Pennsylvania’s varied elevation zones require adjusting flower planting schedules by two to three weeks. Finding the best time to grow flowers in Pennsylvania depends on your specific location, from the lowlands of Philadelphia to the high ridges of the Alleghenies.
Most gardeners in the Keystone State face a short growing season, especially in the north and west. But with a solid plan, you can enjoy blooms from early spring through the first frost.
This guide breaks down planting times by region, flower type, and practical steps. No fluff—just clear, actionable advice.
Best Time To Grow Flowers In Pennsylvania
The ideal window for planting flowers in Pennsylvania runs from mid-April to late May for spring planting. For fall blooms, aim for late August to early October.
But these dates shift based on your elevation and microclimate. Let’s get specific.
Understanding Pennsylvania’s Hardiness Zones
Pennsylvania spans USDA hardiness zones 5a to 7b. This means average minimum winter temperatures range from -20°F to 5°F. Your zone directly impacts when you can safely plant.
- Zone 5a/b (northern and central highlands): Last frost around May 15–25. First frost around September 20–October 5.
- Zone 6a/b (most of central and southeast): Last frost around April 25–May 10. First frost around October 5–15.
- Zone 7a/b (southeast corner, Philadelphia area): Last frost around April 1–15. First frost around October 15–30.
Check your specific zone using the USDA map. Your local county extension office can give you precise frost dates.
Spring Planting: The Main Event
Spring is when most flowers go in the ground. The key is waiting until soil warms up and frost danger passes.
Cool-Season Annuals (Plant Early)
These flowers tolerate light frost and can go in 2–3 weeks before your last frost date.
- Pansies
- Violas
- Snapdragons
- Dianthus
- Calendula
In Zone 6, plant these around mid-April. In Zone 5, wait until late April or early May.
Warm-Season Annuals (Plant After Frost)
These need warm soil and air temperatures. Plant them after your last frost date.
- Marigolds
- Zinnias
- Petunias
- Impatiens
- Begonias
In Zone 6, aim for mid-May. In Zone 5, late May to early June is safer.
Fall Planting: Perennials And Bulbs
Fall is prime time for planting perennials, shrubs, and spring-blooming bulbs. The soil is warm, and roots establish before winter.
Spring-Blooming Bulbs
Plant tulips, daffodils, crocuses, and hyacinths in fall. They need a cold period to bloom.
- Wait until soil temperatures drop below 60°F (usually late September to October).
- Plant bulbs 2–3 times as deep as their height.
- Water well after planting.
In northern PA, plant bulbs by mid-October. In the south, you have until early November.
Perennials
Fall is excellent for planting perennials like coneflowers, black-eyed Susans, and sedums. They get a head start on root growth.
Plant at least 6 weeks before the ground freezes. In Zone 5, that means by early September. In Zone 7, you can plant into October.
Summer Planting: Possible But Tricky
You can plant flowers in summer, but heat stress is a real issue. If you must plant in July or August, choose heat-tolerant varieties.
- Portulaca
- Lantana
- Cosmos
- Salvia
- Verbena
Water deeply and frequently. Mulch around plants to keep soil cool. Avoid planting during heat waves.
Regional Adjustments For Pennsylvania
Elevation changes everything. Here’s how to adjust for your area.
Southeastern Pennsylvania (Zones 6b–7b)
This region includes Philadelphia, Allentown, and Reading. It’s the warmest part of the state.
Start seeds indoors in late February. Plant cool-season flowers in early April. Warm-season flowers go out in early to mid-May.
You can often get a second planting of fast-growing annuals in late July for fall color.
Central Pennsylvania (Zones 6a–6b)
Areas like Harrisburg, State College, and Lancaster fall here. Springs are moderate, but frost can linger.
Start seeds indoors in early March. Plant cool-season flowers in late April. Warm-season flowers go out in mid-to-late May.
Watch for late frosts in May. Keep row covers handy.
Northern and Western Pennsylvania (Zones 5a–5b)
This includes Erie, Scranton, and the Poconos. Winters are harsh, and summers are short.
Start seeds indoors in mid-March. Plant cool-season flowers in early May. Warm-season flowers go out in late May or early June.
Choose short-season varieties. Look for flowers that mature in 60 days or less.
High Elevation Areas (Zones 4b–5a)
Some mountain peaks and high plateaus in the Alleghenies are even colder. Here, the growing season can be just 90 days.
Focus on cold-hardy perennials and fast-growing annuals. Plant after June 1. Use season extenders like cold frames or row covers.
Starting Seeds Indoors: A Head Start
For many flowers, starting seeds indoors gives you a jump on the season. This is especially helpful in northern PA.
- Check the seed packet for “weeks to transplant.” Count back from your last frost date.
- Use seed-starting mix, not garden soil.
- Provide 14–16 hours of light daily.
- Harden off seedlings for 7–10 days before planting outside.
For warm-season flowers, start seeds 6–8 weeks before your last frost. For cool-season flowers, 4–6 weeks is enough.
Direct Sowing: When To Plant Seeds Outside
Some flowers prefer direct sowing. They don’t transplant well or grow fast enough to need indoor starts.
