We just bought a rams horn willow from a local farmers market. We have been told that they can grow up to 25 plus feet. We were also told by keeping it in a pot it will stay small and ornamental, which we prefer. Id it's about 8 feet tall now in a half whiskey barrel . How do we proceed to help it bush out more. What and when to prune and how often would be helpful. Thanks
I'm sorry to say that, assuming you mean Salix babylonica 'crispa', common name Rams Horn Willow, its ultimate height and spread is around 12 metres or 40 feet, with a spread of about half that height. Even with rigorous and hard spring pruning, it is not going to be happy in a pot ongoing; if your tree already lacks bushiness, its likely the roots are cramped and this is reflected in poor topgrowth.
Prune it back hard in spring, see how it does. If you're able to add a photo of the plant, it will be easier to tell whether its growing well or if its suffering.
Willows are one of the most indestructible trees there are. Whatever you do to it, you will have a hard time killing it!
Willows are the only tree species where literally any old log of dry willow wood, with no roots or leaves, will start to grow if you just put it in a bucket of water for a few weeks, and give it no "tender loving care" whatever.
But if you have a willow species that wants to grow 40 feet tall, trying to confine it in a pot isn't going to end well. It won't necessarily die, but it will look pretty miserable. The main problem is that it won't get enough water - unless you literally give it a gallons of water every day, to compensate for the fact that the roots can't go deep in the ground and get down to the water table. (Actually, they might end up deep in the ground, simply by punching a hole through the bottom of your wooden barrel...)
Remember willows grow naturally in places like river banks, where the roots can get directly into the water. A garden isn't their natural habitat at all.
Of course trying to give a plant in a "small" pot gallons of water per day means you will have to water it several times during each day, not just once - which probably isn't a practical idea, unless you want to set up an automatic watering system and leave it permanently switched on.
You could try coppicing it, to get several small trunks rather than one big one. Just saw the existing trunk off 6 inches above ground level in spring when the tree starts coming back to life after the winter, and wait! I already said they are almost impossible to kill - even if you fell a big willow tree and the n attack it with a stump grinder to take out everything down to a foot below ground level, there's a 50-50 chance it will re-grow again.
After that, cut out as many trunks each year as you need to keep it under control - but the end result isn't likely to be very satisfactory even then.