Deadheading is cutting off flowers as they wither or don’t look as good. Old blooms left on the plant may have been pollinated and may begin to form seed pods (hips). The formation of hips requires a lot of energy from the plant and slows flower production. By preventing the formation of hips, deadheading encourages the rose bush to grow new flowers.
The choice of which spot to deadhead at is influenced by what shape you want the bush to take, and which direction you want a particular cane to grow. Usually, you will want to cut the stem at a 45‑degree angle just above an outward‑facing leaf. Make sure the high side of the cut is the side the leaf set is on.
To deadhead, remove the flower by making a diagonal cut just above the next 5 or 7‑leaf branch down on the stem. The idea is to cut to a bud eye capable of producing a healthy cane. If this would cause too much of the cane to be removed, a 3‑leaf branch can be chosen instead. The first year cut back to the first 3 or 5‑leaf branch. In following years cut far enough down to get to a 5‑leaf branch with a leaf bud that is facing outward. This will open up the plant.
Once blooming roses do not need to be dead headed. They bloom once and then they are finished blooming for the year. However, once‑blooming roses may be (in fact, should be) pruned after they are finished blooming. They should NOT be pruned in the fall or before they bloom because they bloom on the previous year’s growth.
Stop deadheading as of September 1 in zones 4 and 5. It is a good practice to let the last roses on HT’s produce hips because it makes them more frost hardy. It causes the plant to undergo chemical changes that slow down growth, inhibit blooming and generally prepare for dormancy by focusing its energy on ‘hardening’ the canes. The formation of hips tells the plant that it’s “done its job” and can now rest from its labors.