Calcium Fertilizer: Roles, Sources and How to Prevent Deficiency

A calcium fertilizer supplies the calcium that holds plant cell walls and membranes together, but whether it reaches the fruit depends as much on water flow as on the fertilizer you choose. Calcium travels with water to the leaves and barely moves out of them again, so fruit and young leaves can run short even on calcium-rich soil (Hawkesford et al., 2023). This guide explains what calcium does, why deficiency disorders happen, which calcium fertilizer fits which goal, and when soil, fertigation or foliar calcium makes sense.

What calcium does in plants

Most calcium in plant tissue sits in the cell walls, bound to pectins in the middle lamella. When calcium supply is low, 70% to 99% of the calcium in the leaves of broadleaf crops can be in the cell walls (Hawkesford et al., 2023). Calcium pectate strengthens the walls and blocks the enzyme that breaks pectins down, so a typical sign of shortage is the collapse of tissue in petioles, stem tips and fruit (Hawkesford et al., 2023). In citrus, calcium applied during early fruit growth increased the calcium bound to pectin in the peel, kept the peel firmer and reduced fruit cracking by 71% (Dong et al., 2025).

Calcium also stabilizes cell membranes, which limits leakage of sugars and other solutes under stress such as chilling or waterlogging, and it acts as a signal inside the cell that triggers responses to drought, salinity, cold and pathogen attack (Hawkesford et al., 2023). Plants can hold a lot of it: plant calcium ranges from about 1 to 50 mg per gram of dry matter, and mature leaves can exceed 10% calcium without harm (Hawkesford et al., 2023).

Needs differ by crop. In nutrient-solution trials, tomato needed 12.9 mg calcium per gram of dry matter for full growth, against 0.7 mg for perennial ryegrass, because broadleaf crops have more calcium-binding sites in their cell walls than grasses (Hawkesford et al., 2023).

Why crops run short of calcium on calcium-rich soil

Calcium moves from the roots in the xylem, the water-conducting tissue, so it goes where the water goes: to the leaves that transpire most. Its mobility in the phloem, which feeds fruit, tubers and enclosed young leaves, is extremely low (Hawkesford et al., 2023). Leaves draw most of the xylem sap and usually hold far more calcium than fruit (de Freitas & Mitcham, 2012). Adding more calcium to the soil raises calcium in transpiring leaves, but not necessarily in low-transpiring organs such as fleshy fruit, tubers and enclosed leaves (Hawkesford et al., 2023).

That is why deficiency disorders are usually local, in one organ, rather than a shortage across the whole plant. Four conditions make them more likely (Kutman, 2023):

• Competing cations: high ammonium, potassium or magnesium.
• Fast growth: strong light and high nitrogen dilute calcium in the growing tissue.
• Low transpiration: cool temperatures, high humidity and still air, common in greenhouses.
• Stress: drought and salinity.

Fruit total calcium is a poor guide on its own. Fruit with symptoms can hold as much calcium as sound fruit, no threshold concentration has been set, and ratios such as K:Ca, Mg:Ca and N:Ca predict risk better (de Freitas & Mitcham, 2012). Read leaf and fruit analyses together with potassium and magnesium; for potassium’s role see our guide to potassium fertilizers.

Calcium deficiency disorders by crop

Sources: Kutman (2023) and Hawkesford et al. (2023), in Marschner’s Mineral Nutrition of Plants; Robinson & Galán Saúco (2010) for banana.

Signs of calcium deficiency show first on young, fast-growing tissue and on fruit, not on old leaves, because calcium is not moved out of older leaves (Hawkesford et al., 2023). Look for tipburn on expanding leaves, as in lettuce, collapsed tissue at stem tips and leaf stalks, and sunken or dark patches on fruit, such as blossom-end rot in tomato and bitter pit in apple (Hawkesford et al., 2023; Kutman, 2023).

Blossom-end rot is the most common fruit disorder linked to local calcium deficiency (Kutman, 2023). For banana, see Calcium deficiency in banana.

Types of calcium fertilizer

The right calcium fertilizer depends on the job: correcting soil acidity, adding calcium without changing pH, feeding calcium in season through drip, or reaching fruit directly with a spray.

Sources: University of Maryland Extension, Table B-6 (Ca content); Mittenthal et al. (lime and gypsum); Robinson & Galán Saúco (2010), Table 9.3 (solubility); Agriculture Victoria (2023) (calcium nitrate on acid soils); Fernández et al. (2013) (foliar carriers); Waheed et al. (2019), Seesanong et al. (2023) and Thongkam et al. (2021) (shell composition, 94–99% CaCO₃; Ca = CaCO₃ × 0.40, our calculation); Sebonela et al. (2024) and Vu et al. (2022) (eggshell as liming material). Product labels give calcium as CaO: CaO × 0.715 = Ca.

