Buy the 2015 Old Farmer's Almanac!
In general, harvest the outerIn general, harvest the outer leaves to allow the inner ones to develop further. However, if the plant develops a large stalk with buds/flowers/seeds (called bolting), then you should pull the entire plant and use the leaves as you can. The leaves on the stalk will look narrower. When a spinach plant starts to bolt, it makes the leaves bitter. You can try to slow the bolting by pinching off the flower/seedheads as they appear, or keeping the plant moist and providing a little shade if the weather gets too warm.   Bolting can be caused by stress, warm temperatures, or daylight longer than about 14 hours (which happens in many areas of the US around May). Because of this, spinach is best planted in early spring or fall, when it is cooler and the days are shorter.

2015 Garden Calendar2015 Weather Watcher's Calendar2015 Recipes Calendar2015 Engagement Calendar 2015 Everyday Calendar2015 Country CalendarNew Year Cross StitchLobster Rope Doormats