Every year I seem to have calcium diffiences at the end of my crop which causes weak stems and breakage. I prevent bract burn with Cal sprays. I wanted to try and add cal to my mix before planting but not move my ph it was suggested to use Gypsum (calicum sulfate) at 1.5 to 2 pounds per cu yard of soil. What I found at my local co-op is called sof'n-soil lawn& garden Gypsum. It has an analysis of:
Calcium sulfate as CaS04-2H2o
Minimum Calcium Equivalent 19.3%
Minimum Sulfate equivalent 15.4%
Is this ok to use with poinsettias.

Thanks

Low levels of calcium in the tissue can be caused by many different aspects of production so we should review those reasons and it may be possible that a preplant amendment to your media may not be needed.

Calcium could be low in the tissue because:

Root rotting has decreased nutrient uptake. Overwatering can also lead to damaged roots and reduced uptake of nutrients.

Cool growing temperatures have reduced the flow of certain immobile nutrients such as calcium. Calcium requires the flow of water through the plant to move. Cool growing conditions slow the plants transpiration rate and the amount of water moving through the plant, sometimes resulting in a calcium deficiency.

The relative humidity is too high or the weather is overcast. When transpiration rates are reduced from these conditions calcium won't be moving through the plant as much.

High levels of magnesium in the media have inhibited the uptake of calcium. Throughout production when you supply calcium and magnesium it should be at a 2:1 ratio. High potassium, ammonia, and sodium in the media or irrigation water can also inhibit calcium uptake.

Calcium levels are low in the media. This may be because there is little or no calcium supplied in your irrigation water, leaching is excessive, or there is an insufficient initial lime charge in the media.

Gypsum or calcium sulfate will supply and extra source of calcium without raising the pH of the media. However in addition to the calcium it is also supplying sulfur. Excess sulfur on a poinsettia crop can accentuate potassium, calcium, or magnesium deficiencies. It looks like the mix you found supplies almost equal amounts of sulfur and calcium. The better way to go may be to evaluate the other factors that can lead to low levels of calcium in the tissue and see if anything can be adjusted rather than using the gypsum which may lead to other issues. Hope this helps.....

Thank you for using Ecke Ranch Tech Help on-line!

This may seem like a stupid question but if high potassium can inhibit Calcium uptake, why do they sell Poinsettia feeds that have higher potassium levels (for example 15-5-25)?

I had this soil and leaf tissue analysis results for poinsettia , but frankly they mean nothing to me , can anyone help me if the nutrient levels are ok ( note these were taken by the end of september last year
leaves: total N 0.2%, total P as 916 mg/kg , K 0.36%Ca0.3%,Mg 5mg/kg, Fe 153mg/kg
Soil: Ph 7.5, Ec: 243us/cm, total nitrates0.3%,Ammonical nitrogen<0.1% ;total P 249 mg/kg, K 8mg/kg; Fe156mg/kg