cool season · Brassicaceae
Growing Bok Choi in Utah
Bolts in heat — strict spring + fall crop here. Baby bok choi at 30 days is the sweet spot.
Schedule (May 15 last frost)
When to do what
Start indoors
4/3
Transplant out
4/24
Direct sow
4/24
First harvest
6/5
Dates are calibrated for SUS Farms (Sevier County, Zone 6a, last frost May 15). For your own date, use the interactive calendar.
Planting
How deep, how far apart
Method
Indoor or direct
Seed depth
0.25″
Plant spacing
8″
Row spacing
12″
Germination temp
50–85°F
Days to maturity
45 days
How we grow it
Step-by-step
- 1.
Start indoors 6 weeks before last frost
Seed-starting mix in 2" or 4" cells. Bottom heat at 50–85°F until germination, then drop to room temperature. Light from a clip lamp 14–16 hours a day, 2" from the leaves.
- 2.
Harden off for 7 days before going outside
Day 1: 1 hour outside in shade. Add an hour and more sun each day. Skip the day if it’s windy or below 50°F. After day 7 the plants stay outside.
- 3.
Transplant 8″ apart in rows 12″ apart
Soil should be at least 50°F before transplanting — black plastic mulch laid down two weeks ahead helps in our cool springs. Water in deeply.
- 4.
Mulch and water consistently
2" of straw or wood chip mulch around the base. Drip line at the surface. Aim for 1" per week — including rain — measured at soil level, not by the calendar.
- 5.
Harvest around day 45
Days-to-maturity is a rough guide — taste, color, and size are the real signals. Bolts in heat — strict spring + fall crop here. Baby bok choi at 30 days is the sweet spot.
From the farm
What we’ve learned growing bok choi
On our farm, bok choi is one of the rotations that grounds the season. We test new varieties every year alongside the staples — usually one experiment per row, surrounded by what we know works. Failures here are how we know what to recommend; the success stories make it into the catalog and onto our table.
Pests & problems
Brassicaceae family pressures in Utah
Bok Choi shares its troubles with broccoli, cabbage, kale, radish, turnip, arugula. The pests and diseases below show up most years; the fixes are what we actually do, not what catalogs sell.
Scout weekly during the growing season — most outbreaks are 10x easier to manage when you catch them in week one.
Pest 1
Cabbage looper / imported cabbageworm — green caterpillars that lace-up brassica leaves. White butterflies are the adults; if you see them, eggs are coming. Bt spray is highly effective.
Pest 2
Flea beetles — tiny black beetles that pinprick leaves. Most damaging on young transplants. Floating row cover for the first 30 days of life.
Pest 3
Cabbage maggot — fly lays eggs at the base of stems. Brassica collars (cardboard rings around stems) prevent egg-laying.
Disease 1
Clubroot — gnarled, swollen roots; plant wilts. Soil-borne, persists 7+ years. Lime the soil to pH 7.0+ if confirmed; rotate Brassicas out for 7 years.
Disease 2
Black rot — yellow V-shaped lesions on leaf margins. Bacterial; spreads in wet conditions. Rotate, water at base, sterilize tools.
Companion planting
What to plant near (and away from) bok choi
Most companion-planting charts you see online are folklore. The pairings below have either USU Extension research, Cornell vegetable MD pages, or our own multi-year farm logs behind them.
Plant near
Good companions
- ✓Onions, garlic, chives (mask brassica scent from cabbage moths)
- ✓Dill (attracts beneficial wasps)
- ✓Sage (cabbage moth deterrent)
- ✓Beets (mineral exchange)
Plant away from
Bad companions
- ✗Strawberries (share fungal diseases)
- ✗Other brassicas in same bed sequentially (rotation rules)
Crop rotation
Brassicas in year 2 of a 4-year rotation. Best after legumes. Worst after other brassicas — disease carryover is severe.
Harvest & storage
Picking, keeping, preserving
When to pick
Days-to-maturity (45 days from transplant) is a baseline. The real signals are color, size, and feel. Bolts in heat — strict spring + fall crop here. Baby bok choi at 30 days is the sweet spot.
How to harvest
Clean cuts with sharp pruners or scissors heal faster than ripped stems and reduce disease entry points. Harvest early morning when sugars are highest and the plant is fully turgid; afternoon-harvested produce wilts faster. Don't harvest when leaves are wet — fungal spores ride along.
