Geraniums in Zone 6: The May Planting Window, Which Varieties Overwinter, and How to Keep Them for Years

Walk through any zone 6 garden center in March and you’ll find benches loaded with geraniums — often weeks before it’s safe to plant them. Buy transplants then, set them out that weekend, and most will stall for three weeks while cold nights shut down root activity. The plants aren’t the problem. The timing is.

Pelargoniums (the tender South African natives sold universally as geraniums) need nighttime temperatures consistently above 50°F to establish and grow. In zone 6 — covering Pittsburgh, Columbus, Kansas City, and Chicago — that window opens in early to mid-May, not when retailers put them on display. This guide gives you the exact planting calendar for both zone 6a and 6b, a breakdown of which of the four geranium types holds up through the full season, and a genuine decision framework for overwintering so you’re not making the same guess every September. For general Pelargonium care fundamentals, see our complete Geranium Care Guide.

The Zone 6 Planting Calendar

Zone 6 is split into Zone 6a (average minimum winter temperature -10°F to -5°F) and Zone 6b (-5°F to 0°F), with last spring frosts typically arriving between late March and late April depending on your location. But the last frost date and the safe planting date for geraniums are two different numbers.

Pelargoniums experience root stall when soil temperatures drop below 50°F, and chilling injury sets in on nights below 40°F — even without a visible freeze. Planting at your last frost date means setting plants into still-cold soil where they’ll sit motionless for two to three weeks, burning through energy reserves without growing. Waiting a few extra weeks costs nothing and gains you plants that actually establish quickly.

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Iowa State University Extension recommends waiting until mid-to-late May in Iowa’s zone 5–6 regions before planting annual geraniums outdoors — a conservative target that works as the safe upper bound for zone 6a as well. [2] If you want a simple rule: May 1 is your go-date for zone 6b, May 10 for zone 6a.

Starting from seed? Count 12–16 weeks back from your safe planting date. Zone 6b gardeners should start seeds indoors in mid-to-late January; zone 6a in early February. Most zone 6 gardeners skip this and buy transplants in late April or early May — a perfectly reasonable choice that cuts the effort without sacrificing summer color.

Bought transplants early? Garden centers in zone 6 stock geraniums from March onward. If you buy early, keep transplants on a bright indoor windowsill or a protected porch above 45°F until your safe planting date. Don’t leave them on an unheated deck overnight when temperatures are still dipping into the 40s.

Which Geranium Type Suits Zone 6?

Not all plants sold as geraniums perform equally through zone 6’s five-month growing season. The four types you’ll find at nurseries have meaningfully different heat tolerances — choosing the right one for your goal saves real disappointment, especially with Martha Washington types in summer.

Zonal geraniums are the zone 6 workhorse. Named for the darker banded marking across the leaf, they produce continuous blooms from late May through the first hard frost, handle July heat without shutting down, and tolerate dry spells better than other types. The Maverick, Patriot, and Calliope series were bred for extended outdoor performance in exactly these conditions. For beds, borders, and containers in zone 6, zonal is the reliable default.

Ivy geraniums (P. peltatum) trail and cascade beautifully in hanging baskets and window boxes. They bloom well, but prefer morning sun over all-day exposure — afternoon shade in zone 6’s peak-summer heat keeps them performing longer and significantly reduces how often you need to water. In full sun from June through August, ivy types need watering almost daily in hot weather.

Martha Washington warning for zone 6 gardeners: Regal pelargoniums evolved in southern Africa’s cooler highland regions and stop producing blooms reliably once temperatures consistently exceed 80°F. In zone 6, that happens by mid-June to early July. Martha Washington geraniums are genuinely spectacular in May and early June, but they’re a cool-season spring plant, not an all-summer annual. If you expect non-stop color from May through October, choose zonal or ivy types instead. [1]

Scented geraniums are heat-tolerant and grown primarily for fragrant foliage — lemon, rose, peppermint, and nutmeg varieties all handle zone 6 summers without issue. Their flower display is modest, but they’re excellent in herb gardens or as texture accents in container arrangements.

Soil, Sun, Watering, and Fertilizing

Sun: Geraniums require a minimum of 6 hours of direct sunlight daily for reliable blooming — fewer than 6 hours produces leggy stems and sparse flowers. [1] In zone 6 locations that regularly hit 90°F in August, afternoon shade helps ivy geraniums and prevents containers from drying out too fast; zonal types handle full sun without issue through zone 6 summers.

