Issue: July 1, 1996

Squash blossom-end rot

Question: I have yellow straightneck squash that get about two and one-half inches long, then get blossom-end rot. My white patty-pan squash get about two inches across and then dry up. Please tell me what causes this and what to do for it.

Answer: When you read the garden books and often the news articles taken from the national news services, you will read that blossom-end rot is due to a lack of calcium. Gardeners familiar with New Mexico's soils realize that our soil is not deficient in calcium and wonder how they could get blossom-end rot. The answer is that though we have an excess of calcium, we have a deficiency of water and extremely desiccating environmental conditions. Calcium travels through the plant in the water. Dry soil, hot, dry, windy days, or anything else that prevents water from reaching all parts of the plant can limit the movement of nutrients in the plant. Hot, dry, windy days, or a brief period when the soil drys disrupts the flow of water and nutrients through the plant. When this happens, the small developing fruit loose their supply of water and calcium. As the fruit enlarges, the brief deficiency of water and calcium becomes apparent as blossom-end rot.

Dr. George Dickerson, Extension Horticulture Specialist for vegetable crops, small fruits, and speciality crops, suggests that care be taken to keep the soil evenly moist and the use of mulches to reduce the evaporation of water from the soil. Be sure you don't over compensate with irrigation and keep the soil soggy - this will cause other problems. Shelter from the afternoon sun and from the drying winds can also reduce the incidence of blossom-end rot.

Dr. Dickerson also said that some diseases, including curly- top virus can cause the symptoms you describe. These symptoms include fruit that fail to grow, get hard, and develop blossom- end rot. There may also be leaf symptoms that mimic 2,4-D herbicide injury. He has seen the development of these diseases in Southern New Mexico this year. Generally, when several plants are growing in a row, one or a few will be affected and be stunted compared to the others. This helps distinguish the disease symptoms from herbicide injury.

Still time to plant

Question: I was too busy this spring to plant a garden and since it was so dry I didn't worry about planting one. Now that it has finally begun to rain, is it too late to plant a garden?

Answer: No, now is a good time to plant a number of vegetables and flowers. Planting in the heat of the summer is the best time to plant crops that taste best if harvested in the cool temperatures of autumn. Broccoli and cauliflower are examples of vegetables which are best harvested in the autumn. Other plants that grow rapidly and love heat can also be planted now. Squash is a good example of a vegetable that does well in the heat.

The following calculation will help you determine what you can plant now: Check the seed packet to determine the number of days to frost, then look at your calendar and count the number of days until frost is expected in your location. Add a week or two for harvest time and then you will know if you have time to plant a garden.

Some crops like broccoli, kale, mustard, collards, and other "cool-season" crops will not be killed by the first, light frosts. Their growing and harvest season will extend until a hard freeze kills them. You can cover them to protect them from the early frosts, so they give you even more time than the calculation we discussed would indicate.

If the monsoons persist, our high temperatures should begin dropping and the plants should grow well. Even if the temperatures remain high, afternoon shade and wind protection will help get plants going in our hot weather.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email:, office: 505-865-7340, ext. 113.


For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at, or at the Desert Blooms Facebook.

Please copy your County Extension Agent and indicate your county of residence when you submit your question!