Short-term storage
Refrigerate at 32-40°F with high humidity (90%+). Most cool-season crops keep 1-3 weeks if cleaned and stored properly. Don't wash before storing — water on leaves accelerates spoilage.
Long-term preservation
Freezing, canning, drying, and fermenting all preserve bok choi. Pick the method that matches your kitchen and how you actually use the harvest — frozen tomatoes are great for sauce but bad for sandwiches; dried herbs work everywhere; fermented vegetables shine in salads.
Mistakes we’ve made
Common ways to fail at bok choi
Each of these has cost us a season at some point. Easier to learn from someone else’s lost crop than your own.
Planting too deep
The fix:Bok Choi seeds want exactly 0.25" of cover — about a quarter of an inch — about the diameter of a pencil. Deeper than that and the seedling exhausts itself before reaching light. Carrots and lettuce especially: shallow is right; sprinkle, then cover with a dusting of soil and tamp gently.
Skipping the harden-off step
The fix:Plants raised under indoor lights have soft cuticles and weak stems. Move them straight outside and they sunburn, snap in wind, or wilt and never recover. The 7-day gradual sun exposure is mandatory, not optional.
Watering on a calendar instead of by need
The fix:Stick a finger or screwdriver 4" into the bed. Damp at depth = wait. Dry at depth = water deeply. Calendar watering ignores rain, heat waves, and seasonal evapotranspiration — leading to either drought stress or root rot.
Ignoring soil pH
The fix:Most Utah backyard soil tests at pH 7.4-8.4 (alkaline). Iron and zinc become unavailable to roots above pH 7.5 — leaves yellow, growth stalls. A $20 mailer test from USU Extension tells you exactly what your soil needs. Sulfur amendment in fall, foliar iron mid-season as needed.
Letting heat-bolt happen mid-season
The fix:Cool-season crops bolt (go to seed, become bitter) when night temps stay above 70°F. Plant for an early-spring AND late-summer harvest, with a heat gap in between. Fall plantings of lettuce, spinach, and brassicas are often better than spring ones in Utah.
Common questions
Frequently asked about bok choi
+When should I start bok choi indoors in Utah?
In Sevier County (last frost May 15), start 6 weeks before — that's roughly April. If you're at higher elevation (Park City, Logan), add 2 weeks. Lower elevation (Salt Lake, St. George), subtract 2-4 weeks. Use the interactive seed-starting calendar at /seeds/calendar to dial it in for your specific frost date.
+Can I direct-seed bok choi in Utah?
Yes — many growers do, especially in our short season. When direct sowing, wait until soil temperature hits 50°F (use a soil probe thermometer; air temp is misleading). Sow 0.25" deep, 8" apart. Black plastic mulch laid 2 weeks ahead of sowing warms the soil 8-10°F faster.
+Why are my bok choi leaves turning yellow?
Three usual suspects. (1) Iron chlorosis — yellow leaves with green veins is the Utah classic; the cause is alkaline soil locking up iron. Foliar iron rescues the season; sulfur amendment in fall fixes it long-term. (2) Nitrogen deficiency — entire leaf yellow including veins, starts with old leaves. Side-dress with compost or a slow-release organic fertilizer. (3) Overwatering — yellowing accompanied by soft, mushy stems means the roots are drowning. Check drainage; reduce water frequency.
+Will bok choi survive a late frost in Utah?
Bok Choi is a cool-season crop and tolerates light frost (down to ~28°F) once established. Tender seedlings just out of the greenhouse are more vulnerable — cover with floating row cover when overnight forecasts show below 35°F. After hardening off properly, mature plants of this family typically shrug off late-spring frosts that would kill warm-season crops.
+How long does bok choi take from seed to harvest?
45 days from transplant. Add 42 days for the indoor seed-starting phase, so total time from sowing seed to first harvest is roughly 87 days. Days-to-maturity is a baseline — cool springs add a week or two; hot summers can speed up by similar amounts. Use it for planning, not as a strict calendar.
+What's the spacing between bok choi plants?
8" between plants in the row, 12" between rows. That gives mature plants room to fill in without competing. Closer spacing reduces yield per plant; wider spacing wastes garden space. The numbers come from average mature plant size at full vegetative growth — adjust slightly for compact varieties (closer) or large heirlooms (wider).
Same family (Brassicaceae)
Related crops
Sources:Johnny’s Selected Seeds·USU Extension·Cross-checked with our greenhouse logs.