I would wait until the start putting up their first shoot or two, then gently remove them from the ziploc bags and plant then in a good organic potting soil in 1 gal. pots. Leave them in these pots until they are 1.5 - 2ft. tall, then step them up to 3 gal. pots and leave them in those until they are about 3.5ft. tall. At that point, you can plant them in the ground. This may take several years for them to get to that size as they are a fairly slow growing palm, but they should do well in Galveston. Water them every other day when you transplant them for the first week and a half, and after that twice a week should be adequate. Once they are in the ground and established, give them a deep watering once a week.