Hi, welcome to GoY, you should water sparingly in winter under glass, wait until the top of the compost feels dry, you don't say where you are in the USA, but Albizia julibrissin, commonly referred to as the silk tree, can withstand temperatures down to minus 4f for short periods, below this you will need winter protection, otherwise it would be quite happy outside, in a position sheltered fromcold winds, Derek.

If it's the Albizia julibrissin (Persian Silk Tree), be aware that it can grow to 50 ft tall.

There is also the silk oak...Grevillea robusta

when soil is dry-simple as that guys.
(some times dig a little deeper as the under layer may be moist :)

many thanks guys-very helpful