Learning how to cut asparagus is all about timing. Asparagus should be cut only during the first six to eight weeks of growth. After that, you run the risk of damaging the plant because, in order for the plant to grow a healthy root system, the plant requires a several months of undisturbed growing time.
Within a few weeks after you have finished harvesting, the spears that are left undisturbed will grow into airy plants about five or six feet tall that resemble bushes. During the remainder of the summer, the asparagus plants will continue to strengthen their root system, which is very important for continued harvests.
Also, while the spear of the plant is extremely tender, the stalk becomes more woody or fibrous the further down the stalk you travel. Finally, the color runs from white to green to a slight purple color. While not all spears will have the purple color on them, if they do, it's perfectly fine. The further down the plant you travel, however, you'll begin to notice several shades of green, starting with dark green, then lighter green, pale green and finally white.
Do not pick spears that have begun to unfurl, as the stalk will already be too woody and the delicate taste asparagus is known for will already have disappeared.
When you harvest asparagus, you may want to use a specialized knife called an asparagus knife. The asparagus knife has a curved blade and allows you to cut one individual asparagus spear at a time without damaging other spears. You can also use a regular flat blade knife.
Flat Blade Versus Asparagus Blade: The only problem with a flat blade knife is that it's easier to damage nearby spears. Because folklore dictates that asparagus spears be cut about one inch below the soil, it is impossible to see if there is another spear nearby that is about to emerge. Any additional emerging spears are more readily missed if you use an asparagus knife because the asparagus knife is curved with the blade on the inside of the curve. Theoretically, the spear you want to cut is the only spear that is touched when you use an asparagus knife. The reason asparagus spears are supposed to be cut beneath soil level is that gardening lore says this will prevent infection or bacteria from entering the cut spear and causing damage to the entire plant. However, new evidence suggests that asparagus spears that are cut above ground will simply dry up and whither away without causing problems to the plant.
Cut Asparagus in Uniform Lengths and Thicknesses: Cut spears that are about the same diameter and about the same height. A good call is to choose asparagus stalks that are about one half inch in diameter and about six to eight inches in height. Taller spears will have already become too woody. For a pretty plate, leave the spears intact. You can also cut the spears into even lengths by laying them side by side on a plate and cutting the whole bunch at once into about four one to one and one half inch pieces.
Harvest Daily: Once you have harvested the asparagus-a task that should be done every day or at least every other day during season-wash the asparagus, and separate the spears into like bunches, using diameter as the guide. Asparagus is a tender vegetable and doesn't require a lot of cooking time. To make sure all spears cook evenly, use spears that are identical in size.
Use a paring knife, and work your way up the spear from the bottom by pressing the sharp blade against the side of the spear, slightly cutting into the spear. Keep moving up the spear until the knife easily cuts into the stalk. At that point, cut off the bottom of the stalk, and discard it. What you will have left is a spear about five to seven inches in length that starts out as light green and then turns green and finally either very dark green or slightly purple at the tip. Because the two to three inches at the bottom of the spear, or the light green area of the spear, will also be a little tough, it's advisable to pare off the peeling at this point. Use a downward motion, and peel the asparagus all the way around the bottom of the stalk.
The end result will be a spear of asparagus that will look very similar to the spear you originally picked. The color will be nearly white or very light green at the bottom and build all the way to the deep green or purplish spear at the top. Steam for about two to three minutes, and serve hot with a dab of butter. Peeling the stalk means every spear of asparagus will be as tender at the bottom as it is at the top.