That idea is great, but my grandmother built up 'soil' collars around her plants and that worked well. She grew a lot of herbs, begonias, some pomegranates and a large Rue. I've read about putting plants on mounds so not to get too much water and planting them just a little below the soil line if they need more water. But I've been satisfied with building a 'soil' collar, as you've described. Here in Vacaville, the summers are really hot and dry, so I totally understand your need to make sure new plants get the water they need. Glad you found a good temporary solution.