Specs are compiled from manufacturer listings and verified buyer reviews and can change over time — please confirm the key details on the product page before buying.
That black, sunken patch on the bottom of your first ripe tomato is blossom end rot, a calcium deficiency that shows up mid-season. The fix is feeding your plants calcium they can actually absorb, and the right spray or drench stops new fruit from rotting while the good ones ripen.
I’m Rikta — the founder and writer behind Lawn Gear Lab. This guide is built by comparing the manufacturers’ published specifications and the patterns across verified customer reviews, so you get each pick’s real strengths and trade-offs instead of marketing spin.
You want a calcium treatment that prevents blossom end rot on tomatoes, peppers, and squash before it ruins your harvest. The calcium spray for blossom end rot options below are ranked by how quickly they deliver usable calcium to your plants.
Our Picks at a Glance
How To Choose The Best Calcium Spray For Blossom End Rot
Blossom end rot appears when a plant can’t move enough calcium to developing fruit, often because of uneven watering or a soil calcium shortage. A calcium spray puts the nutrient where the plant can use it fast, but only if you pick the right form for how you grow.
Liquid Cal-Mag vs. Calcium Nitrate
Cal-Mag liquids combine calcium with magnesium and often iron, which helps plants that show yellowing leaves alongside rot. Calcium nitrate delivers a strong hit of calcium plus nitrogen, which promotes leafy growth but needs careful dosing so you don’t overfeed nitrogen during fruiting.
Foliar Spray vs. Soil Drench
A foliar spray coats leaves so calcium absorbs directly, which works fast for existing rot but only helps the leaves you cover. A soil drench feeds the roots and supports the whole plant over weeks, making it the stronger choice for preventing rot on new fruit. Many growers use both.
Read the Mixing Ratio
Concentrated products require precise dilution — a 1:1000 ratio means one part product to 1000 parts water. Get this wrong and you risk burning leaves or wasting product. Follow the label exactly, and start with a half dose on seedlings if a product says it is highly concentrated.
Quick Comparison
| Model | Best For | Form | Calcium Source | Volume | Amazon |
|---|---|---|---|---|---|
| General Hydroponics CALiMAGic★ Best Overall | Versatile all-grower Cal-Mag | Liquid | Calcium + Magnesium | 946 ml | Amazon |
| Bloom City Ultra Pure Cal-MagBest Value | Fast rot stopping in soil & hydro | Liquid | Calcium + Magnesium | 32 fl oz | Amazon |
| ENVY CalMag+ (4-0-0)Premium Pick | RO water growers | Liquid | Calcium Nitrate | 32 fl oz | Amazon |
| TPS Cal-Mag Complete | Heavy producers in pots | Liquid | Calcium + Magnesium | 32 fl oz | Amazon |
| Cz Garden Calcium Nitrate 15.5-0-0 | Soil gardens needing nitrogen boost | Granules | Calcium Nitrate | 5 lb | Amazon |
| Bloom City Veggie Cure | Targeted rot treatment for veggies | Liquid | Calcium-rich | 32 fl oz | Amazon |
| GS Plant Foods Cal-Mag Extreme | Micronutrient-hungry plants | Liquid | Calcium + 7 others | 32 fl oz | Amazon |
| TPS Liquid Calcium | Foliar feeding with big coverage | Liquid | Calcium only | 32 fl oz | Amazon |
| ENVY Solution Grade Calcium Nitrate | Long-term soil & hydro supply | Granules | Calcium Nitrate (19% Ca) | 3 lb x 3 | Amazon |
In-Depth Reviews
1. General Hydroponics CALiMAGic Quart
Our pick — over 4.5★ from 9,500+ verified ratings; the strongest balance of quality and price.
The crowd favorite that prevents rot in soil, coco, and hydro alike
CALiMAGic uses a 1-0-0 NPK blend of readily available calcium and magnesium — so no extra nitrogen pushes leafy growth while you are trying to ripen fruit. It dissolves fast with no sediment, and the mixing ratio of 1:1000 means that 946 ml bottle stretches across many feedings.
