cool season · Brassicaceae
Growing Radish in Utah
Fastest crop in the garden — kid-proof and confidence-building. Succession every week.
Schedule (May 15 last frost)
When to do what
Direct sow
4/17
First harvest
5/15
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
Direct sow
Seed depth
0.5″
Plant spacing
1″
Row spacing
6″
Germination temp
45–85°F
Days to maturity
28 days
How we grow it
Step-by-step
- 1.
Direct sow 0.5″ deep, 1″ apart
Soil should be at least 45°F before sowing — black plastic mulch laid down two weeks ahead helps in our cool springs. Water in deeply.
- 2.
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.
- 3.
Harvest around day 28
Days-to-maturity is a rough guide — taste, color, and size are the real signals. Fastest crop in the garden — kid-proof and confidence-building. Succession every week.
From the farm
What we’ve learned growing radish
On our farm, radish 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
Radish 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) radish
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 (28 days from sowing) is a baseline. The real signals are color, size, and feel. Fastest crop in the garden — kid-proof and confidence-building. Succession every week.
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 radish. 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 radish
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:Radish seeds want exactly 0.5" of cover — about half an inch — about a fingernail deep. 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.
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 radish
+Can I direct-seed radish in Utah?
Yes. Direct sow, wait until soil temperature hits 45°F (use a soil probe thermometer; air temp is misleading). Sow 0.5" deep, 1" apart. Black plastic mulch laid 2 weeks ahead of sowing warms the soil 8-10°F faster.
+Why are my radish 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 radish survive a late frost in Utah?
Radish 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 radish take from seed to harvest?
28 days from direct sowing. 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 radish plants?
1" between plants in the row, 6" 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.