When to plant bok choy in Grand Rapids, Michigan
May 6 – May 20
Transplant outdoors · typical Grand Rapids yearClimate basis: NOAA station E Grand Rapids, MI (USC00202375), 3 mi (5 km) from downtown Grand Rapids (ZCTA 49503 centroid), elevation 746 ft, on the 1991–2020 climate normals. Transplant bok choy outdoors from approximately the dates above, anchored to the median last spring 32°F freeze (May 6). One year in ten still freezes after May 23.
The Grand Rapids year
- indoors under lights
- in the garden
- frost-free season
- 1-in-10 years still freeze to May 23
Every method, with its sources
Start seeds indoors
Apr 1 – Apr 15Maryland's pac-choi-scoped instruction to "start seeds indoors and plant 3 to 5-week old transplants into garden soil" supplies the 21–35 day seed-to-transplant lead, counted back from the start of the UNH-derived transplant window (day 0) as the registry's indoor-start policy requires, giving last spring frost minus 35 to minus 21 days; UNH's generic "four to six weeks" indoor period is not crop-specific and is not used. Anchored to the median last spring freeze (May 6). University of Maryland Extension · University of New Hampshire Cooperative Extension
Transplant outdoors
May 6 – May 20UNH Cooperative Extension states that Asian greens "like bok choi" bolt prematurely after cool exposure "so they should be set out after last frost" — a point rule, encoded per the registry window policy as the 14 days beginning at the last spring frost (0 to +14 days). Anchored to the median last spring freeze (May 6). University of New Hampshire Cooperative Extension
Direct-sow outdoors
Apr 8 – Apr 15University of Maryland Extension, on a page whose planting facts are explicitly scoped to "collards, kale, mustard, turnips, and pac choi", directs spring sowing "3 to 4 weeks prior to frost date", giving last spring frost minus 28 to minus 21 days; UNH's "set out after last frost" guidance for Asian greens governs setting out transplants and is encoded as the transplant window rather than treated as a competing sowing interval. Anchored to the median last spring freeze (May 6). University of Maryland Extension
Fall planting
Not calculatedNo fall window is encoded because Maryland's fall rule is a days-to-maturity calculation (time to maturity plus a 10–14 day "short day factor", counted back from the first fall frost) that yields a different offset for every cultivar across the 40–80 day maturity range Maryland states for these greens, while Minnesota Extension's fall guidance is fixed-calendar (direct seeding in July) rather than frost-anchored.
Variety assumption: Offsets assume leaf-harvested pac choi within the 40–80 day from-seed maturity range Maryland gives for this group of greens; both UNH and Minnesota Extension warn that this crop bolts after cold exposure or late spring frosts, so the pre-frost sowing window carries real bolting risk and the after-frost transplant window is the conservative option.
These windows describe typical years (1991–2020 climate normals), not this year's forecast. Freezes happen outside them — especially in frost pockets, valleys, and urban edges. Watch the forecast before committing tender plants.
Crop rule sources (2)
- University of Maryland Extension: Growing Leafy Greens in a Home Garden (accessed 2026-07-25)"Planting leafy green facts - collards, kale, mustard, turnips, and pac choi"
- University of New Hampshire Cooperative Extension: Cool Season Vegetables (accessed 2026-07-25)"Asian greens (like bok choi), and kohlrabi, are known to bolt prematurely if they are exposed to cooler temperatures, so they should be set out after last frost."