Cool-Season Direct Sow (Early Spring)
- Sweet peas
- Larkspur
- Poppies
- Bachelor’s buttons
Sow these as soon as soil can be worked, usually March or early April.
Warm-Season Direct Sow (Late Spring)
- Zinnias
- Sunflowers
- Cosmos
- Nasturtiums
Sow these after soil reaches 60°F, typically mid-May to early June.
Soil Preparation: Don’t Skip This
Good soil makes everything easier. Test your soil pH and amend as needed.
- Most flowers prefer pH 6.0–7.0.
- Add compost to improve drainage and fertility.
- Work soil when it’s moist but not wet.
In heavy clay areas (common in parts of PA), raised beds or containers work well.
Mulching And Watering Tips
Mulch helps regulate soil temperature and retain moisture. Apply 2–3 inches of organic mulch after planting.
Water deeply but infrequently. Most flowers need 1 inch of water per week. In sandy soils, water more often.
Drip irrigation is ideal. It keeps foliage dry and reduces disease.
Common Mistakes To Avoid
Even experienced gardeners make these errors. Steer clear.
- Planting too early. Cold soil kills roots.
- Planting too late. Flowers may not mature before frost.
- Overwatering. Soggy soil causes root rot.
- Ignoring spacing. Crowded plants compete for nutrients.
- Forgetting to harden off seedlings. They need gradual exposure.
Season Extension Techniques
Want to push your season longer? Try these methods.
Row Covers
Floating row covers add 2–4 weeks to your season. They protect from light frost and wind.
Cold Frames
A simple cold frame lets you start seeds earlier and harden off plants safely. Place it in a sunny spot.
Mulching for Winter Protection
After the ground freezes, add a thick layer of straw or leaves over perennial beds. This prevents frost heave.
Flower Selection By Bloom Time
Plan for continuous color from spring to fall.
Early Spring (March–April)
- Crocus
- Snowdrops
- Hellebores
- Pansies
Late Spring (May–June)
- Tulips
- Daffodils
- Lilacs
- Peonies
Summer (July–August)
- Daylilies
- Echinacea
- Black-eyed Susans
- Lavender
Fall (September–October)
- Chrysanthemums
- Asters
- Sedums
- Ornamental kale
Dealing With Pennsylvania’s Weather Challenges
Pennsylvania weather is unpredictable. Late frosts, heavy rain, and drought happen.
Keep frost cloth handy in spring. Have a watering plan for dry spells. Improve drainage in areas that stay wet.
Choose disease-resistant varieties. Powdery mildew and botrytis are common in humid summers.
Native Flowers For Easier Gardening
Native plants are adapted to Pennsylvania’s climate. They need less water and fertilizer.
- Butterfly weed (Asclepias tuberosa)
- Wild columbine (Aquilegia canadensis)
- Blue false indigo (Baptisia australis)
- Joe-pye weed (Eutrochium purpureum)
Plant natives in spring or fall. They establish quickly and support local pollinators.
Container Gardening: Flexible Timing
Containers warm up faster than ground soil. You can plant a bit earlier in spring.
Use potting mix, not garden soil. Choose compact varieties. Water daily in hot weather.
Move containers indoors or to a sheltered spot if frost threatens.
Fertilizing For Best Blooms
Flowers need nutrients to bloom well. Use a balanced fertilizer (10-10-10) at planting time.
For annuals, fertilize every 2–4 weeks during the growing season. For perennials, one application in spring is often enough.
Avoid high-nitrogen fertilizers. They promote leaves, not flowers.
Deadheading And Pruning
Remove spent flowers to encourage more blooms. This is called deadheading.
Cut back perennials in late fall or early spring. Leave some seed heads for winter interest and birds.
Pest And Disease Management
Common pests in Pennsylvania include aphids, slugs, and Japanese beetles.
- Use insecticidal soap for aphids.
- Handpick beetles and slugs.
- Encourage beneficial insects like ladybugs.
Prevent diseases by spacing plants properly and watering at soil level.
Frequently Asked Questions
Can I plant flowers in Pennsylvania in July?
Yes, but choose heat-tolerant varieties like portulaca or lantana. Water deeply and mulch well. Avoid planting during heat waves.
What is the latest time to plant perennials in Pennsylvania?
Plant perennials at least 6 weeks before the ground freezes. In northern PA, that’s early September. In the south, you have until mid-October.
Do I need to protect flowers from frost in Pennsylvania?
Yes, especially in spring and fall. Use row covers, cloths, or bring containers indoors. Know your local frost dates.
What flowers grow best in Pennsylvania’s climate?
Native plants like butterfly weed, coneflowers, and black-eyed Susans thrive. Also, pansies, marigolds, and zinnias are reliable choices.
When should I start flower seeds indoors in Pennsylvania?
Start warm-season seeds 6–8 weeks before your last frost. Cool-season seeds 4–6 weeks before. Check your zone for exact dates.
Final Thoughts On Timing
Knowing the best time to grow flowers in Pennsylvania comes down to your zone and the flower type. Use frost dates as your guide, not the calendar.
Keep a garden journal. Note when you planted and how things performed. Over time, you’ll fine-tune your schedule.
Start small if you’re new. Pick a few easy flowers and expand each year. Your garden will reward you with color from spring through fall.