What wins people over is the consistency: it prevents blossom end rot and tip burn in tomatoes and lettuce, and the quality is praised across hundreds of owner reports. The blend is concentrated, so starting at half the suggested dose is the smart move on seedlings before working up to full strength.
Buyers report it works great, with plants showing instant growth changes and blooms, and one grower used a full crop cycle while still having enough left for two more. A slight pH bump is worth watching in hydro systems, and a few units arrive with leaky caps, so open it over the sink the first time.
Why growers stick with it
- Prevents both blossom end rot and tip burn in one formula
- Won’t clog spray lines or drip emitters
- At 2.8 pounds per bottle, the concentrated value is strong
Watch these details
- Slightly raises pH, so test after mixing
- A few caps leak in transit
Reach for this if: you grow across multiple media — soil, coco, or hydro — and want one reliable Cal-Mag that handles rot wherever it appears.
Look elsewhere if: you need a pure calcium hit with zero nitrogen, since this includes magnesium and a small nutrient blend.
2. Bloom City Professional Grade Ultra Pure Cal-Mag Fertilizer
The rot-stopper with the most buyer praise for actually working
With a 32 fluid ounce bottle and a mixing instruction of just 2-5 ml per gallon of feedwater, this one is built for gardeners who hate complicated dosing. The calcium and magnesium go to work on strong stems and vibrant leaves, and it is suited for indoor houseplants, outdoor gardens, and hydroponic setups alike.
Blossom end rot prevention is the second most-praised aspect here, and effectiveness tops the list — it stopped the rotting of tomatoes caused by insufficient calcium, per buyer reports. One grower saw produce come back to full bloom, and the clean dissolve means no residue buildup or clogging in hydro lines.
At 2 pounds per bottle, compared to the 2.8-pound General Hydroponics CALiMAGic, it is easier to lift and pour during a long feeding session. Beginners find the dosing forgiving, and it works across every skill level without the need for separate measurement tools.
Solid pick if: you want a straightforward Cal-Mag that prevents rot across soil, hydro, and houseplants with one simple dosing rule.
Fair trade-off: the 32 fl oz bottle runs out faster than the concentrated quart from the top pick.
3. ENVY CalMag+ (4-0-0) Professional Grade
The calcium-nitrate based Cal-Mag that beats cloudy blends
ENVY derives its calcium from Calcium Nitrate instead of the Calcium Chloride most blends use, which the maker says is friendlier to plants and hydro systems. The 4-0-0 NPK formula adds magnesium and iron, and it is specifically formulated to replace minerals stripped by reverse osmosis water — a common rot trigger for RO users.
Blossom end rot prevention is a headline feature here, and owners mention that after a couple doses, the rot is gone. It doesn’t cloud up the water like some calmags do, a detail praised by growers who dislike murky reservoirs.
The 32 fluid ounce bottle weighs 1112 g, while the Bloom City bottle weighs 907 g (2 pounds), yet it is still easy to handle. It corrects coir nutrient lock-up, making it a smart addition if you grow in coco and see yellowing leaves despite feeding.
What stands out
- Prevents blossom end rot in tomatoes and peppers
- Replaces minerals stripped by RO water
- Corrects nutrient lock-up in coco coir
Keep in mind
- Performs best when paired with ENVY’s A & B base nutrients
- Fewer total reviews than the top two picks
Best for: RO water and coco coir growers who want a premium calcium source that keeps hydro lines clean.
Think twice if: you are on a strict budget and just need a basic Cal-Mag for soil.
4. TPS Nutrients Cal-Mag Complete
The heavy-hitter for potted growers chasing giant yields
TPS Cal-Mag Complete brings a 1:200 mixing ratio, while the top pick has a 1:1000 ratio, so a 32 fl oz bottle goes a long way for serious gardeners. It supports strong structure and development, and improves nutrient uptake efficiency, which matters when your plants are pushing out heavy fruit loads.
The numbers back it up: one indoor grower harvested 200+ lbs of Red/Pink Brandywine tomatoes with zero blossom end rot and no deficiencies, with plants reaching 10 feet tall and averaging 1 lb tomatoes. Another saw increased calcium and magnesium in harvested greens like broccoli and kale.
