Hardly any plant is off limits to deer, but gardeners can employ a few techniques to help keep them away from summer gardens.

Familiar with human activity, perceptive deer observe behaviors that enable them to work around deterrents. While there aren’t many foolproof ways to keep deer out for good—aside from 10-foot-high fences—homeowners can angle a shorter fence 45 degrees to give an illusion of a higher one or install two five-foot-high fences four feet apart.

“Deer don’t have the ability to estimate distance correctly, so the fences will look closer and higher than they actually are,” said Kirsten Ann Conrad, a Virginia Cooperative Extension agriculture and natural resources agent in Arlington. “They won’t risk getting caught between the two fences, so they’re less likely to jump.”

While not everyone can invest in fences, and some localities may not allow it, gardeners also can try non-toxic deer repellents.

“These sprays are generally effective if they’re applied earl...