USDA Hardiness Zone 9, characterized by average minimum winter temperatures between 20°F and 30°F, offers a long growing season. August marks a transition between the intense heat of summer and the productive fall and winter growing seasons. Successful gardening requires shifting focus from maintaining heat-stressed summer crops to preparing the soil and starting seeds for the cool-season harvest. This period is often called the “second spring,” as cooling air and still-warm soil create ideal conditions for rapid germination and growth.
Preparing the Garden for Late Summer Planting
Before planting new crops, gardeners must first clean up the spaces left bare by spent summer plants, removing debris and weeds to minimize potential pest and disease issues. The summer growing cycle often depletes soil nutrients, making August the perfect time to replenish the garden beds. Incorporating a two-inch layer of well-aged compost or other organic matter will improve soil structure, aeration, and fertility for the incoming fall crops.
Proper moisture management is important, especially when establishing tender seedlings in the residual summer heat. Deep, infrequent watering is preferred for mature plants as it encourages deeper, more robust root systems. Newly sown seeds and young transplants require consistent moisture in the top few inches of soil, often needing light, daily watering until their roots establish. Applying a thick layer of organic mulch, such as straw or wood chips, helps insulate the soil, keeping the root zone cooler and reducing water evaporation.
Heat mitigation is another consideration for August planting, particularly in areas receiving intense afternoon sun. Using a 40% to 50% light-blocking shade cloth can reduce the intensity of the sun’s rays and lower the soil temperature, which helps prevent delicate seedlings from bolting or succumbing to heat stress. Placing the cloth over new plantings provides a buffered environment for the first few weeks, ensuring a stronger start for the fall vegetables.
Cool-Season Vegetables to Start Now
August is the window for starting many cool-season vegetables that will thrive once daily high temperatures begin to moderate in the fall. These crops fall into two categories based on their preferred planting method: direct sowing or transplanting. Direct sowing is the easiest method for root vegetables and certain leafy greens, as they do not tolerate root disturbance well.
For direct sowing, gardeners should plant quick-maturing root crops like radishes and carrots directly into the prepared garden bed. Radishes can be planted every few weeks for a continuous harvest, while carrots require loose, well-drained soil to develop straight roots. Beets are another excellent choice for direct seeding, and both their roots and leafy tops are edible.
Certain leafy greens, including Swiss chard, spinach, and kale, can also be direct-sown in August, though they may require afternoon shade during the hottest weeks to prevent premature bolting. Bush beans are also suitable for August planting, as they are a warm-season crop that can still produce a quick harvest before the weather cools significantly.
Transplanting is the preferred strategy for brassicas, which require a longer lead time to reach maturity. Seeds for broccoli, cauliflower, cabbage, and Brussels sprouts should be started indoors or in a nursery area toward the beginning of August. These seedlings can be moved into the garden beds near the end of the month or in early September once they have developed several true leaves and the peak daytime heat has passed. Starting them early allows the plants to establish a strong root system while the soil is still warm, which is necessary before their winter harvest.
Herbs and Flowers for Fall Color
Beyond the main vegetable harvest, August is the time to ensure a continuous supply of fresh herbs and color that lasts through the mild Zone 9 winter. Many herbs that struggled in the summer heat can be successfully planted now to thrive in the cooler fall air. Cilantro and dill, which rapidly bolt in high temperatures, can be sown in succession throughout August and September for a steady supply of fresh foliage.
Parsley, a biennial herb, can also be started from seed or transplant in August, providing a harvest that will last well into the winter months. Cooler-weather mint varieties can be planted to establish themselves before the winter, but they should always be contained to prevent aggressive spreading throughout the garden beds. These herbs benefit from the transition away from the intense summer sun, resulting in more flavorful and abundant growth.
For ornamental color, gardeners can sow seeds for late-season flowers like marigolds and zinnias to ensure blooms continue into the autumn. These annuals are heat-tolerant and will provide a final flourish of color before the weather changes. Seeds or transplants of cool-season favorites like snapdragons and pansies should be planted in August. Pansies and violas tolerate light frosts, offering cheerful blooms even during the coldest periods of the Zone 9 winter.