warm season · Geraniaceae
Growing Geranium in Utah
The hanging-basket workhorse. Pelargonium, technically. Deadhead for continuous bloom all summer.
Schedule (May 15 last frost)
When to do what
Start indoors
3/6
Transplant out
5/22
First harvest
8/21
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
Start indoors
Seed depth
0.0625″
Plant spacing
12″
Row spacing
18″
Germination temp
70–80°F
Days to maturity
90 days
How we grow it
Step-by-step
- 1.
Start indoors 10 weeks before last frost
Seed-starting mix in 2" or 4" cells. Bottom heat at 70–80°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 70°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 90
Days-to-maturity is a rough guide — taste, color, and size are the real signals. The hanging-basket workhorse. Pelargonium, technically. Deadhead for continuous bloom all summer.
From the farm
What we’ve learned growing geranium
Geranium earns its space in the garden because pollinators don't care about your tomato yield unless something invites them in. Plus, geranium pairs surprisingly well with vegetable beds — interplanted strategically, it acts as a trap crop, a pollinator beacon, or just a reason to walk the rows in July when the work is most relentless.
Pests & problems
Geraniaceae family pressures in Utah
Geranium shares its troubles with geranium, pelargonium. 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
Whitefly (greenhouse problem) — sticky honeydew on leaves; clouds of tiny whites when disturbed. Yellow sticky cards; horticultural soap.
Disease 1
Botrytis (gray mold) on flowers in cool damp weather. Remove spent blooms; improve airflow.
Companion planting
What to plant near (and away from) geranium
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
- ✓Roses (deter Japanese beetles)
- ✓Container plantings with petunias and verbena.
Plant away from
Bad companions
- ✗Nothing significant.
Crop rotation
Containers are best refreshed every season — toss the old soil and start fresh.
Harvest & storage
Picking, keeping, preserving
Cut flowers
Cut in early morning when stems are turgid. Strip lower leaves, plunge into clean water immediately. Recut stems at a 45° angle once inside, ideally underwater. Change vase water every 2-3 days for longest vase life.
Drying
Hang small bundles upside down in a dark, dry, ventilated space. 2-3 weeks. Best for everlasting flowers (statice, strawflower) and seed heads. Most fresh-cut flowers don't dry well — they crumple instead of preserving form.
Mistakes we’ve made
Common ways to fail at geranium
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:Geranium seeds want exactly 0.0625" 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.
Planting too early
The fix:A warm-season crop set out before soil hits 60°F at 4" depth sits and sulks — sometimes for weeks before either dying outright or refusing to grow until July. Wait. Better to plant a week late than plant 3 weeks early into cold soil.
Common questions
Frequently asked about geranium
+When should I start geranium indoors in Utah?
In Sevier County (last frost May 15), start 10 weeks before — that's roughly March. 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.
+Why are my geranium 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.
+Can I plant geranium before the last frost date?
Not safely. Geranium is a warm-season crop — even a light frost (28-32°F) kills the plant or stunts it for the rest of the season. Wait until soil hits 70°F at 4" depth AND there are no freezing temperatures in the 14-day forecast. In Sevier County that's typically the third week of May. Black plastic mulch + floating row cover let you push planting 7-10 days earlier.
+How long does geranium take from seed to harvest?
90 days from transplant. Add 70 days for the indoor seed-starting phase, so total time from sowing seed to first harvest is roughly 160 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 geranium 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).
Sources:Johnny’s Selected Seeds·USU Extension·Cross-checked with our greenhouse logs.