Nasturtiums are a vibrant and versatile plant known for their fast growth, bright, edible flowers, and peppery-tasting leaves. USDA Hardiness Zone 9 is characterized by mild winters and a long growing season. Since the last frost typically occurs around late January or early February, this allows for an extended period of cultivation. Nasturtiums flourish in these conditions, providing color and culinary interest.
Specific Planting Times for Zone 9
The mild climate of Zone 9 allows for an earlier and longer planting window for nasturtiums compared to colder regions. Since nasturtiums are tender plants, direct sowing should begin after the last frost, which typically occurs in late January or mid-February.
Gardeners can start direct sowing seeds from late January through March for the main spring and early summer flush of blooms. Optimal germination occurs when the soil temperature is between 55°F and 65°F. Nasturtiums slow their blooming once temperatures consistently exceed 85°F, struggling in the intense heat of mid-summer.
To extend the flowering season, a second sowing can be planned for early fall, around September or October. This allows the plants to mature and bloom throughout the cooler late fall and mild winter months. Direct sowing is preferred because nasturtiums dislike root disturbance, making starting seeds indoors unnecessary.
Sowing Techniques for Optimal Germination
Nasturtium seeds have a hard outer shell, which can be modified to encourage faster water absorption and germination. Soaking the seeds in room temperature water for four to eight hours before planting speeds up the sprouting process. Alternatively, lightly scoring the seed coat with sandpaper or a nail file, a process called scarification, allows moisture to penetrate more easily.
Nasturtiums perform best in well-draining, lean soil with low fertility. Rich soil encourages excessive leaf growth at the expense of flowers, so avoid heavily amended garden beds. Sow the large seeds about a half-inch to one inch deep into the prepared soil.
Spacing should be adjusted based on the variety chosen. Dwarf or bush varieties typically need 8 to 12 inches of space. Trailing or vining varieties, such as those used for trellises or hanging baskets, require 12 to 24 inches between seeds to accommodate their greater spread.
Essential Care Requirements After Sprouting
Once the nasturtium seedlings have established their first set of true leaves, care shifts toward maintenance that encourages abundant blooming. These plants thrive in full sun, requiring a minimum of six to eight hours of direct sunlight daily for the best flower production. In the hottest parts of the Zone 9 summer, afternoon shade is beneficial, as it prevents the foliage from scorching.
Watering should be done infrequently but deeply once the plants are established to encourage a strong root system. Allow the top inch or two of soil to dry out between watering sessions, as overwatering leads to lush foliage but fewer flowers. Avoid fertilizing, especially with high-nitrogen products, since the plant’s preference for lean soil is key to a high flower-to-foliage ratio.
Nasturtiums are often used as a “trap crop” because they are highly attractive to common pests, especially aphids. If aphids infest the growing tips, a strong jet of water from a hose can dislodge them without chemical treatments. Regularly removing spent flowers, a process called deadheading, encourages the plant to produce new blooms throughout the long Zone 9 growing season.