Calcium (Ca)

Function:

Calcium (Ca) is a major constituent of cell walls. Ca is a non-mobile element and uptake is by the root tips.

Deficiency:

Deficiency symptoms are expressed as death (blackening) of growing points of terminal buds and roots. Young leaves may be chlorotic and have upward puckering of leaf margins. Low levels of Ca have been linked to weak stems and the resulting stem breakage. The most common concern with poinsettias is leaf scorch and bract edge burn. It is important to correct Ca deficiency when symptoms first appear because leaf scorch or bract edge burn can not be reversed. Ca is a non-mobile element within the plant, therefore deficiency symptoms will first appear on the upper, younger leaves.

Ca deficiency symptoms of younger leaves.
Click on image for larger version. (image ©Paul Nelson, NCSU)

Bract edge burn symptoms on Supjibi poinsettias.
Click on image for larger version. (image ©Brian Whipker, NCSU)

Bract edge burn symptoms on poinsettias.
Click on image for larger version. (image ©Robert Eddy, Purdue Univ.)

Excess:

Can reduce uptake of: potassium (K), magnesium (Mg), or boron (B).

Confirm your actual Ca levels by conducting a routine root substrate (medium) test and/or a plant tissue analysis.

Monitoring and Management Strategy for Calcium (Ca) Fertilization Rate:

75 to 125 ppm constant liquid fertilization rate and follow the Bract Edge Burn Prevention guidelines listed below when bracts begin to color. See the Fertilization Rate Table for specific fertilization recommendations based on growth stage and irrigation practices.

Ratio:

Calcium (Ca) fertilization rates >200 ppm can have an antagonistic effect on K or Mg uptake by the plant. Supplying the plants with a K : Ca : Mg ratio (ppm) of 4 : 2 : 1 will limit any antagonisms.

Tissue Concentration:

Normal range of 1.0 to 1.75%. Levels below 0.5% are considered deficient.

Options:

Preplant:

Application of dolomitic limestone.

Irrigation Water:

Ca in irrigation water (test water to determine available levels) Supplement with additional Ca in your fertilization program.

Continual Fertilization:

1. Use a fertilizer that provides Ca. Examples include calcium nitrate (Ca(NO₃)₂), Excel® 15-5-15 Cal-Mag, and others. Calculate the ppm of Ca provided and make supplemental applications of calcium nitrate (Ca(NO₃)₂) if required.
2. Common fertilizers like 20-10-20 and 20-20-20 do not provide Ca (or magnesium [Mg]). If using 20-10-20 or 20-20-20, alternate every third fertilization with calcium nitrate (Ca(NO₃)₂) at 200 ppm of Ca. (Also apply supplemental Mg.)

Corrective Fertilization:

1. Supplemental applications of calcium nitrate (Ca(NO₃)₂) at 200 ppm of Ca. Visible improvements with the use of the corrective Ca fertilization should evident on the new growth within 2 to 3 weeks. Do not over apply. It is important to correct Ca deficiency when symptoms first appear because leaf scorch or bract edge burn can not be reversed.

Additional:

Remember that Ca uptake into the plant and transportation within the plant is through the water flow, so promoting good root growth so water uptake can occur and good shoot growth that aids in transpiration will assist in Ca uptake.

Bract Edge Burn Prevention:

Start weekly applications of calcium at 400 ppm from when bracts begin to color and bracts are still expanding until pollen shed. Spray enough to just wet the bracts. Apply early morning or late afternoon. Consider using reagent grade chemicals to assure purity and avoid possible leaf burn, especially on the bracts.
Option A. Calcium chloride (CaCl₂· 2 H₂O): mix 1.47 grams per liter, or 5.6 grams per gallon, or 0.196 oz per gallon.
Option B. Calcium nitrate (Ca(NO₃)₂· 4 H₂O): mix 2.36 grams per liter, or 9.0 grams per gallon, or 0.31 oz per gallon.

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