Cucumbers are generally ready for harvest between 50 to 70 days after planting, depending on the variety. The best time to pick cucumbers is when they reach the appropriate size for their type and are still firm and green without any yellowing, which indicates overripeness and bitterness. Key points for harvesting cucumbers:

• Harvest about 8 to 10 days after the first female flowers open.
• Slicing cucumbers are typically harvested at 6 to 8 inches long.
• Pickling cucumbers should be harvested smaller, around 1.5 to 4 inches depending on the intended use (e.g., gherkins are picked at about 1.5 to 2 inches).
• Cucumbers should be firm with a deep green skin; avoid cucumbers with yellow skin as they tend to be bitter.
• Harvest in the cool morning hours for peak crispness.
• Cut cucumbers from the vine with a small piece of stem attached to prevent rot; avoid pulling or twisting to protect the vines.
• Frequent picking is important as cucumbers ripen at different times and can become bitter if left on the vine too long.

To summarize, monitor your cucumber plants closely around 50 days after planting and harvest cucumbers while they are firm, green, and at the right size depending on their variety and use. Harvest regularly to maintain quality and encourage more production.