Tomato feed and Cal-Mag for fruit that marks at the blossom end
Tomato feed and Cal-Mag is the pair for a mid-summer problem: the blend is feeding the crop, but fruit still marks at the blossom end.
The tomato blend feeds the crop steadily through the season. The Cal-Mag covers calcium and magnesium when erratic watering stops calcium reaching the fruit. Together they deal with both halves of what most growers meet in July: feeding looks right, fruit still browns at the blossom end. What is in the pair: Organic Tomato Fertiliser: 1.5 kg (two 750 g bags); Cal-Mag for Plants: 750 g. Entry-size packs. Each product keeps the application rate on its own listing; we have not set a combined rate. Blossom end rot on tomatoes is usually water as much as calcium. Cal-Mag keeps supply up; it does not replace a steady can. Read Calcium for Tomatoes and the Cal-Mag listing before treating this as a cure. More in Tomatoes & Edibles and Bundles & Kits.
Pick a size on the product form. Each size is a full set of the named packs below, not a single bag.
- Entry (1.5 kg tomato + 750 g Cal-Mag): Organic Tomato Fertiliser 3-4-6: 1.5 kg (2 × 750 g); Cal-Mag for Plants: 750 g
- Mid (4 kg tomato + 1.5 kg Cal-Mag): Organic Tomato Fertiliser 3-4-6: 4 kg; Cal-Mag for Plants: 1.5 kg
- Large (9 kg tomato + 3 kg Cal-Mag): Organic Tomato Fertiliser 3-4-6: 9 kg; Cal-Mag for Plants: 3 kg
Rates stay on each component listing. The size picker only changes how much of each pack you get.
Both are also sold on their own: Tomato Fertiliser · Cal-Mag for Plants
When this pair is the right buy
- Tomato feed and Cal-Mag in growbags and pots, where peat-free mixes hold little of their own
- Fruit that marks at the blossom end while the plant otherwise looks fed
- Greenhouse tomatoes on rainwater, which carries almost no calcium
- Growers who already buy tomato feed and Cal-Mag in the same week
Feed plus calcium and magnesium
- Tomato plant feed for the season; Cal-Mag as the calcium and magnesium top-up
- Honest about watering: calcium has to reach the fruit
- Each product keeps its own rate
Tomato feed on its own
- Enough if fruit is clean and water is steady
- The Tomato & Vegetable pair is tomatoes plus the plot, not tomatoes plus calcium
Dr Forest packs this in Stockport. Cal-Mag is mined gypsum and kieserite with a trace of boron. Made with organic ingredients; we do not call it certified organic.
Calcium for tomatoes, and why watering still decides it
Blossom end rot tomatoes is a calcium failure at the fruit, not always a calcium failure in the bag. Calcium is immobile in the phloem; it travels with the transpiration stream. Uneven watering, a dry spell then a soak, or a wildly fluctuating greenhouse, will mark fruit even when the soil analysis looks fine.
Cal-Mag for plants here is gypsum and kieserite, pH-neutral, with a trace of boron because boron and calcium work together in cell walls (Brown et al., 2002). It is a soil product, not a foliar spray, and not a human supplement.
This page does not invent a combined rate and does not claim to cure blossom end rot. The mechanism is supply plus steady water.
Tomato feed for bulk nutrition
3-4-6 through the season, rate on the tomato bag.
Calcium and magnesium on the side
Cal-Mag is the structural-cation bag, not another NPK.
Boron as a trace partner
Present in Cal-Mag at a small, labelled inclusion; do not stack a second boron product.
Watering is not optional
Erratic watering is still the usual cause of marked fruit.
References
- Marschner, P. ed. (2012). Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press.
- Brown, P.H. et al. (2002). Boron in plant biology. Plant Biology, 4(2).
- Shainberg, I. et al. (1989). Use of gypsum on soils: a review. Advances in Soil Science, 9.
- Kopittke, P.M. & Menzies, N.W. (2007). The basic cation saturation ratio and the 'ideal' soil. SSSA Journal, 71(2).
- Canellas, L.P. et al. (2015). Humic and fulvic acids as biostimulants in horticulture. Scientia Horticulturae, 196.
- Wang, Y. et al. (2023). Combined organic–mineral fertilisation meta-analysis, 7,859 data pairs. Science of the Total Environment.
How to use Tomato Feed & Cal-Mag Pair
Use the tomato listing for the feed. Use the Cal-Mag listing for calcium and magnesium. Cal-Mag is typically added at a tenth of the feed weight on that page; follow that page, not a pair average.
Keep watering even. Do not treat marked fruit as something a stronger dose will reverse; calcium fixes new growth, not the fruit already damaged.
Tomato feed
Cal-Mag
Cal-Mag for Plants. Usually 10% of the feed weight on that listing. Do not invent a pair handful.
- Apply tomato feed as the tomato page describes.
- Add Cal-Mag as the Cal-Mag page describes, to the root zone, not through a sprayer.
- Water steadily. A dry-then-flood cycle will still mark fruit.
- Background: Calcium for Tomatoes.
Need vegetables as well as tomatoes? Tomato & Vegetable Feed Pair. Liquid calcium on clay is a different job: Liquid Gypsum.
Tomato Feed & Cal-Mag Pair: questions
It supplies calcium and magnesium and the tomato feed. Watering still has to be steady. Already-marked fruit will not un-brown.
Gypsum and kieserite with a trace of boron and fulvic acid. Full detail on Cal-Mag. It is not a human supplement.
No. Follow each listing. Cal-Mag has its own 10% rule on that page.
The tomato blend is a soil feed. Cal-Mag is a soil product and will clog a sprayer. Root zone only.
Made with organic ingredients. We do not call it certified organic.
Stockport.
1.5 kg tomato blend (two 750 g bags) and 750 g Cal-Mag.
Yes. At today's prices (October 2026) every size costs about 10% less than buying the same products separately. The smallest size is £19.79 against £21.99 bought one by one, a saving of £2.20. Check each product page for current single prices.
Not in the bundle. The sizes are fixed: 1.5 kg tomato + 750 g Cal-Mag; 4 kg tomato + 1.5 kg Cal-Mag; 9 kg tomato + 3 kg Cal-Mag. If you want different amounts, buy the products on their own pages and mix the sizes as you like.
Yes. Each one is sold on its own: Tomato Feed 3-4-6, Cal-Mag for Plants.