Short answer: for most Austin tree companies, nothing. The words are used interchangeably and a quote headed “trimming” will include work anyone else would call pruning.
Where a distinction is drawn, it is this. Trimming is cutting for clearance and appearance: getting limbs off a roof, lifting a canopy over a driveway, tidying a shape. Pruning is cutting for the health and structure of the tree: taking out dead, diseased, crossing or badly attached limbs.
Any competent job does both on the same visit, which is why arguing about the label wastes everyone’s afternoon.
The words that do change the price
These four matter, and they are what you should actually be asking for.
Crown cleaning. Taking out dead, dying, diseased and broken limbs and nothing else. The lightest job, safe at any time of year for any species, and often all a healthy tree needs.
Crown raising. Removing lower limbs to get clearance over a roof, driveway, footpath or street. This is what most Austin homeowners actually want when they call. Ask for it by name and the quote gets smaller.
Crown thinning. Selectively removing branches through the canopy so wind passes through rather than pushing the whole tree. Genuinely useful on the clay soils east of I-35, where root plates work loose and a dense canopy acts like a sail.
Crown reduction. Shortening the overall size by cutting back to lateral branches large enough to take over. Real work, done properly, and completely different from topping.
Topping is not pruning
Topping means cutting main leaders back to stubs with no regard for where the cuts land. It is the one thing in this article worth being dogmatic about.
The tree responds to losing that much canopy by pushing out a dense flush of upright shoots from around each wound. Those shoots attach poorly, grow fast, and break out in wind. Meanwhile the stubs cannot seal properly, so decay moves into the trunk. Three years on you have a denser, weaker, uglier tree and the same problem you started with.
If a crew quotes you for topping a live oak or cedar elm, get another quote. Crown reduction achieves what you wanted and does not wreck the tree.
Where the cut goes
Every cut should finish just outside the branch collar, the slightly swollen ring where a branch meets the trunk. That collar contains the tissue the tree uses to seal the wound. Cut outside it and the tree closes over in a season or two.
Cut flush to the trunk and you remove the collar, so the wound cannot seal and decay walks inside. Leave a long stub and it dies back, which does the same thing more slowly. Both are visible from the ground a year later, which makes it an easy way to judge work you have already paid for.
Timing, which matters more than terminology
In Central Texas one rule beats everything: no oak pruning between February 1 and June 30, because of oak wilt, and paint every oak wound the same day whatever the month. Cedar elm, pecan, hackberry and juniper have no closed season.
Mid-winter is best for almost everything else. Details in the best time of year to trim trees in Austin and can trimming an oak kill it.
How much to take
No more than about a quarter of the living canopy in a season, less on a mature or stressed tree. Leaves are how a tree feeds itself, and an Austin summer is demanding enough without the tree starting it short of them.
Not sure which of these your tree needs? Send a photo and say what is bothering you. See tree trimming in Austin, plus Round Rock and Cedar Park.