Soil pH matters more than most guides admit: Pelargoniums perform best in soil with a pH between 6.0 and 6.6. Below 6.0, they absorb excessive iron and manganese, causing leaf spotting and tip burn that’s easily misread as a pest problem or disease. If your plants show persistent spotting despite proper watering and adequate light, check soil pH before reaching for a fungicide.

Fertilizing: Before planting, work 1 to 2 pounds of a balanced fertilizer such as 10-10-10 per 100 square feet into the planting bed. [2] For container plants, use a dilute water-soluble fertilizer every 2 to 4 weeks through the season. Once plants are actively blooming in June, switching to a fertilizer higher in potassium — the third number in the N-P-K ratio — promotes more flower development than a balanced formula. High nitrogen pushes leafy growth; potassium supports the carbohydrate movement and cell development that drive flower bud formation. Look for ratios like 5-10-15 or any “bloom booster” formula with a high third number.

Watering: In-ground geraniums need about 1 inch of water per week during dry periods. [2] Container plants dry out much faster — in zone 6’s hot July and August, potted geraniums may need water two or three times a week. Test by pressing your finger 1 inch into the soil; water when it’s dry at that depth. Always water at the base of the plant, not over the foliage — wet leaves in warm conditions invite Botrytis gray mold. [1]

Zone 6 Seasonal Care Calendar

April: If you’ve purchased transplants early, keep them indoors or on a protected porch above 45°F. Begin hardening off in mid-to-late April — move plants outside for 1 to 2 hours in indirect light and increase daily exposure over 7 to 10 days before leaving them out overnight.

Early to mid-May (plant-out): Set transplants into warm soil after your zone 6 safe planting date. Water in with dilute fertilizer. Pinch any leggy stems back by a third to encourage bushy, branching growth.

Late May through June: First major bloom flush. Deadhead weekly — remove the entire spent flower stem down to the next leaf node, not just the petals. Geraniums produce flowers in clusters called umbels; once the last bloom in a cluster fades, the whole stem should come off. Regular deadheading prevents the plant from redirecting energy toward seed production and keeps the bloom cycle running continuously through summer.

July through August: Peak heat. Container plants may need water every 2 to 3 days. Continue deadheading. Pinch overly long or bare stems in early July to encourage new growth for the fall bloom push. Switch to a high-potassium fertilizer if you haven’t already.

September: Reduce fertilizing as growth slows. Zonal geraniums often produce their second strong bloom flush as temperatures cool below 80°F. If you’re using the cutting method to overwinter, take cuttings by mid-September — they need 6 to 8 weeks to root before you want them settled for winter.

October: Bring plants indoors or begin overwintering preparation before the first hard frost. Zone 6a first frosts typically arrive between October 15 and October 25; zone 6b between October 20 and November 1. A single hard freeze kills pelargoniums — don’t wait for the forecast to be certain.

Overwintering: Three Methods and How to Choose

Geraniums in zone 6 die at the first hard frost. Your options are to overwinter them, replace them each spring, or do some of each. No single method is universally better — the right choice depends on how many plants you have, what storage space is available, and whether the savings justify the effort.

When buying new plants each spring makes more sense: You have five or fewer plants. Quality transplants at your local nursery cost $4–8 each. You enjoy choosing new varieties and colors each season. You have no suitable cool storage space. The math favors replacement.

When overwintering pays off: You have more than eight plants. You grow collector varieties or unusual colors that aren’t easy to find. You have an unheated basement or garage that stays between 45°F and 55°F. You want larger, more established plants ready earlier in May.

Method 1 — Indoor Houseplant

Before the first hard frost, dig bedding plants or move container plants. Cut back by one-third to one-half to reduce water loss through leaves. [3] Place in your sunniest window — south-facing is ideal — or add a simple grow light. Maintain daytime temperatures around 65°F to 70°F and nights around 60°F to 65°F. [2] Water only when the top inch of soil is dry. The main cause of winter losses indoors is overwatering in low-light conditions — plants use very little water when not in active growth. Pinch back any leggy growth in January or February to encourage branching before spring.

Best for: Prized specimen plants, gardeners with good south-facing window space, anyone who wants the largest possible plants for early May planting.

