Growing Guide: Arugula

Arugula is a fast-growing, peppery leafy green that serves as a perfect addition to any urban salad garden. As a cool crop, it thrives in the lower-light and cooler temperatures of spring and autumn. Because it reaches maturity quickly, often providing a first harvest in just 35 days, it’s an ideal candidate for succession planting before and after a summer crop to maximize your garden’s output throughout the season.  

Planting

  • Method: Arugula should be direct-seeded into your garden rather than transplanted.  
  • Timing: For a spring crop, plant outdoors approximately 1-2 weeks before the last frost date (typically mid-to-late April in Toronto), though it can usually be planted as early as late-March if there’s no frost in the weather forecast, as it is frost-hardy. For a fall harvest, you can start new seeds in late August or early September, and even into late September if the crop is protected.  
  • Location and Sun: Select a spot with partial shade to full sun, though morning sunlight is preferable to late-day sunlight. If you attempt to plant arugula during the heat of summer, select a cool, shady spot to reduce the likelihood of bolting.  
  • Soil and Spacing: Plant into loose, well-drained soil enriched with compost. If you plan on harvesting full heads of arugula, use 6” spacing.  If you plan on harvesting individual leaves, then space seeds approximately 4″ apart.  
  • Germination: Seeds typically germinate in 4–7 days when soil temperatures are between 20°C and 25°C. They can also germinate in soil temperatures as low as 4°C, though it will take a few extra days.  

Maintenance

  • Watering: Keep the soil constantly moist until the seeds germinate. Once established, ensure the soil stays damp but not sopping wet to allow for adequate oxygen at the root level.  
  • Feeding: Arugula is a light-feeder, so it doesn’t need much fertilizer. However, as a leafy green, arugula benefits from nitrogen-focused organic supplements in particular to encourage foliage growth.  
  • Safety Note: Avoid using manure on low-growing greens like arugula to minimize the risk of E. coli contamination.  
  • Weather Mitigation: If temperatures rise above 28°C, arugula may “bolt,” meaning it will send up a flower stalk and the harvest will become bitter. Use shade cloth or place taller plants nearby to provide afternoon shade to delay this process.  

Pests and Diseases

  • Common Pests: Like other leafy greens, arugula is susceptible to aphids, slugs, and snails. As a member of the mustard family, it may also be targeted by flea beetles, which create many tiny holes in the leaves.  
  • Management: Use fine-mesh row covers to block flying insects like flea beetles from landing on your crop. For slugs and snails, create a circle of diatomaceous earth around the base of your plants.  
  • Disease: Ensure proper spacing and avoid overwatering to prevent gray mold and powdery mildew.  

Harvesting

  • Timing: You can begin harvesting individual leaves once they reach your preferred size; they are considered mature when they are at least 4″ long.  
  • Technique:
    • Cut-and-Come-Again: Remove outer leaves individually or else horizontally slice off the top of the leaves at a level of 2.5″ above the soil level. The plant will regrow, allowing for 3–4 harvests from the same plant.  
    • Whole Head: Cut the entire head at the soil level once it reaches full size.  
  • Storage: Store arugula in air-tight containers in the refrigerator to maintain freshness.  

💡 Tips for Toronto Gardeners 💡

In our local climate, the spring greens window can be surprisingly short before the heat and humidity hits. Try planting a small patch every week starting in mid-April. This spreads out your harvest and, also, provides protection via, if one batch bolts due to a sudden May heatwave, you’ll have a younger, more resilient crop right behind it ready to take its place.

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