A: Strictly speaking, mid to late fall is the best time of year to get plants into the ground. This is because you do not have to worry about the plants immediately having to endure a hot Texas summer, and because the root systems of plants are very active during the winter. So, plants planted at this time of year tend to do best the following year. Unfortunately, Austin is prone to one or two hard freezes each year, and some Texas native plants are more susceptible to these freezes than others. Still, planting before winter is generally better than planting before summer. (Except, of course, in the case of annual plants, which are expected to die out in the winter.)
But, if you have an irrigation system to support your plantings, we generally advise planting without worrying about what time of year it is. After all, Texas native plants in particular, so long as they are watered, are equally threatened by a hot summer or cold winter.
Aside from plants, there really are no aspects of landscaping that cannot be done any time of year. So, for the most part, the best time of year to do great landscaping work is the time of year you decide to have us do it!