Parsley adds a fresh, vibrant flavor to many dishes. Its successful cultivation relies on understanding its temperature requirements, which are crucial from germination to growth and flavor development.
Ideal Temperature Range for Parsley
For successful germination, parsley seeds prefer soil temperatures between 65–70°F (18–21°C). The optimal temperature for parsley seed germination is around 80°F (27°C). This warmth helps overcome the slow germination period of parsley, which can take between two to six weeks.
Once germinated, parsley thrives in cooler temperatures, ideally between 40°F (4.4°C) and 75°F (23.9°C). An optimal growing range is 50-70°F (10-21°C) for overall vigor and leaf development. Maintaining temperatures within this range promotes robust growth and the best flavor profile.
How Cold Temperatures Affect Parsley
Parsley exhibits cold hardiness, but temperatures below its ideal range can still cause damage. While it can survive light frost, growth slows when temperatures drop below 45°F (7°C). Exposure to temperatures around 20°F (-6.7°C) or lower can lead to wilting, leaf discoloration, and plant demise.
In severe cold, leaves may darken, and the plant can suffer from water-soaked necrosis. Although parsley is a biennial that can often survive one winter, prolonged hard freezes can kill the plant. Young seedlings exposed to cold are also more prone to bolting prematurely in their second season.
How Hot Temperatures Affect Parsley
Temperatures exceeding parsley’s preferred range negatively impact its growth and quality. Above 70°F (21°C), parsley growth can slow. High heat, particularly above 86°F (30°C), often triggers bolting, where the plant prematurely sends up a flower stalk and goes to seed.
Bolting typically results in a reduction of the plant’s desirable leafy growth, and the flavor of the leaves can become bitter. Additionally, sustained temperatures above 90°F (32°C) can cause leaves to yellow, scorch, or become more susceptible to sunburn, impacting both the plant’s health and its visual appeal. The plant may also become more prone to pest issues under heat stress.
Seasonal Planting Based on Temperature
Understanding parsley’s temperature preferences is essential for determining optimal planting times. As a cool-season herb, parsley is best planted in early spring, once the soil can be worked, typically three to four weeks before the last expected frost. This timing allows the plant to establish itself and grow vigorously during the cooler spring months.
In regions with mild winters, a second planting can occur in late summer or early fall. This autumn sowing provides a fresh supply of leaves through the cooler fall and winter, extending the harvesting season. Different climate zones will influence these windows; for instance, in warmer climates like Florida, planting in fall or early spring takes advantage of cooler temperatures and avoids intense summer heat.
Protecting Parsley from Temperature Extremes
Protecting parsley from temperature extremes helps ensure a continuous harvest and prevents plant stress. To guard against cold, apply a 1-2 inch layer of mulch around the plant base, which insulates the soil and helps maintain consistent temperatures. Row covers can provide additional protection during light frosts, trapping warmth around the plants.
For potted parsley, moving plants indoors to a cool, well-lit location, such as a sunny windowsill, can protect them from harsh winter conditions. When facing high summer temperatures, providing partial shade during the hottest part of the day can prevent bolting and leaf scorch. Consistent watering is also crucial in hot weather to keep the soil moist and mitigate heat stress.