Oregano, a perennial herb, seasons spaghetti sauce and other Italian dishes. As a perennial plant, oregano grows back each year without needing to be replanted. To maximize its growth each year, it is wise to prune oregano plants near the end of the harvest season and before the first frost. Pruning throughout the summer can also result in fuller growth and a more plentiful harvest.
Cut back the stems of the oregano plant using pruning shears to a height of 2 or 3 inches about six weeks after planting. If the oregano plant is regrowing from the previous year, wait six to eight weeks after the plant's new growth begins in spring to prune it back. For large, woody oregano plants, prune the stems back to a length of 5 or 6 inches.
Deadhead ornamental oregano plants throughout the spring and summer to encourage the growth of new buds. The term "deadhead" simply refers to removing dead or wilted flowers from the plant to make room for new growth. To deadhead oregano, pinch or cut off the flower just below the bloom using your fingers or a pair of pruning shears.
Prune oregano plants at least twice throughout the harvest season. If the oregano plant gets plenty of sun and water, you may be able to harvest it every six to eight weeks. During dry or particularly hot summers, you may only need to prune your oregano once near the beginning of the season and once near the end.
Trim the roots of your oregano plant every few years to remove dead roots and to divide large plants. Replant the divided plants in separate containers with plenty of nutrient-rich potting soil.
Stop pruning your oregano plants in late August or early September. After pruning, new growth takes time to mature and if you prune your oregano plant too late in the season the new growth will not have time to mature before the first frost.
Cut your oregano plant down to the ground after the first frost. The plant will have gone dormant by this time and cutting the stems short will help to protect the plant during the winter.
Cover the remaining stub of the oregano plant with soil and, for added protection, spread a 5-inch layer of mulch over the soil.
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Pluck the oregano leaves from the stems you pruned and use them fresh or hang the stems upside down to dry. Pruning oregano is a good way to harvest the growth for your own use and is also important for the health of the plant. If you have an outdoor herb garden, pruning will also make room in your garden for the growth or addition of other plants. Trimming the roots and dividing oregano plants is especially important for potted specimens. Root trimming helps with the absorption of nutrients. Do not feel like the only time you can harvest your oregano is during pruning. Feel free to cut off a few sprigs throughout the summer if you need fresh oregano for a recipe.
Avoid any aggressive pruning or trimming of oregano plants during periods of particularly high heat. During the heat of summer, wait to trim the roots of oregano plants until the temperature cools in the fall and the plants fall dormant.