How to protect plants from late spring frost?

Late spring frosts are a real concern in New Brunswick, where frost can occur well into May and even early June in some areas. The key is monitoring weather forecasts closely and having protection methods ready to deploy quickly when temperatures are expected to drop below 2°C.

Understanding NB's Frost Risk

New Brunswick's last frost dates vary significantly by location — Saint John typically sees its last frost around May 15th, Fredericton around May 20th, while northern areas like Bathurst can experience frost into early June. Even after the average last frost date, unexpected cold snaps can damage tender plants. This is why experienced NB gardeners wait until after the May long weekend to plant tender annuals and vegetables.

Immediate Protection Methods

For plants already in the ground, frost cloth or row covers are your best defense. These lightweight fabrics can protect plants down to about -2°C while still allowing light and air circulation. Drape them over plants in late afternoon when frost is forecast, ensuring the fabric reaches the ground to trap soil heat. Remove covers the next morning once temperatures rise above freezing.

Water-filled wall-o-water protectors work exceptionally well for individual tomato plants or peppers. The water absorbs heat during the day and releases it slowly at night, creating a warm microclimate. For larger areas, old bedsheets, blankets, or even cardboard boxes can provide emergency protection, though they're less effective than proper frost cloth.

Creating Microclimates

Position tender plants near south-facing walls or large rocks that absorb and radiate heat. Avoid low-lying areas where cold air settles — even a few feet of elevation can make the difference between frost damage and healthy plants. Mulching around plants helps insulate roots and retain soil heat, but pull mulch slightly away from plant stems to prevent moisture buildup.

Watering Strategy

Water plants thoroughly the day before expected frost — moist soil holds more heat than dry soil and releases it slowly overnight. However, avoid watering the morning after frost, as rapid temperature changes can shock already-stressed plants.

Container Plant Protection

Move potted plants into an unheated garage, shed, or even against the house foundation where they'll be several degrees warmer. If you can't move them, group containers together and wrap the entire group with frost cloth or blankets. The thermal mass of multiple pots helps maintain temperature.

When to Hire a Professional

While frost protection is typically a DIY task, consider hiring a landscaper if you have extensive garden beds, valuable specimen plants, or a large property where covering everything becomes overwhelming. Professional landscapers can also help design your garden layout to minimize frost risk through proper plant placement and microclimate creation.

Long-term Planning

Choose cold-hardy varieties and plant tender species in protected locations. Many NB gardeners successfully grow borderline-hardy plants by selecting sheltered spots and using season extenders. Remember that even hardy perennials can suffer damage if they've started new growth and then experience a hard frost.

Need help designing a garden that minimizes frost risk? New Brunswick Landscaping can match you with local professionals who understand our challenging Maritime climate and can help create microclimates that extend your growing season.