cool season · Asteraceae
Growing Iceberg Lettuce in Utah
Crisphead — needs 60-day cool window. Spring crop only at our elevation; bolts in July heat.
Schedule (May 15 last frost)
When to do what
Start indoors
4/3
Transplant out
4/24
Direct sow
4/17
First harvest
7/3
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
0.125″
Plant spacing
12″
Row spacing
18″
Germination temp
40–75°F
Days to maturity
70 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 40–75°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 12″ apart in rows 18″ apart
Soil should be at least 40°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 70
Days-to-maturity is a rough guide — taste, color, and size are the real signals. Crisphead — needs 60-day cool window. Spring crop only at our elevation; bolts in July heat.
From the farm
What we’ve learned growing iceberg lettuce
On our farm, iceberg lettuce 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
Asteraceae family pressures in Utah
Iceberg Lettuce shares its troubles with lettuce, sunflower, zinnia, marigold, calendula, cosmos, dahlia. 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
Aphids — colonies on undersides of new growth. Beneficial insects (lacewings, ladybugs) handle most outbreaks if you stop spraying broad-spectrum insecticides.
Pest 2
Slugs (lettuce especially) — rasped holes in leaves overnight. Diatomaceous earth, beer traps, or copper tape around bed edges.
Pest 3
Earwigs — pinch holes in flower petals at night. Roll up newspaper, leave overnight, dump in soapy water in the morning.
Disease 1
Powdery mildew — late-summer issue. Most common on zinnias; pick resistant cultivars (Profusion series).
Disease 2
Lettuce drop (Sclerotinia) — sudden wilting at the base. Improve drainage, mulch shallowly, rotate every 3 years.
Companion planting
What to plant near (and away from) iceberg lettuce
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
- ✓Tall flowers (zinnias, sunflowers) shade lettuce in summer to delay bolting
- ✓Carrots (no competition)
- ✓Onions (pest deterrent)
Plant away from
Bad companions
- ✗Beans (lettuce can stunt bean germination)
- ✗Dense plantings without airflow (mildew)
Crop rotation
Less critical than for Solanaceae or Brassicas — Asteraceae are mostly pest-light. Still good practice to move 2-3 years.
Harvest & storage
Picking, keeping, preserving
When to pick
Days-to-maturity (70 days from transplant) is a baseline. The real signals are color, size, and feel. Crisphead — needs 60-day cool window. Spring crop only at our elevation; bolts in July heat.
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 iceberg lettuce. 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 iceberg lettuce
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:Iceberg Lettuce seeds want exactly 0.125" of cover — about barely covered with a sprinkle of fine soil. 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 iceberg lettuce
+When should I start iceberg lettuce 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 iceberg lettuce in Utah?
Yes — many growers do, especially in our short season. When direct sowing, wait until soil temperature hits 40°F (use a soil probe thermometer; air temp is misleading). Sow 0.125" deep, 12" apart. Black plastic mulch laid 2 weeks ahead of sowing warms the soil 8-10°F faster.
+Why are my iceberg lettuce 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 iceberg lettuce survive a late frost in Utah?
Iceberg Lettuce 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 iceberg lettuce take from seed to harvest?
70 days from transplant. Add 42 days for the indoor seed-starting phase, so total time from sowing seed to first harvest is roughly 112 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 iceberg lettuce plants?
12" between plants in the row, 18" 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 (Asteraceae)
Related crops
Sources:Johnny’s Selected Seeds·USU Extension·Cross-checked with our greenhouse logs.