Answer: It isn't unusual for newly planted trees (especially large ones) to go through some transplant stress. A few yellow leaves should not be reason for concern. As the roots become established (which may take several weeks), expect your new tree to look pathetic. Once the roots are firmly established, it should perk right up. Mimosa trees like a deep soaking once a week (or twice - depending upon weather). You can check the soil moisture level to make sure your drip system is doing an adequate job by digging down near the roots. If the soil is moist 3" beneath the surface, everything should be alright; if it's dry, you'll need to apply more water; if the soil is soggy wet, you could suffocate the roots by eliminating all the oxygen. If this is the case, you might want to readjust your drip system.
Best wishes with your new tree!
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