The August gardening calendar represents a transition from the intense heat of summer to the productive, cooler fall season in Missouri. This period is the final opportunity to sow seeds and set out transplants that will mature before the first widespread frost. By strategically planting cool-weather crops now, you can extend your harvest well into October and even November. Success requires careful selection of varieties and a proactive approach to managing the residual August heat. Planning for a fall garden allows you to capitalize on the mild temperatures and shorter days that concentrate flavor in many vegetables.
Fast-Growing Leafy Greens and Herbs
Loose-leaf lettuce varieties, such as Black Seeded Simpson, can be ready for a first harvest in as little as 30 days. Arugula and radishes typically mature within 21 to 40 days. These short maturity windows allow for multiple plantings before the season ends. Radishes, while technically a root crop, are included here due to their rapid 3-4 week growth cycle.
To ensure a continuous supply, employ succession planting by sowing a new, small batch of seeds every two to three weeks. Spinach and cool-season herbs like cilantro and dill should also be sown in August; spinach is very frost-tolerant and often withstands light freezes. Spinach germination can be improved by pre-chilling the seeds in a refrigerator for a week before planting. Harvesting the outer leaves of lettuce and spinach (the “cut-and-come-again” method) rather than the whole plant encourages prolonged production.
Root Crops for Late-Season Harvesting
Root vegetables planted in August benefit from a natural biological process that enhances their flavor as temperatures drop. Carrots, beets, and turnips are excellent choices for a fall harvest, but they must be sown directly from seed in the garden. These crops require a slightly longer maturation time, often ranging from 50 to 70 days, allowing them to fully develop before the hard freeze.
The cooling soil temperatures trigger a process called cold-sweetening, which significantly improves the taste of these vegetables. As temperatures fall below approximately 41 degrees Fahrenheit, the plant converts its stored starches into simple sugars. This sugar acts as a natural antifreeze, lowering the freezing point of the water within the plant’s cells to protect them from frost damage. Ensuring a loose, well-drained soil is important for root crops, as compacted soil can lead to stunted or forked roots.
Brassicas and Fall Transplants
Broccoli, cabbage, cauliflower, and kohlrabi require a longer growing season, making August the ideal time to set out transplants. Starting with four to six-week-old transplants bypasses the challenges of seed germination in hot soil and ensures the plants have enough time to form heads or florets before the killing frost. These crops need approximately 60 to 85 days to reach maturity from transplanting.
The warm August weather can make these crops vulnerable to pests, particularly the “cabbageworm complex.” These pests feed voraciously on the foliage and bore into the heads of the developing vegetables. To manage these insects, gardeners can apply a biological insecticide containing Bacillus thuringiensis (Bt), which is safe for beneficial insects but toxic to the caterpillars upon ingestion. Covering the plants with a fine mesh floating row cover immediately after transplanting can also provide a physical barrier against the egg-laying adult moths and butterflies.
Timing and Soil Preparation
Successful August planting in Missouri relies heavily on calculating the final safe planting date backward from the average first frost. In Northern Missouri, this median date for a 32°F freeze typically falls around the second week of October, while central Missouri is closer to the third week, and the Bootheel region often sees it in late October or early November. You must add the crop’s “days to maturity” (DTM) plus an extra two weeks to account for slower growth in the shorter, less intense light of fall.
High soil temperatures, often exceeding 80°F, can inhibit the germination of many cool-season seeds like spinach and lettuce. To combat this, plant seeds slightly deeper than recommended on the packet to access cooler, moister soil. Consistent moisture is also necessary, and a temporary shade cloth placed over the rows during the hottest part of the afternoon can lower the surface temperature and reduce moisture evaporation.
The soil requires amendment to support the fast growth needed for a fall harvest. Incorporating a two-inch layer of well-aged compost into the top few inches of soil replenishes organic matter and improves water retention. Unlike spring planting, where nitrogen fertilizer is often applied early, the focus for fall should be on balancing nutrients and ensuring excellent soil structure to encourage rapid, healthy root and leaf development. Regular watering is essential until the cooler fall rains begin to provide consistent moisture.