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Plant Answer Line Question

Keywords: Tomatoes--Diseases and pests, Soil amendments, Plant-water relationships

It's summer and my husband wants to add lime to our soil because some of our tomatoes have blossom-end rot. He thinks this will correct the problem. I think we would do better to make sure our tomatoes aren't drying out, and then work in soil amendments next time around. Also, couldn’t we use eggshells for calcium instead of lime? We have a ready supply from our backyard chickens!


I think you are on the right track. Blossom End Rot (BER) is a physiological disorder that tends to affect larger tomatoes rather than smaller ones. According to Craig LeHoullier’s book Epic Tomatoes (Storey Publishing, 2015), some varieties are especially susceptible: "Roma/paste varieties, and some of the longer indeterminate sauce types like Opalka and Speckled Roman. Adverse growing conditions [such as drought stress or low calcium levels] can make it problematic for many other varieties as well."

All print and web sources I consulted mention environmental conditions as a cause of this problem. It starts through the supply of water and calcium in the developing fruits. The effects may be seen on plants exposed to a period of drought during rapid growth; root damage; heavy, wet, or cold soil; excess salt in the soil.

A soil test is the ideal starting point to make sure the pH is adequate for tomatoes. Epic Tomatoes recommends amending the soil with lime if necessary. (Washington State University Extension says the time to do this is 2-4 months before planting, not in the middle of summer!) Mulch around the base of the plants to conserve soil moisture during hot spells and water regularly. Another reason a soil test is a good idea is mentioned by British Columbia author Linda Gilkeson in her book Backyard Bounty (New Society Publishers, 2011):
"Your soil might have enough calcium, but it isn't available, or the plant can't take it up fast enough. This is often because the movement of calcium inside the plant has been inhibited by drought stress, possibly from irregular watering. This is often seen on tomatoes in containers that experience alternating dry and wet soil. It can also be caused when plants grow too fast as a result of too much nitrogen fertilizer."

Since you prefer not to use lime (the dry powdery texture of calcium carbonate can be irritating to the skin and eyes), you will be pleased to know that the use of eggshells is mentioned by Mike McGrath in You Bet Your Tomatoes! (Rodale Press, 2002). At planting time you can "put some crushed-up eggshells into the planting hole." Make sure the eggshells are ground to a fine consistency.

Don't forget that those damaged tomatoes can still be used--just cut off the bad parts!

Date 2018-03-14
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August 01 2017 12:36:01