At 2 pounds per bottle, it matches the Bloom City weight; the 1:200 ratio versus the 1:1000 top pick means each feeding uses less product. A 4cc per gallon dose lasted months for one grower. Concentration is mixed in owner feedback — a few find it strong, so start low and scale up.
Powerful choice for: potted tomato and pepper growers who want concentrated feeding that prevents crown rot and boosts fruit size.
Note: the higher concentration demands careful measuring; a 5 ml measuring spoon is your friend.
5. Cz Garden Supply Calcium Nitrate 15.5-0-0
The 5-pound granule bag that outlasts every liquid here
When you want maximum calcium per dollar and don’t mind mixing your own solution, this 5 lb bag of greenhouse-grade granules delivers 19% calcium and 15.5% nitrogen. It is 100% water soluble, so it dissolves cleanly without the oily skim that lower-grade agricultural calcium nitrate can leave on roots and equipment.
Bloom rot prevention is the second most-praised aspect, and customers note it eliminated blossom end rot on zucchini and tomato plants after two years of issues. The resealable pouch keeps the rest dry, and the 321 feeding schedule works for hydroponics, drip irrigation, NFT, DWC, soil, coco, Earthbox, and Tower Gardens.
Because a little goes a long way, the 5 lb bag lasts multiple seasons. One apple tree owner saw great improvement after the first dose, and the water-soluble formula supports strong stems and green foliage across vegetables.
Best for: soil gardeners and drip-irrigation users who want a long-lasting, water-soluble calcium nitrate that prevents rot for pennies per feeding.
Consider the catch: the 15.5% nitrogen means it’s not ideal when you’re trying to limit leafy growth during fruiting.
6. Bloom City Veggie Cure
The targeted rot fix that holds up through a wet spring
Veggie Cure is purpose-built for blossom end rot — the 32 fl oz liquid is calcium-enriched and formulated to support tomatoes, peppers, squash, and other fruiting plants. Its 1:10 mixing ratio, while most Cal-Mags have ratios around 1:1000, makes it forgiving for beginners and gentle on stressed plants.
Performance tops the buyer feedback, and end rot reduction is right behind it. One gardener in a very damp spring — historically the worst rot trigger — harvested all perfect tomatoes after using this supplement, and a squash grower with bad rot saw it resolve as long as it was applied regularly.
Made in the USA, this one is best used preventatively through the season. The light ratio means you will go through the bottle faster, but buyers love using it on the whole garden and reordering monthly.
Good if: you want a simple, low-risk liquid to protect tomatoes, peppers, and squash through wet weather.
Fair trade-off: the gentle 1:10 ratio means frequent reapplications compared to concentrated Cal-Mags.
7. GS Plant Foods Cal-Mag Extreme
The eight-nutrient blend that revives stressed plants fast
Cal-Mag Extreme goes beyond the standard two-nutrient mix. Alongside calcium and magnesium, it delivers iron, sulfur, manganese, zinc, boron, and molybdenum — all in a plant-available form with natural chelates for fast absorption. For plants that look tired beyond just rot, this is the richer fix.
Effectiveness leads the praise, and reviewers point out it eliminated blossom end rot while improving root growth noticeably. Orchid growers love it — one saw huge root growth in lava rock after light watering twice weekly. The 2-0-0 NPK means less nitrogen than the Cz Garden option, which is friendlier to fruiting plants.
With a 1 teaspoon per gallon mixing ratio, the 32 fl oz bottle lasts a long time, and one grower noted using just 1/4 tsp per gallon. It mixes easily for irrigation or as a foliar spray and suits soil, container, coco, and hydro setups.
Why it stands out
- Eight nutrients in one bottle for comprehensive correction
- Effective as foliar spray or soil drench
- Low nitrogen 2-0-0 suits fruiting plants
Watch out for
- Too much nitrogen for cannabis plants, per some growers
- Concentration is high — start with a quarter teaspoon
Ideal for: plants showing multiple deficiency signs — rot plus yellowing or slow roots — where a broad micronutrient fix beats a single-element spray.
Skip if: you only need pure calcium and want to avoid extra trace elements.
