Hi, 

You could hold off on the Miracle Gro for now. It probably won't hurt the tomatoes but any extra nutrients the plant doesn't need will just not be used and have potential for washing off.  A slow release granular fertilizer may be more beneficial at this time and just be sure to water regularly so ward off blossom end rot or other stress responses due to the heat. 

You can visit our Growing Tomatoes page and there is a bullet point about fertilizer and additional link that may be helpful. 

Let us know if you have further questions. 

Emily