Water,water,water!!!

Hmm! So I can let hosta roast in heat and sun as long as I water enough?

They may still get crispy, but they'll live. Did the tree go down this season?

The locust tree went down several years ago, but I have maintained the area as a bright shade garden. The hosta went in over the last two years. The new shade is being provided by shrubs and small trees. I guess the scorcher is the few hours of afternoon sun. The overall effect is very lush and lovely for a couple of early summer months, but otherwise either bare in winter or parched in August. I have several other places that are the same conditions, basically bright shade for most of the day with a blast of afternoon sun enough to burn hydrangeas. It's tricky. You need plants that don't require full sun, but can withstand a few hours of it in a strong does. Locust trees, with very high dappled light, were obviously perfect, but not to be replaced so close to the house.

Lots more water will help. Plus some hostas are more sun tolerant than others.

Sun tolerant hostas

More water is the main thing, but a light colored mulch will not only help retain moisture, but will keep the roots a bit cooler. Don't mulch right up to the base of the plant, leave a couple of inches bare to prevent any fungal issues.

When you water, be sure that you water deeply. Shallow watering encourages shallow root growth, which is not going to help sun stressed plants.

You might consider a temporary pergola, it's fairly easy to put one up using crosshatched trellis material, either in wood or plastic. Or you could use a simple frame and put up shade fabric.

Eventually many hostas will adjust perfectly well to full afternoon sun. Those that do not can be swapped out for varieties that will perform better under your conditions.

I have 5 mature (150+-year-old) oak trees on the east edge of my garden that normally shade my front garden beds & my many hostas until early afternoon. Gypsy moth caterpillars stripped the trees back in mid-June so all my hostas were suddenly exposed to full sun right around the summer solstice. All are mature plants with well developed root systems but the sun was strong. I watered them using recycled plastic gallon milk jugs with a pinhole punched (with an ice pick) an inch from the bottom opposite the handle. I filled the jugs with water, set them at the base of my plants so they were watered slowly, gently. Water remaining once the level fell below the pinhole held the jug in place.

Sorry I don't have photos to show but all my hostas are alive and thriving. I think we've had a total of two rain showers so far this summer along with a whopping ONE thunderstorm.

kitasei - I'm in southern New England so not that far from you.

What is the best way to deal with it when it gets like this in August?

I've lived here since I was 12 and no two years have ever been the same. I just give them healthy soil, adequate moisture & hope the healthy* soil & roots keep them alive until the weather gets back to normal.

* My parents practiced organic gardening here for 40 years before I moved back in 2005. I continue to honor their commitment.