When To Plant Broccoli In Pa

Pennsylvania’s short growing season means broccoli seeds need to hit the soil by early August for a fall harvest, or late March for spring. Knowing when to plant broccoli in PA is the single biggest factor between a heavy harvest and a tray of bitter, buttoned heads. The state’s USDA hardiness zones range from 5a in the northern tier to 7b in the southeast, so your exact date will shift by a week or two depending on where you live.

Broccoli is a cool-weather crop. It hates the heat. If the temperature spikes above 80°F while the head is forming, you will get loose, leafy florets that bolt to seed almost overnight. That is why timing is not just a suggestion—it is a hard rule.

In this guide, you will learn the exact planting windows for every region in PA, how to start seeds indoors, and how to protect your crop from frost and pests. We will also cover the common mistakes that ruin broccoli in Pennsylvania backyards.

For the majority of Pennsylvania, you have two distinct planting windows. The first is for a spring crop, and the second is for a fall crop. The fall crop is often more reliable because the weather cools down as the heads mature, which is exactly what broccoli wants.

Here is the simple breakdown:

Spring crop: Start seeds indoors 6-8 weeks before the last frost. Transplant outdoors 2-3 weeks before the last frost date.
Fall crop: Start seeds indoors in mid-June. Transplant outdoors in mid-to-late July. Or direct sow in early August.

Let us break this down by region, because Erie and Philadelphia are not the same climate.

Eastern Pennsylvania (Zones 6B-7b)

If you live near Philadelphia, Allentown, or the Lehigh Valley, your last spring frost usually lands between April 10 and April 20. Your first fall frost is around October 20 to November 5.

For the spring crop, transplant broccoli seedlings outdoors between March 25 and April 5. They can handle a light frost, but if a hard freeze is forecast, you need row cover.

For the fall crop, transplant seedlings into the garden between July 20 and August 1. Direct sowing seeds in the ground can be done from August 1 to August 10, but you will need to keep the soil consistently moist for germination.

Central Pennsylvania (Zones 5B-6a)

This includes Harrisburg, State College, and Williamsport. The last frost is usually around April 25 to May 5. The first fall frost hits around October 10 to October 20.

Spring transplanting should happen between April 5 and April 15. If you plant too early, the cold soil will stunt the roots and the plant will sit there doing nothing for weeks.

For the fall crop, transplant between July 15 and July 25. Direct sowing can happen from July 25 to August 5. You have a slightly tighter window here, so do not delay.

Western Pennsylvania (Zones 5A-6b)

Pittsburgh and the western counties have a last frost around April 20 to May 1. The first fall frost is around October 5 to October 15.

Spring transplants go out between April 1 and April 15. Fall transplants go out between July 10 and July 20. Direct sowing for fall should be done by July 25 at the latest.

In the northern tier, like Bradford or Warren counties, you are in zone 5a. Your growing season is about 20 days shorter than Philadelphia. Adjust all dates by one week earlier for fall and one week later for spring.

How To Start Broccoli Seeds Indoors

Starting broccoli indoors is not difficult, but you need to do it at the right time. If you start too early, the seedlings become leggy and root-bound. If you start too late, they will not have enough size to survive transplant shock.

Count backwards from your transplant date. For spring, count back 6 weeks from your target transplant date. For fall, count back 5 weeks from your target transplant date.
Use a seed starting mix. Do not use garden soil. It is too heavy and may contain damping-off fungus.
Plant seeds 1/4 inch deep. Broccoli seeds need darkness to germinate.
Keep the soil at 70°F. Use a heat mat if your house is cold.
Provide light immediately after germination. A sunny windowsill is usually not enough. Use a grow light for 14-16 hours per day.
Harden off for 7-10 days. This means gradually exposing the seedlings to outdoor conditions. Start with 1 hour of shade, then increase daily.

Do not skip the hardening off step. If you transplant seedlings directly from a warm windowsill into the cold PA spring soil, they will suffer transplant shock. The leaves will turn purple and the plant may bolt prematurely.

Direct Sowing Broccoli In Pennsylvania

Direct sowing is only recommended for the fall crop. Spring soil in PA is too cold and wet for reliable germination. Broccoli seeds will rot in cold, soggy ground.

For direct sowing in August, follow these steps:

Choose a spot with full sun (at least 6 hours).
Amend the soil with compost. Broccoli is a heavy feeder.
Sow seeds 1/2 inch deep, 3 inches apart.
Water gently but thoroughly. Keep the top inch of soil moist.
Thin seedlings to 18 inches apart once they have two sets of true leaves.

The key challenge with August sowing is heat. The soil temperature might be 80°F, which is too warm for broccoli seeds. They prefer soil between 45°F and 75°F. You can shade the soil with a board or a piece of burlap until the seeds germinate, which usually takes 7-10 days.

Soil Preparation And Fertilizer

Broccoli is a heavy feeder. It needs rich, well-draining soil with a pH between 6.0 and 7.0. Before planting, work in 2-3 inches of compost or aged manure.

You should also add a balanced fertilizer, like a 10-10-10, at planting time. But be careful with nitrogen. Too much nitrogen early on will give you huge leaves and tiny heads.

Here is a simple feeding schedule:

At transplant: Mix 1 tablespoon of 10-10-10 fertilizer into the bottom of each planting hole.
3 weeks later: Side-dress with a nitrogen-rich fertilizer like blood meal or fish emulsion.
When the head starts to form: Side-dress again with a low-nitrogen fertilizer, like 5-10-10.

