Question: how do you know when your spring onions are ready to harvest?
Answer: When to harvest spring onions It takes about 8 weeks for spring onions to mature. Your onions will be ready for harvest when they reach a height of 6 inches and a thickness of about 1/2 inch. If you allow the spring onions to grow longer, don't let them get larger than 1 inch, or the flavor will be very weak.