Lime and gypsum

Lime and gypsum both add calcium, but only lime changes soil pH. In lime it is the carbonate, not the calcium, that neutralizes acidity and raises pH; gypsum has no carbonate, so it adds calcium and sulfur without raising pH (Mittenthal et al., n.d.). Use lime where the soil is acid, and gypsum where you need calcium but the pH is already where you want it.

Calcium nitrate fertilizer

Calcium nitrate is the main soluble calcium fertilizer for fertigation. It carries 19.4% calcium (University of Maryland Extension, n.d.) and dissolves at about 102 kg per 100 L of water at 20 °C (Robinson & Galán Saúco, 2010). Its nitrate nitrogen has an alkaline reaction, so on acid soils calcium nitrate can make up a significant part of the nitrogen supply (Agriculture Victoria, 2023). Calcium nitrate is incompatible with phosphate and sulfate solutions (UC Agriculture and Natural Resources, n.d.), so it goes in its own stock tank.

Liquid calcium fertilizer and calcium-boron products

Liquid calcium fertilizers are used mainly for foliar and fruit sprays. Common carriers include calcium chloride and calcium acetate; calcium chloride also acts as a humectant that keeps the spray film wet for longer, which can help uptake in dry climates (Fernández et al., 2013). In bagged apple, sprays of calcium chloride, calcium nitrate and calcium formate all reduced bitter pit; two early sprays (5 and 40 days after full bloom) cut it by 68% to 73%, against 43% to 54% for two later sprays (Yu et al., 2018). Calcium-boron products combine two nutrients that work together in the cell wall, covered below.

Soil, fertigation or foliar calcium?

Match the route to the problem:

• Soil: lime or gypsum before planting builds the soil’s calcium supply and, with lime, corrects pH. This is the base of any program.
• Fertigation: calcium nitrate or calcium magnesium nitrate through drip keeps calcium in the root zone during the season, alongside water.
• Foliar: a calcium foliar spray only helps the tissue it wets, because calcium does not move from leaves to fruit in the phloem (Hawkesford et al., 2023).

A calcium foliar spray works best when it reaches the fruit directly and is repeated. Preharvest calcium sprays reduced bitter pit and improved firmness and storage life in apple, and reduced storage problems in peach, pear and grape (Yamane, 2014). Spraying several times with calcium salts during fruit development raises fruit firmness and delays ripening (Hawkesford et al., 2023). In apple, the fruit surface takes up calcium most readily early in fruit development, while stomata and fine hairs are still present (Fernández et al., 2013), so start early. In a four-season apple trial, calcium chloride sprays reduced bitter pit more than calcium applied to the soil, and adding soil calcium to the sprays gave no extra benefit (Torres et al., 2017). In pomegranate, two calcium sprays reduced fruit cracking and raised marketable yield, though total yield did not change (Davarpanah et al., 2018). In blueberry, high nitrogen rates made green fruit drop worse, and frequent calcium sprays from mid-bloom reduced it, often to negligible levels (Gerbrandt et al., 2019).

Results differ by crop. For blossom-end rot in tomato, extension specialists rate calcium sprays as ineffective and put even soil moisture first, for example with drip irrigation and mulch (Ballew, 2020). Managing humidity, temperature and drought or salinity stress is part of preventing calcium disorders alongside fertilization (Kutman, 2023).

Calcium with biostimulants

Biostimulants are not calcium sources, and trials so far do not show them raising calcium uptake, but some can add to what calcium does. In a pot trial with tomato irrigated with saline water, gypsum in the substrate cut blossom-end rot in the first truss from 31% to 15%, and adding a protein hydrolysate through the drip cut it to 0%. Yet the hydrolysate did not significantly raise calcium in the fruit or leaves; the authors linked the extra effect to amino acids such as proline in the fruit (Franco et al., 1994). In pepper, calcium nitrate sprays cut blossom-end rot from 12% to 4%; adding a seaweed extract raised yield further, from 39 to 45 t/ha, but did not reduce the rot further (Constantin et al., 2024). In sweet cherry, calcium alone made fruit firmer and slowed ripening, while seaweed alone increased fruit size and color (Santos et al., 2025). Use the calcium fertilizer for calcium, and treat a biostimulant as a separate input for growth and stress tolerance. For how biostimulants work, see Biostimulants for crops.

Calcium boron fertilizer: why the two go together

Boron stabilizes the pectin network of the cell wall, and the borate complex it forms in the wall is far more stable when calcium is present (Brown et al., 2002). Like calcium, boron is required for cell wall integrity and is immobile in the phloem of most plants (Kutman, 2023). That makes a calcium boron foliar fertilizer a logical choice for flowering and early fruit development, when new cell walls are forming. Boron is also toxic in excess (Brown et al., 2002), so follow the label rate.

