Summarize this article in one sentence.
The overall size of your chives will vary depending on the variety you grow, but all varieties are harvestable around 710 inches (17.825.4cm). This normally occurs around mid summer, and will continue until the weather cools below freezing. In some areas with light winters, chives will remain evergreen and produce harvestable plants until the following year. Use a pair of gardening shears or scissors to cut your chives straight across, starting from the outside of the plant and working in. Cut the chives about 2-inches from the base of the plant, as this will stimulate new growth for additional harvests. Do not harvest the entire plant at one time; cutting all of the leaves off will stop future growth. Try not to cut them at an angle, as this will cause them to lose moisture more rapidly than if they are cut straight across. This is because cutting at an angle exposes more of the stem, and therefore moisture in the plant dissipates more quickly. For the best-tasting crop, harvest your chives during the summer and late fall 3 to 4 times total during the year. It is not necessary to harvest the entire plant at once; only cut what you need from a patch, and harvest that particular patch 3-4 times per year. Chives can become an invasive species, as they are self-seeding and pollinating and may take over your garden. To prevent this, cut off the flower heads at harvesting time. This will prevent the flowers from seeding and spreading to other areas of your garden. Continue deadheading the flowers at each harvest. As a form of pruning, cutting off all the chives in the late fall will help to produce a better crop the following summer. Use your gardening shears to cut off the top of the entire chive plant 12 inches (2.55.1cm) from the base. This should be done around the months of October or November. Chives are perennial plants, so they will continue to grow back on their own so long as they are taken care of. As a result of continually growing for many years, chives can get quite large. To prevent the chives from overtaking your garden and becoming unruly, it is practice to divide the chive plants every few years. Chives are a type of bulb, so they are easy to divide. Simply dig down in the dirt to reach the bulb, and split each large plant into sections the original size for replanting. Give the extra sections to friends and neighbors to start their own herb garden, or add them to your compost. Consider replanting chive your spare chives at the base of your apple trees. The chive plants will prevent a type of disease called 'apple scab' from occurring on the trees. Chives are said to repel deer, so consider planting your spare divisions in an area that deer have been a problem for you.

Summary:
Wait to harvest your chives when they are at least 7 to 10 inches (17.8 to 25.4cm) in height. Cut chives 2-inches from the base. Harvest your chives 3-4 times per year. Deadhead the flowers when they start to seed. Cut off all the chives at the end of the growing season. Divide chive plants every 3 to 4 years.