8. TPS Nutrients Liquid Calcium
The pure-calcium foliar spray with coverage measured in square feet
This one skips magnesium and nitrogen for a pure calcium hit — 32 fluid ounces that covers roughly 1280 square feet when mixed at 2 tsp per gallon of feedwater. It strengthens cell walls and reduces deficiency symptoms, making it a focused tool for rot prevention on tomatoes and other fruiting vegetables.
Shoppers say reversal of blossom end rot on tomatoes in about one week, with thick stems and rapid new growth. One grower in pots saw more Juliettes and Jet Star tomatoes than ever before, and weekly use all summer produced perfect fruit. Root rot reduction is the second most-praised aspect.
Because it works as both a foliar spray and root feed, you can target leaves for fast absorption or drench roots for long-term support. The 2 pound bottle is easy to handle, and the Made in USA formula is ideal if you already run a separate Cal-Mag and just need the calcium boost.
Best if: you want pure calcium with no added nitrogen or magnesium, especially for foliar feeding on a tight weekly schedule.
Note: coverage of 1280 sq ft is the listed max — heavy rot may need the weekly reapplications one buyer used all summer.
9. ENVY Solution Grade Calcium Nitrate (15.5-0-0) 3-Pack
The bulk calcium stash with 9 pounds of rot prevention
Three 3 lb resealable pouches give you 9 pounds of greenhouse-grade calcium nitrate with 19% calcium and 15.5% nitrogen. Each pouch includes a measuring scoop, and the resealable design keeps the granules fresh for use across multiple seasons.
Buyers report it works great for tomato blossom rot and keeps new fruit clean when applied early in the season. One tomato grower in 15 gallon pots sprinkles about 3/4 of a scoop in and around plants every few weeks. It doesn’t fix existing damage but prevents future fruit issues, and visible improvement showed in about 2 weeks.
At 9 pounds total, while other options range from 2 to 5 pounds, this provides the longest supply. The 100% water-soluble formula keeps hydro systems clean with no agricultural preservatives, though solubility gets mixed feedback — one hydro grower dissolves it in warm water first for best results.
Best for: serious gardeners with many plants who want a season-long calcium supply in one purchase.
Think twice if: you only have a few plants — the 9-pound haul may outlast your needs.
Understanding the Specs
NPK Ratio
The three numbers on a fertilizer label stand for nitrogen, phosphorus, and potassium. A 1-0-0 Cal-Mag has almost no nitrogen, which is good for fruiting plants, while a 15.5-0-0 calcium nitrate carries significant nitrogen that boosts leafy growth — useful early, but watch it during flowering.
Mixing Ratio
This tells you how much product to dilute per gallon of water. A 1:1000 ratio means 1 part product to 1000 parts water — about 4 ml per gallon — while a 1:10 ratio needs much more product per feeding. Concentrated products last longer but demand careful measuring.
FAQ
How fast does calcium spray fix blossom end rot?
Should I spray the leaves or water the roots?
What is the difference between Cal-Mag and calcium nitrate?
Why does blossom end rot keep coming back even after spraying?
Can I use calcium spray on peppers, squash, and zucchini too?
How much calcium spray should I use per gallon of water?
Will calcium spray work in hydroponic systems?
Does nitrogen in calcium nitrate harm fruiting plants?
Final Thoughts: The Verdict
For most gardeners, the winning calcium spray for blossom end rot is the General Hydroponics CALiMAGic because it prevents rot across soil, coco, and hydro with a 1-0-0 NPK that won’t push unwanted leafy growth. If you want the fastest rot reversal with the most buyer confidence behind it, the Bloom City Ultra Pure Cal-Mag is the one to reach for. And for the biggest bang over multiple seasons, the Cz Garden 5 lb calcium nitrate delivers pure calcium at the lowest cost per feeding.
How We Picked
We do not accept paid placement. Every pick is matched to a real buyer and a real use-case; we do not hands-on test units.
Sources & Methodology
Specifications: manufacturer listings and product documentation. Review insights: verified customer reviews, as of August 2026. Pricing: not shown on this page (it changes often); check the current price via the retailer link.
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