Mulch around the plants with straw or shredded leaves. This keeps the soil cool, which is critical for broccoli in PA. Cool soil means the roots stay happy and the plant is less likely to bolt.

Transplanting Broccoli Seedlings

When your seedlings are 4-6 weeks old and have 4-5 true leaves, they are ready to go outside. Choose a cloudy day or transplant in the late afternoon to reduce stress.

Space the plants 18 inches apart in rows that are 24-36 inches apart. Broccoli plants grow large. If you crowd them, they will compete for water and nutrients, and the heads will be small.

Plant the seedlings slightly deeper than they were in the pot. Bury the stem up to the first set of leaves. This encourages more root growth.

Water deeply after transplanting. Add a starter solution of liquid fertilizer to help the roots establish.

Protecting Broccoli From Frost

Broccoli is cold-hardy. It can survive light frosts (down to 28°F) without damage. But a hard freeze (below 25°F) will kill the plant or ruin the head.

For the spring crop, you need to be ready to cover your plants if a late frost is forecast. Use row cover, old bedsheets, or plastic sheeting. Remove the cover in the morning when the temperature rises above freezing.

For the fall crop, frost is actually beneficial. A light frost improves the flavor of broccoli, making it sweeter. You can leave your fall broccoli in the ground until the temperature drops below 25°F.

Common Pests And Problems

Pennsylvania gardeners face a few specific broccoli pests. The most common are:

Cabbage worms: These are the green caterpillars that chew holes in the leaves and get into the heads. Check the underside of leaves for eggs. Hand-pick them or use BT (Bacillus thuringiensis).
Aphids: These tiny insects cluster on the underside of leaves. Blast them off with a strong stream of water or use insecticidal soap.
Flea beetles: These small black beetles chew tiny holes in the leaves. Use row cover to keep them off young plants.

Another common problem is “buttoning.” This is when the plant produces a tiny, marble-sized head instead of a full head. Buttoning is caused by stress, usually from cold soil, drought, or transplant shock. The best prevention is to plant at the right time and keep the soil consistently moist.

Harvesting Broccoli

Broccoli is ready to harvest when the head is fully formed but the buds are still tight and dark green. If you see yellow petals starting to show, you waited too long. The head will be bitter and woody.

Cut the main head with a sharp knife, leaving 5-6 inches of stem. Do not pull the plant out of the ground. After you cut the main head, the plant will produce side shoots. These are smaller heads that grow from the leaf axils. You can harvest these for several more weeks.

For a fall crop, you can often harvest broccoli well into November. The heads will hold in the garden for a long time in cool weather. Just pick them before a hard freeze.

Succession Planting For Continuous Harvest

If you want a steady supply of broccoli, do not plant everything at once. Instead, use succession planting. Plant a few seedlings every 2 weeks.

For the spring crop, you can stagger your transplanting from late March to mid-May. For the fall crop, stagger from mid-July to mid-August. This gives you a continuous harvest instead of a single glut.

Keep in mind that broccoli does not like hot weather. If you plant a late spring crop that matures in June, the heads may be small and loose. It is better to focus your energy on the spring and fall windows.

Frequently Asked Questions

Can I Plant Broccoli In PA In September?

No, September is too late for a fall crop in most of Pennsylvania. The heads need 60-70 days to mature from transplanting. If you plant in September, the heads will not form before the hard frosts of November. Stick to the July and early August planting window.

What Is The Best Broccoli Variety For Pennsylvania?

For spring, choose fast-maturing varieties like ‘Green Goliath’ or ‘Packman’ that mature in 50-60 days. For fall, choose cold-hardy varieties like ‘Arcadia’ or ‘Waltham 29’ that can handle frost and have good side-shoot production.

How Much Cold Can Broccoli Seedlings Tolerate?

Broccoli seedlings can tolerate light frosts down to 28°F. They will survive short periods of 25°F, but growth will slow. If temperatures below 25°F are forecast, cover the plants with row cover or a cloche.

Why Is My Broccoli Not Forming A Head?

There are several reasons. The most common is that the plant is stressed by heat, drought, or cold soil. Another reason is too much nitrogen, which causes leafy growth instead of head formation. Finally, the plant may not have had enough time to mature. Check your days-to-maturity and your planting date.

Can I Grow Broccoli In Containers In PA?

Yes, but you need a large container. Use a pot that is at least 5 gallons and 12 inches deep. Broccoli has a large root system. Container-grown broccoli will need more frequent watering and fertilizing than garden-grown plants.

Final Tips For Pennsylvania Broccoli Success

Here is a quick recap of the most important points:

Know your frost dates. Write them down on a calendar.
Start seeds indoors for the spring crop. Direct sow only for the fall crop.
Keep the soil cool with mulch. Broccoli hates hot roots.
Water consistently. Inconsistent watering causes bitter heads.
Harvest before the buds open. Check your plants daily once the heads start to form.

Pennsylvania’s climate is actually ideal for broccoli if you time it right. The cool springs and crisp falls are exactly what this crop needs. You just have to avoid the summer heat.

One more thing. Keep a garden journal. Write down when you planted, when you harvested, and what worked. Next year, you will have your own personal data for your specific microclimate. That is more accurate than any generic guide.

Now go get those seeds in the ground. The window is open, and it closes faster than you think.