Purging the canning jar of oxygen by blowing in carbon dioxide from a kegging system will also help prolong freshness. It's common to get 4 or 5 harvests per year by picking the biggest, most mature hops every two weeks or so as the flowers ripen. Patience and judgement are important since cones left on the vine too long turn brown and are obviously oxidized and spoiled, while immature hops have little lupulin in them. At the end of the growing season when the leaves have fallen or turned brown, cut the vines at the surface of the soil and if possible remove the twine. After cutting back the vines a layer of three or four inches of mulch and composted manure can be put over the exposed vines for insulation and nutrition during the winter.
Japanese beetles are the number one nuisance in many areas.
Certain plants such as rose bushes may also attract the beetles, so it's best to keep those plants away from your hops. Also, the beetles' larvae live in the ground, and in cases of extreme Japanese Beetle infestation the surrounding lawn may need to be treated accordingly. A number of other pests, such as aphids, can harm hops, and can be treated with any number of pesticides. As with any consumable, you should ensure that any pesticide is well washed off before using the hops. One other hazard is animals.