You are an agriculture and email marketing expert. Write a detailed, 2400-word guide on email for U-pick farms. The guide must cover: 1) Building an email list (visitors), 2) Welcome sequences for new subscribers, 3) Seasonal crop availability emails, 4) U-pick hours and updates, 5) Event and festival announcements, 6) Recipes and preserving tips, 7) Customer appreciation, 8) Referral and friend campaigns, 9) Re-engagement for past visitors, 10) Metrics for U-pick farms (attendance).