Field drying remains the primary bottleneck to consistent alfalfa haymaking under Korea’s humid, rain-prone summers. This study evaluated how dry matter (DM) yield and tedding frequency shape seasonal drying trajectories and leaf shatter in Cheonan during 2024. The experiment was conducted in May, June, August, September, and October 2024 with three DM yield levels (3, 5, and 7 ton/ha) and three tedding regimes (no tedding, once daily, and twice daily). Favorable May–June weather enabled swaths to reach <20% moisture within 100 h, whereas in September–October, moisture commonly remained ≥50%, indicating conditions unsuitable for dry hay. Yield effects on drying were generally small except in August, when re-wetting events accentuated between-group differences. Tedding effects were season-dependent: treatment differences emerged after rainfall in August and were evident in September, with twice-daily tedding producing the lowest moisture among tedding treatments. Leaf dropout rose with greater tedding frequency and higher DM yield; significant tedding effects were detected in June and September, and twice-daily tedding often exceeded no-tedding for leaf losses, particularly at 7 ton/ha. Collectively, omitting tedding is a viable option for May–June hay (4 days to ~20% moisture), while for post-June harvests, tedding offers limited drying benefits and may elevate leaf shatter; ensiling is therefore recommended when drying conditions are suboptimal.