Last Frost Date Planting Guide for Pittsburgh Area Gardeners

In the early days of spring and again in the fall, our Pittsburgh, Pennsylvania, gardens can fall victim to a sneaky threat: frost. It may be bright and sunny during the day, but if overnight temps dip too low, tender plants can suffer — or worse, be lost for the season.

If you’re wondering when to plant in Pittsburgh, the key is understanding your last frost date, and how unpredictable spring weather can be in Western Pennsylvania.

Understanding the Last Frost Date in Pittsburgh

The average last frost date in Pittsburgh (USDA Zone 6) is around May 15. But here’s the catch: that date isn’t a guarantee. It simply means there’s about a 90% chance we won’t see another frost after that point.

Cold snaps can still happen.

That’s why we always recommend watching the forecast closely, especially if you’re planting early or growing frost-sensitive plants like:

• Tomatoes 
• Basil 
• Peppers 
• Annual flowers 
• Tropical plants 

Most of these plants begin to experience stress when temperatures drop below 45°F, even if frost doesn’t fully form.

HOW TO SHIELD YOUR PLANTS FROM THE COLD

When a frost or freeze advisory pops up, here’s how you can step in and help your plants survive:

• Bring them in: Potted plants are easy to move. Bring them into your garage, greenhouse, or indoors overnight.
• Cover them up: For plants already in the ground, use frost blankets, old sheets, lightweight blankets, or even cardboard. These insulate plants and trap heat. Avoid plastic — it doesn’t insulate well and can do more harm than good.
• Don’t forget about perennials: Even hardy plants can be vulnerable if they’ve been living the cozy greenhouse life and haven’t acclimated (a process we call “hardening off”).

What Is Hardening Off (and Why It Matters)

If you’ve ever brought home beautiful plants from a greenhouse and planted them right away, only to watch them struggle, you’ve likely run into an issue called lack of hardening off.

Hardening off plants is the process of gradually acclimating them to outdoor conditions like sun, wind, and fluctuating temperatures.

Plants grown in greenhouses or indoors live a pretty cushy life:

• Stable temperatures
• Filtered light
• No wind

Moving them outside too quickly can shock the plant, causing leaf burn, stunted growth, or increased vulnerability to cold, even if temperatures are technically “safe.

How to Harden Off Plants (Step-by-Step)

To safely transition plants outdoors, follow this simple 7–10 day process:

Day 1–2:
Place plants outside in a shady, protected area for 2–3 hours, then bring them back inside.

Day 3–5:
Gradually increase time outdoors and introduce morning sun.

Day 6–7:
Extend exposure to more direct sunlight and longer outdoor periods.

Day 8–10:
Leave plants outside most of the day and, if nighttime temps stay above 50°F, begin leaving them out overnight.

Pro tip: Avoid hardening off during extreme conditions like strong winds, heavy rain, or unexpected cold snaps.

Don’t Forget About Hardening Off Perennials

Even cold-hardy perennials can be vulnerable if they’ve been grown in a greenhouse and not properly hardened off. Early planting without acclimation can set them back or cause unnecessary stress.

WHAT DOES FROST DAMAGE LOOK LIKE?

If frost hits, plant cells freeze and rupture. Damage that’s often irreversible.

Signs of frost damage include:

• Blackened or translucent leaves 
• Wilted or soggy texture 
• Mushy stems

Sometimes it takes a day or two for damage to show up fully. When in doubt, wait it out and assess. If the damage isn’t too severe, the plant will often recover if you take precautions to prevent further damage, like covering.

Need a Backup Plan? Get Plant Starts from Your Local Greenhouse

Most vegetable seedlings need to be started 4-6 weeks before the last frost date. If you missed that window, or if your seedlings were damaged by the frost, support your local greenhouse. At Bedner’s Farm & Greenhouse we carry:

For vegetable seedlings, we have: 

Broccoli
Cabbage
Cauliflower
Kale
Leeks
Onion
Spinach
Strawberries
And more!

You can check our current inventory here.

Grow with Confidence This Season

At our core, we believe in setting you, and your plants, up for success from the very start. Understanding the last frost date in Pittsburgh, knowing when to plant, and properly hardening off your plants can make all the difference in a thriving garden.

Have questions about what to plant and when? Stop by and chat with us—we love talking plants!