Calcium and plant health

The share of calcium pectate in cell walls affects how easily tissues are broken down by fungi and bacteria (Hawkesford et al., 2023). In a pot trial with Cavendish banana plantlets, adding calcium carbonate, calcium hydroxide or calcium sulfate to the soil reduced germination of Fusarium wilt spores and disease severity by one-third to one-half, at rates too small to change soil pH (Peng et al., 1999). The authors note that the effect still has to be shown in the field. Calcium is part of balanced nutrition that supports healthy tissue; it is not a disease control.

Van Polder calcium products

• LS CalciBo Liquid (16% CaO, 8.2% nitrate N, 0.2% B): a calcium boron foliar fertilizer for flowering and fruit development.
• WSF CamagN (13.5-0-0 + 16% CaO + 6% MgO): water-soluble calcium magnesium nitrate for fertigation; keep it in its own tank, away from phosphates and sulfates.
• LS Calcio Max 40 (40% CaO): a concentrated liquid calcium suspension for foliar use.
• LS Calcimag Liquid (12.5% CaO, 2.5% MgO, 8% nitrate N): liquid calcium with magnesium for foliar programs.
• SM Ca EDTA 14% (14% CaO as EDTA chelate): chelated calcium; use as directed on the label.

All are produced to Van Polder specifications. Follow the product label for rates, and base calcium programs on soil and leaf analysis.

FAQ

What is the best calcium fertilizer for plants?

It depends on the goal. Lime corrects acid soil and adds calcium; gypsum adds calcium without raising pH; calcium nitrate is the usual soluble source for fertigation; and liquid calcium or calcium-boron sprays target fruit and young tissue directly (Mittenthal et al., n.d.; Fernández et al., 2013).

Does liquid calcium fertilizer work?

Yes, on the tissue it reaches. Repeated preharvest sprays reduced bitter pit and improved storage in apple (Yamane, 2014), but calcium sprayed on leaves does not move to the fruit (Hawkesford et al., 2023), so aim sprays at the fruit and start early.

Why do my fruits show calcium deficiency when the soil has plenty?

Calcium moves with water to the leaves, not to the fruit, and fast growth, high potassium or ammonium, high humidity and drought all reduce the share that reaches fruit (Kutman, 2023). Even watering and balanced nutrition matter as much as the calcium source.

Is calcium nitrate a good calcium fertilizer?

For fertigation, yes: it is highly soluble and supplies nitrate nitrogen with the calcium (Robinson & Galán Saúco, 2010). Keep it in a separate tank from phosphates and sulfates (UC Agriculture and Natural Resources, n.d.).

What are the downsides of calcium nitrate?

It supplies nitrogen as well as calcium, so count it in the crop’s nitrogen plan: high nitrogen speeds growth and dilutes calcium in young tissue, which can make calcium disorders worse (Kutman, 2023; Gerbrandt et al., 2019). It also cannot share a stock tank with phosphate or sulfate fertilizers (UC Agriculture and Natural Resources, n.d.).

Which fertilizer has the highest calcium content?

Among common sources, hydrated lime has the most calcium (46.1%), followed by calcitic lime (31.7%), gypsum (22.5%), dolomitic lime (21.5%) and calcium nitrate (19.4%) (University of Maryland Extension, n.d.). The highest figure is not always the best choice: lime and dolomite also raise soil pH and do not dissolve in water, so for feeding during the season a soluble source such as calcium nitrate is more useful.

What is the fastest way to add calcium to soil?

Use a soluble source. Calcium nitrate dissolves readily, about 102 kg per 100 L of water at 20 °C, and can be applied through the drip so it reaches the root zone with the irrigation water (Robinson & Galán Saúco, 2010). Gypsum dissolves slowly and lime does not dissolve in water; lime is for correcting soil acidity before planting, not a quick calcium fix (Mittenthal et al., n.d.).

Does homemade calcium for plants, like eggshells or seashells, work?

Yes, but slowly, and as a liming material rather than a calcium feed. Eggshells are about 94% calcium carbonate, roughly 38% calcium, the same compound as ground limestone (Waheed et al., 2019). Oyster and scallop shells are 95–99% calcium carbonate, so they too work as slow liming materials rather than quick calcium (Seesanong et al., 2023; Thongkam et al., 2021). Finely ground, they raised the pH of two acid soils as much as agricultural lime at the same rates (Sebonela et al., 2024). In groundnut, 300 kg/ha of eggshell powder gave a higher pod yield than 500 kg/ha of lime when it was worked in before sowing, but applied after flowering it gave lower yields (Vu et al., 2022). Soaking shells in vinegar turns the carbonate into soluble calcium acetate (Strelec et al., 2023), but the calcium content of a homemade brew is unknown, and like any calcium foliar spray it only helps the tissue it wets. Use eggshells as a slow soil amendment before planting; for calcium during the season, use a soluble calcium fertilizer.

Next step

Test the soil for pH and calcium before planting, then check leaf analysis for calcium together with potassium and magnesium. For calcium in banana, start with our guide to fertilizer for banana plants. For help choosing calcium products for your crop, contact your Van Polder distributor.

Sources

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