chlorophyll, so together they head off the blossom-end rot and interveinal yellowing that show up when plants, especially in containers and coco coir, run short.
How to Use Cal-Mag Fertilizer
| Method | Amount | How Often |
|---|---|---|
| Watering can | 1/2 to 1 tsp per gallon of water | Spring & Summer: apply every watering |
| Watering can | Same dilution | Fall & Winter: every 2-4 weeks |
| Hose-end sprayer | Set to 1 tsp setting | Spring & Summer: apply every watering |
| Leaf misting (optional) | 1 tsp per quart (32 oz) of water, spray on leaves | apply weekly |
Use alongside your regular fertilizer, not in place of it — this supplies calcium, magnesium, and micros, not a full N-P-K feed. It's mild enough to use at every watering during the growing season.
What's Inside
This is a cal-mag supplement rather than a complete fertilizer — it carries a small 2% nitrogen (all nitrate) but no phosphorus or potassium, because its job is the two secondary nutrients plants most often run short on. The 2% calcium builds cell walls and holds new tissue together, so a shortfall shows in the newest growth: distorted growing tips and the blossom-end rot that sinks in on the bottom of tomatoes, peppers, and squash. The 0.6% magnesium sits at the center of the chlorophyll molecule, so a magnesium shortfall shows as yellowing between the veins on older leaves.
Beyond calcium and magnesium: a full micronutrient package of boron, copper, iron, manganese, and zinc rounds out the blend, since these traces work alongside cal-mag in healthy growth — boron in particular pairs with calcium in cell-wall structure. This combination is especially valuable for plants grown in containers, coco coir, or under heavy feeding, where cal-mag is depleted fastest. One honest note: blossom-end rot is often an uptake problem driven by uneven watering, so steady soil moisture matters as much as the calcium itself.
Made For
Built as a cal-mag supplement for calcium- and magnesium-hungry plants and growing media — tomatoes, peppers, and squash prone to blossom-end rot, plus any plants in containers, coco coir, or hydroponic and heavy-feeding setups where cal-mag runs short.
Problems It Solves
- Blossom-end rot on tomatoes, peppers, and squash
- Yellowing between the veins on older leaves
- Distorted or dying new growing tips
- Cal-mag deficiency in coco coir or container growing
FAQs
How often should I use cal-mag fertilizer?
In spring and summer, it's mild enough to use at every watering at 1/2 to 1 tsp per gallon; in fall and winter, cut back to every 2-4 weeks. Use it alongside your regular fertilizer, since it supplies calcium, magnesium, and micros rather than a full N-P-K feed. For plants in coco coir or containers, or heavy feeders prone to cal-mag shortfalls, the every-watering routine keeps a steady supply of both nutrients available.
What is cal-mag used for?
It corrects the two secondary-nutrient deficiencies that show up most often together: calcium and magnesium. Calcium prevents blossom-end rot and supports strong new growth, while magnesium keeps leaves green by supporting chlorophyll. It's especially popular for plants grown in coco coir and containers, which are naturally low in both, and for heavy feeders under strong light. Think of it as filling the cal-mag gap that many complete fertilizers leave, used alongside your main feed.
Will cal-mag fix blossom-end rot?
It helps, but it's often not the whole answer. Blossom-end rot usually comes from inconsistent watering that stops the plant from moving calcium into the fruit, even when calcium is present in the soil. So steady, deep watering plus mulch is the first and most important fix. Cal-mag helps when the soil or medium is genuinely short on calcium — common in coco coir and containers — but if watering swings between dry and soaked, supplementing alone frequently won't stop the rot.
Do I need cal-mag if I grow in coco coir?
Usually yes. Coco coir naturally holds onto calcium and magnesium and can even lock them away from the plant, so cal-mag deficiency is common in coco even when you're feeding regularly. Many coco growers add cal-mag as a standard part of every feeding, which is why this product is mild enough to use at every watering. If you grow in coco or a similar inert medium, adding cal-mag from the start usually prevents problems before they show.
When will I see results?
New growth and fruit that develop after you start will benefit, but existing blossom-end rot, damaged tips, or yellowed leaves won't reverse — those are already affected. With consistent use plus even watering, later growth and fruit come in healthier over the following weeks. Because deficiencies build up over time, using cal-mag steadily through the season prevents problems better than reacting once symptoms appear.