Harvesting asparagus is Final step if you follow my article before. If you’ve done everything right, you can expect to reap the benefit of full, firm, hardy spears during the springtime of your asparagus’ third year. These older plants should be able to give you 4-8 weeks of good spears over 1/2 inches in diameter and larger. For home harvesting, simply snap off the spear as close to the ground as you can.
Cutting asparagus spears with a knife is not that important, and it really doesn’t help too much with the yield size. Avoid cutting with a knife below soil level if you don’t know where the crown is located. Once the asparagus spears are 3/8 inches, stop harvesting, fertilize appropriately (see above) and let your plants start to grow their beautiful foliage for the next season’s crop.
You can harvest some spears the second year, but be careful not to harvest for too long (no more than 4 weeks). If the spears are smaller than 3/8 inches round, stop harvesting. The best time to harvest asparagus is when spears are 4 to 10 inches tall. If your spears are tough or the heads are not tight and have begun leafing out, they have grown too tall and old for harvesting. In some areas, you might have to harvest every day to prevent the spears from getting woody or fibrous. If spears become fibrous and you are not near the end of your harvesting season, cut them off and let new spears grow in their place. You could also just leave these spears to develop and cut others that grow around them. The idea is that the developing spear may help feed other spears and increase the harvest. Allowing the foliage to grow may also cause future spears to get tough faster or just stop as many from coming up. You will have to try it out for yourself to see which idea works.
Inadequate spears can indicate underlying problems. Thin spears can be a sign of over-harvesting or lack of fertility. Tough spears can be a sign that your plants are not getting enough nutrition or water, or that the beds need to be renovated (more mulch, slow release/organic fertilizer, compost, etc.)