Answer: I wish there were a magic formula for watering, but there are so many things to consider, that it's impossible to give absolute answers. Some plants naturally require more water than others; soils can make a difference in how much of the water you apply is retained; current weather factors into it, too. Sandy soils drain very quickly; clay soils retain water longer; extreme heat will affect watering frequency, as well. With that said, both oleander and flax are relatively drought tolerant and should be happy with about one-inch of water per week during the growing season. I'd dig a water well or basin around each plant, extending out at least 12". Fill the basin with water, allow it to drain, then fill it a second time. This method of watering concentrates the water directly above the root mass and allows it to trickle down, wetting the entire root mass. Once a week should do it; twice a week if weather is exceptionally hot.
I cannot locate a Purple Bottle Brush plant in any of the retailers in your local vicinity. Sorry!
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