Tricks to help a plant to not dry up so fast

Hello all. I have 5 Gas cross mom's that I recently put outside. I dug large holes (2 foot wide and 3 foot deep) and filled them with soil. I am only able to water one time a week. It's been in the high 80s and low 90s here so I'm looking for tricks to keep the soil moist as long as possible. Someone told me to add hay over top of the soil any other recommendations?

Thank you

Yes a thick layer of hay/straw works great. A week in hot weather is still asking a lot though.

Hay or even black plastic. Both helps preserve moisture and keep weeds out. Straw better than hay. Hay can sprout weeds etc. Vermiculite mixed into the soil before planting helps retain moisture throughout .

You can take 5 gallon buckets and put a few small sized holes at the bottom of it. It will slowly release the water.

For future grows add polymer crystals to your soil.