Here’s a bit of research from Utah State University I found interesting and practical for those who grow a fall crop of vegetables either in the garden or in cold frames
Researchers Benjamin Hudson and Dan Drost grew spinach and lambs-quarters in high-tunnels (a tall cold frame) and found that covering with a frost protector such as Remay, significantly increased yields over non-protected crops while actually heating the soil didn’t create any increase in harvest
Bottom line — use a frost protector fabric in the fall or inside winter greenhouses to increase the harvest of edible green crops
An Important Point For Home Gardeners About The Early Spring Crop
A second trial was done with very early spring crops and the spacing was altered. With this early crop (not with later crops) the harvest increased by moving the plants to a closer spacing (yields up by as much as 48%) from the normal 6-inch spacing to a tight 2 or 4-inch spacing
Bottom line — an early crop or greens can be crowded because of temperatures and you can harvest leafy greens earlier and regularly through the growing season.
Do NOT do this during the regular growing season as the increase in leaf diseases from crowding (leaf diseases are more prevalent during warmer weather) will reduce harvests instead of increase them.