Just another reminder that even though we haven't reached really concerning temperatures yet, temperatures in high tunnels, crops under rowcovers or especially those under clear plastic hoops (such as sweet corn) can get very hot on these gorgeous bright sunny days!   For sweet corn, the larger the plant under that plastic the greater the risk of injury is.  If it gets too hot under that plastic, consider piercing the plastic with a pitchfork or setting up and running the irrigation to cool the soil and plastic.  If it looks like we are in for a long warm stretch, you might consider slitting the plastic and removing it altogether.  The one benefit of using floating rowcovers on sweet corn compared to plastic is you don't have to worry about it getting too hot as the rowcovers naturally breathe and are cooler.  The following information is from Dr. Steve Reiners of Cornell University Department of Horticultural Sciences and can be used as a guide to know when to remove covers before it's too late! 

 "Most of the published temperature guidelines list maximum temperatures at which either vegetative growth becomes limited or reproductive capabilities are threatened, i.e. flowers or fruit fall off. Temperatures at which vegetable plants may die varies and depends not only on the vegetable type but also on other factors such as whether irrigation is being provided or for how long the high temperature occurs.  Also, a transplant will be under much greater stress than a plant that is direct seeded. 

The following table lists temperatures at which severe stress will occur, possibly death, especially if soil moisture is low.  These temperatures refer only to potential crop death.  Temperatures 15 to 20F lower than those listed in the table will result in the loss of flowers and fruit and will negate the positive effects of early warming under row covers."

Chart with various vegetables

Row cover