真正要紧的四个日期
| 日期 | 什么时候 | 意味着什么 |
|---|---|---|
| 春季终霜 (50%) | — | 有一半的年份会在这个日期之后还结霜。这是平均值,不是保证。 |
| 春季终霜 (10%) | — | 只有十年里的一年会在这之后结霜。凡是不能重种的作物,就按这个日期来。 |
| 秋季初霜 (50%) | — | 有一半的年份会在这个日期之前结霜。秋菜就是从这里往回推算的。 |
| 秋季初霜 (10%) | — | 早霜年份。如果某种作物必须收成,就争取在这之前收。 |
这些数字从哪儿来
Sunrise 城内没有长期记录的气象站,所以这里的霜冻日期是 模型推算的,不是实测的。它来自一张半度分辨率的气候网格:把 6,808 个 NOAA 站点(1991–2020 常态值)的 结霜日期与地形、2023 年 USDA 耐寒栅格拟合之后,再读取你所在城市落在的那个网格。拿这些站点本身做校验, 该模型平均误差大约在一周以内——分区与站点完全吻合的比例为 67%,相差不超过半个分区的比例为 97%。 一个网格大约覆盖 35 × 28 英里,所以这是一个“街区级”的答案,不是“后院级”的。如果你附近有 有气象站支撑的地点, 优先用那一个。
这些数据到底有多准?
Extension recommendations for the same crop routinely disagree by two to four weeks, and occasionally more, so these offsets should be presented as windows and starting points rather than deadlines. Three things drive the spread. (1) Regional risk tolerance: for warm-season crops, Colorado State and Utah State put tomatoes, peppers and melons out about 14 days after the last frost, while University of Missouri's calendar works out to roughly 25-35 days after the last frost and University of Maryland's window runs from the frost date itself out to 45 days past it. That is a real 6-week spread for the single most popular garden crop, and it exists because a short-season mountain state is optimizing against a short season while a humid continental state is optimizing against cold, wet spring soil. (2) Soil temperature versus calendar date: most Extension services now say the honest trigger is soil temperature at 4 inches, not the frost date, and the frost-relative number is a convenience translation. A cold, wet spring can push the real date two or three weeks past the calendar recommendation. (3) Days-to-maturity is variety-specific and is measured differently for direct-seeded versus transplanted crops - seed catalogs count from transplant date for tomatoes, peppers, eggplant and cole crops, but from sowing for roots and greens - so a 'days to maturity' range of 60-85 for tomato is genuinely 60-85 depending on which packet you bought. Additionally, the average last frost is a 50% probability, meaning half of all years have a frost after that date; Extension services commonly advise waiting 1-2 weeks past it for anything frost-tender, or being prepared to cover. Treat every number here as plus or minus about 10-14 days.
关于气象站本身:一个气象站只是一个点。城市会蓄热,山谷会积冷空气, 朝北坡地上的菜园可能比一英里外的晚上两周。把这一页当成起点,让你自己的菜园去修正它—— App 里的日记正是为此而设。
附近的地点
Sunrise 的播种提醒
每逢新月和满月发一封短信,告诉你 Sunrise 现在正好在哪些作物的种植窗口里——依据本页的霜冻日期算出。免费,一键退订。
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想在菜园里用手机看?Moon Phase Garden 把你的霜冻日期、种植时间窗和今晚的月相放在一处, 离线也能用,还能让你用自家菜园的实际情况覆盖这些日期。免费,无广告。