Rosemary is a herb extensively used in cooking. If the plant is not being used extensively, and you want to control the growth, then you will have to start regularly pruning. Here are soem tips for successful rosemary pruning.
Tip #1 - New Growth Only
The one rule that you must abide by with rosemary is never to cut older, woody stems. Some plants will tolerate this, but rosemary will start to die. Only take off up to five inches at a time. The best time to prune rosemary is early spring or late in the fall, but regular attention to stems that are growing too long will keep the plant in order.
Tip #2 - Make a Tree
Rosemary can grow very large for a shrub and many gardeners like to prune them so that they look like small trees. As the plant grows, the shoots off the bottom of the main stem should be removed. As the growth continues the growing tips of the other stems should be snipped off. This will encourage lateral growth and you will soon have a very bushy top. The plant can be left to grow naturally or be trimmed back once it reaches the ideal size.
If clipping for culinary use or for drying, do not use any stems that were pruned in the last two or three weeks.
Tip #3 - Make a Shape
Rosemary can be trained into just about any shape you want. Instead of using wires or frames to get the effect that you want, start the shape planning as soon as the bush is big enough. It is best to let the shrub grow into the shape that you want. Try to envisage the shape and then only clip those stems that project outside the image you create. Some stems will appear to be growing at a faster rate than the others. Although not suckers these stems behave like suckers and should be cut right back.
Tip #4 - Don't Worry about Mistakes
Because rosemary grows so prolifically there is little chance of making a mistake with your pruning. Even pruning the shrub right back will often see the plant recover very quickly. The next time you prune you will know what not to do.
Tip #5 - Constant Attention
Probably the best way to keep a rosemary bush in order is to start out with regular small scale pruning. The bush grows quickly and to snip it into shape as it grows can solve a lot of problems. Pruning once a year is not really necessary if the plant is allowed to grow into the shape that you want and controlled by weekly attention. The only time you should not prune is when the plant is flowering.
If your rosemary is in a pot or container, you might find that it is becoming a bit root bound. If repotting is not possible, or not wanted, you can remove the plant and carefully prune the roots and just put a shallow extra layer of soil in the pot.