Gabe15

From the basic description of the soil you provide, a large quantity of compost or composted manure, or even just manure, would be immensely helpful. If you can, a wheelbarrow or so full for each plant would be excellent mixed into the holes you bud, and since it is early there will be no consequence of pulling out the plants to do this and replanting. This will provide a lot of nutrients of course, but will also improve the ability of the soil to hold other nutrients for use by the plant, improve water availability and many other beneficial things.

Also, plant the pups deep. It is even beneficial to have the bottom of the sucker 2ft or more below the soil surface, provided it is tall enough to stick out a little bit. This allows the plants better access to a more even water supply and helps keep the roots cool in such hot temperatures. But this will only be helpful if the hole is very deep. If you could make the holes about 1m wide and 1m deep, put in the wheelbarrows amount of manure, and mix in the other soil you have added and some of the native soil, you will essentially have created an in ground container large enough to fruit the plants in, and they should grow very well provided enough water. Even if you are not there long enough to see them fruit, they will grow extremely quick.

And lastly, mulch the soil surface with something to keep the soil surface cool, keep water in, and keep weeds out (since you will be watering it, you should expect other plants to take advantage of that too). This can be as fancy as woodchips or bark or as simple as cardboard with rocks to hold it down. Also cut grass leaves work great too, just sometime to cover the soil surface is always helpful. Banana leaves are excellent, free and easily available once they get going and start shedding old leaves.

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Growing bananas in Colorado, Washington, Hawaii since 2004. Commercial banana farmer, 200+ varieties.