You are a gardening and email marketing expert. Write a detailed, 2400-word guide on email for greenhouses. The guide must cover: 1) Building an email list of gardeners, 2) Welcome sequences for new subscribers, 3) Seasonal plant availability emails, 4) Gardening tips and advice, 5) Event and workshop announcements, 6) Customer appreciation and loyalty, 7) Referral and friend campaigns, 8) Re-engagement for inactive subscribers, 9) Metrics for nurseries (sales), 10) Visual storytelling with plants.