Method 2 — Bare-Root Storage

Dig plants before the first hard frost. Gently shake or rinse most soil from the roots. Store in a paper bag — top folded but not sealed — in a cool, dark location that stays between 45°F and 55°F. An unheated basement or interior garage space in zone 6 usually qualifies. [3] Leaves will yellow and drop during storage; this is normal dormancy. Check plants monthly and soak the roots briefly in water if they look very dry and brittle, then return to storage.

In mid-March, remove from storage and cut back to firm, green live tissue. [4] Pot up in fresh compost and move to a bright indoor location until May. Expect 10 to 20% of plants not to revive — bare-root attrition is normal, especially with older or large plants.

Best for: Multiple plants with limited indoor light space, anyone with a reliably cool (but not frozen) unheated garage or basement.

Method 3 — Cuttings

Take 3 to 4 inch terminal cuttings in late August or early September — this leaves enough time for the 6 to 8 weeks of rooting before you want compact plants settled for winter. [3] Remove lower leaves, dip the cut end in rooting hormone, and insert into perlite, vermiculite, or a sand-peat mix. Keep the medium moist in bright indirect light; avoid direct sun during rooting. Transfer rooted cuttings to 3-inch pots when established. This method also lets you multiply stock — start cuttings from one parent plant and discard the woody original.

For a detailed step-by-step on taking and rooting cuttings, see our geranium propagation guide.

Best for: Expanding your collection, ivy geraniums (which are difficult to store bare-root), or when the parent plant has become old and woody.

Hardening Off After Overwintering

Plants that have spent winter indoors — whether as houseplants, potted-up bare-root revivals, or rooted cuttings — need a 7 to 10 day reacclimation before going into zone 6 beds or outdoor containers. Moving them directly from a 65°F windowsill to full outdoor sun causes sunscald on the soft, indoor-grown leaves, and the temperature shock stresses recently-active root systems.

Start hardening off in late April to early May:

1. Day 1–3: Move plants to a sheltered spot outdoors (partial shade, wind protection) for 1 to 2 hours, then bring back inside.
2. Day 4–7: Increase outdoor time to 3 to 4 hours, gradually introducing direct morning sun.
3. Day 8–10: Plants can stay outside during the day; bring in if overnight temperatures will drop below 45°F.
4. After Day 10: Plants are ready to stay out overnight once nights consistently stay above 45°F.

In zone 6, late frosts can still occur in early May — monitor the forecast during hardening and move plants back inside on nights below 40°F. One unexpected hard frost during this window can undo weeks of careful overwintering.

Common Zone 6 Problems

For a detailed look at leaf color diagnosis, see our guide to geranium leaves turning yellow.

Frequently Asked Questions

Can geraniums come back on their own in zone 6?
No. Pelargoniums (the plants sold as bedding geraniums) cannot survive zone 6 winters outdoors — a single hard freeze kills them. If you want a geranium-like plant that returns each spring without intervention, look at true hardy geraniums, also called cranesbill (Geranium spp.) — cold-hardy perennials in zones 3 to 8 that are entirely different plants. For the full distinction, see our geranium vs. pelargonium breakdown.

How long do geraniums bloom in zone 6?
With regular deadheading, zonal geraniums bloom continuously from late May through the first hard frost — typically October in most of zone 6. That’s roughly 4 to 5 months of color from a single plant. Ivy types perform nearly as long when given afternoon shade in peak summer.

Why are my overwintered geraniums not blooming as well as they did last year?
Old wood produces fewer flowers. When you revive overwintered plants in March, cut back more aggressively than feels comfortable — trim to within 4 to 6 inches of the base if the stems are thick and woody. This forces new growth from lower nodes and restores the vigorous branching that supports heavy bloom. Feed with balanced fertilizer when fresh growth appears.

Should I deadhead before overwintering?
Yes — and do more than deadhead. Remove all flowers, buds, and yellowing leaves before bringing plants indoors or preparing them for bare-root storage. Spent plant material invites Botrytis, which can spread quickly in the warm, reduced-airflow conditions of indoor storage. [1]

Sources

[1] Annual Geranium (Pelargonium) — Clemson Cooperative Extension, Home & Garden Information Center

[2] Growing Annual Geraniums — Iowa State University Extension, Yard and Garden

[3] Overwintering Tender Geraniums — Wisconsin Horticulture, University of Wisconsin–Madison Extension (2024)

[4] How to Overwinter Geraniums for Next Year’s Garden — Illinois Extension, University of Illinois (2024)