Planting Guides
When to Plant Kale in Philadelphia: Complete Guide + Best Varieties for Zone 7a
Philadelphia, Pennsylvania
USDA Zone 7a
Last Frost: Apr 10
Last updated: October 30, 2025
Philadelphia gardeners can plant kale twice yearly: early spring (March 15-April 1) and late summer (August 1-15) for optimal harvests in Zone 7a.
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Quick Answer
Plant kale in Philadelphia March 15-April 1 for spring harvest or August 1-15 for fall harvest. Fall plantings produce superior flavor after October frosts.
TL;DR
Philadelphia kale thrives with two annual plantings. Plant spring crops March 15-April 1 for May-July harvest before summer heat. Plant fall crops August 1-15 for September-December harvest with superior flavor after frost. Brassica oleracea 'Winterbor' and Brassica oleracea 'Lacinato' excel in Philadelphia's Zone 7a climate with potential overwintering protection.
Frequently Asked Questions
When is the absolute best time to plant kale in Philadelphia for maximum flavor?
Plant kale August 1-15 for fall harvest beginning in October. This timing allows plants to mature as temperatures cool, then develop superior sweetness after Philadelphia's first frost around November 4. Fall-planted kale consistently outperforms spring crops in both flavor and tenderness. The combination of warm soil for establishment and cool air temperatures for growth creates ideal conditions that spring planting cannot match.
Can kale survive Philadelphia winters outdoors without a greenhouse?
Yes, kale overwinters successfully in Philadelphia's Zone 7a climate with minimal protection. Brassica oleracea 'Winterbor' and Brassica oleracea 'Redbor' survive temperatures down to 10°F (-12°C) when properly established. Apply 4-6 inches of straw mulch in November and use lightweight row covers during extended cold spells below 15°F (-9°C). Many Philadelphia gardeners harvest fresh kale throughout winter with this simple protection method.
Why does my spring-planted kale turn bitter and flower in early summer?
Spring kale bolts (flowers) when exposed to sustained temperatures above 80°F (27°C), which typically occurs in Philadelphia during June-July. This natural response makes leaves bitter and tough. Choose bolt-resistant varieties like Brassica oleracea 'Red Russian' for spring planting, or focus on fall crops that mature in cooling temperatures. Spring kale should be harvested completely by mid-July to avoid quality degradation from heat stress.
How do I prevent cabbage worms from destroying my Philadelphia kale crop?
Install floating row covers immediately after planting to prevent cabbage white butterflies from laying eggs on plants. For established plants, apply Bt (Bacillus thuringiensis) spray weekly during active pest periods (May-June and August-September). This organic bacterial spray specifically kills caterpillars without harming beneficial insects. Hand-picking larger caterpillars also provides effective control in small gardens.
What's the difference between growing kale in containers versus garden beds in Philadelphia?
Container kale requires more frequent watering and feeding but offers better control over soil conditions and pest management. Use containers at least 12 inches deep and wide for single plants, with drainage holes and quality potting mix. Brassica oleracea 'Vates' works best for containers due to its compact 12-16 inch height. Garden beds provide more consistent moisture and nutrients but require soil amendment for Philadelphia's heavy clay. Both methods work well when properly managed.
How often should I plant new kale seeds for continuous harvest in Philadelphia?
Plant small amounts every 2-3 weeks during optimal periods for continuous harvest. Spring succession: March 15, April 1, and April 15. Fall succession: August 1, August 15, and September 1. This staggered approach provides fresh young leaves continuously and protects against total crop loss from weather or pest issues. Each planting produces harvestable leaves for 8-12 weeks using cut-and-come-again harvesting methods.
Can I grow kale year-round in Philadelphia, or only seasonally?
Philadelphia's Zone 7a climate supports nearly year-round kale production with proper planning. Plant spring crops March-April for May-July harvest, then fall crops August for October-March harvest with winter protection. The gap occurs during hottest summer months (late July-September) when heat causes bolting and poor quality. Pacific Northwest gardeners can grow year-round, but Philadelphia requires this two-season approach for best results.
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Frank Russo
Frank retired from the city parks department after 28 years, the last fifteen as a grounds supervisor overseeing park plantings and maintenance crews. He now spends his time volunteering at a local historic garden, maintaining his own half-acre property in the Roxborough neighborhood, and writing about landscape maintenance, seasonal timing, and the practical side of keeping plants healthy through Mid-Atlantic winters and humid summers. Frank knows what works at scale and what's a waste of time—he's planted thousands of trees and shrubs and watched plenty of them fail. His advice tends toward what's proven and durable rather than what's trendy.
