How to Make Calcium Spray for Blossom End Rot? | Foliar Fix That Works

To make a calcium spray for blossom end rot, mix 2 tablespoons of calcium chloride in 1 gallon of water and spray leaves and fruits thoroughly.

Blossom end rot shows up as a sunken, leathery dark patch on the bottom of tomatoes and peppers, and it almost always comes down to a calcium delivery problem. The plant either can’t pull enough calcium from the soil or moisture swings keep it from moving calcium where it’s needed. A homemade calcium spray puts calcium directly on the foliage and fruit so the plant can use it without waiting on the roots, but it matters how you mix it and when you apply it.

The mix is simple, the timing is specific, and the spray is a corrective measure rather than a cure for the underlying moisture issue. Here’s the working recipe and the rules that keep it from doing more harm than good.

The Standard Calcium Chloride Recipe

LSU AgCenter recommends mixing 2 level tablespoons of 96 percent calcium chloride in 1 gallon of water. Oregon State University Extension gives nearly the same ratio at 2 tablespoons per gallon. Spray the solution onto both the leaves and the developing fruit until they’re thoroughly coated.

Apply this spray late in the day, early in the morning, or on a cloudy stretch when the sun is low. Calcium chloride can burn leaf tissue when it dries under intense sun, so the timing isn’t a suggestion—it’s part of the method. LSU warns that overdosing the mixture raises the burn risk, so stick to the measured ratio.

How Often Should You Spray?

One application isn’t enough to protect new growth. OSU’s guidance is to spray thoroughly when symptoms appear, then repeat twice more at 1-week intervals. LSU’s schedule is similar: apply at 7- to 10-day intervals for 3 to 4 total applications.

Both schedules assume you’re treating active symptoms on plants that are still setting fruit. New blossoms and small fruits need coverage as they form, and the calcium you sprayed last week won’t still be on the surface of this week’s growth.

Calcium Nitrate as an Alternative

Calcium nitrate works as another source, and LSU AgCenter gives two ways to use it. For a foliar spray, mix 2 level tablespoons per gallon of water and apply late in the day. For a soil application, work 1 rounded teaspoon per plant into the root zone.

Both extensions emphasize the foliar route for active symptoms, since it bypasses whatever is blocking root uptake. That said, LSU notes the soil application has merit for getting calcium into the plant’s system over a longer period, and neither source suggests skipping the moisture correction while you spray.

What the Spray Won’t Fix

Calcium sprays treat the symptom but not the cause. OSU is direct on this point: correct soil moisture problems at the same time, or the rot keeps coming back. Blossom end rot is driven by uneven watering—drought stress followed by heavy irrigation—which interferes with calcium transport even when the soil has plenty of it. The spray keeps new fruit alive while you even out the watering schedule, but it doesn’t undo damage already done. Affected fruits stay scarred and won’t heal.

After you spray, keep irrigation from washing the residues off the foliage. The calcium needs time to absorb, so water at the soil line rather than overhead for a day or two after each application. If you’re buying a commercial product instead of mixing your own, our tested roundup of the best calcium sprays for blossom end rot covers the options that work in practice.

Blossom end rot is a moisture-management problem with a calcium-spray symptom. Oregon State University’s factsheet on blossom end rot walks through the full diagnosis and treatment sequence. Use the spray to buy time, fix the watering to end the problem, and the new fruit will come in clean.