The recommended time to apply gypsum on peanuts is early bloom, which normally occurs around 45 days after planting, or maybe as early as 30 days after planting.
How late is too late to apply gypsum?
Again, since the “peak pod fill” period is 60 to 90 days after planting, and this is the time when developing pods are “sucking in” calcium dissolved in the soil solution directly through the hull, once you get to 100 days after planting, it is definitely too late to apply gypsum.
What about 60 days after planting? Well, 60 days after planting is better than 70 days after planting, which is better than 80 days after planting. You get the idea.
Two other things to keep in mind if you are considering a late, or 60-90 days after planting, gypsum application:
• Will you do more damage running over lapped vines than you gain by adding calcium?
• Did you really need a gypsum application in the first place?
Remember that if you had at least 500 pound per acre of soil test calcium in the pegging zone (top 3 to 4 inches of soil) AND a calcium-to-potassium ratio in this soil sample of at least 3:1 or better, AND you are not producing peanuts for seed, than you technically did not need a gypsum application at all.
I hear about many soil samples being in the 700, 800, 900 even 1,000 pounds of Ca per acre range and with all the rainfall we have had there should be plenty of soil water in the pore space to dissolve the soil calcium and get it into the nuts.