It might feel like an oven outside at times but the calendar doesn’t stop, the days are getting shorter, and it’s time to start planting your autumn garden. Autumn is a dream season for many cool-season vegetables including broccoli, kale, radishes, and salad greens, which are at their best when they mature in cool weather. But first you must get the seeds up and growing, which is not easy in high summer. Use these six tips for hot weather planting to get your autumn garden off to a strong start.
Chill Seeds in the Fridge
As soon as I start making autumn planting plans, I select seed packets from my main seed storage bin, put them in an airtight jar, and move them to the refrigerator. In the fridge it’s about 38°F (3°C), and cold temps are a gentle germination trigger for many dormant seeds. Some gardeners store all of their seeds in the refrigerator, but my seed collection takes up too much space. Yet I always use the fridge as a waiting room for seeds destined for the fall garden, reasoning that what seeds really want are conditions that mimic spring.
Prime Seeds Before Planting
Established seedlings are more heat tolerant than germinating seeds, which are very sensitive to high temperatures. You can get many seeds well on the road to sprouting by priming them in water prior to planting in prepared beds or containers. Priming is hugely beneficial with spinach seeds, and the procedure is simple. About a week before planting, soak seeds in room temperature water for 12 hours. Place the wet seeds on a paper towel, keep moist in a closed container, and allow to continue pre-sprouting for a day or two at room temperature. Plant as soon as possible.
To prime beetroot seeds, place your seeds in a jar, cover them with room temperature water, and drain off and replace the water every 30 minutes. After six changes of water, many of the natural germination inhibitors present in the seed coats are removed. Drain the primed beetroot seeds on paper towels overnight, and plant the next day. Primed beetroot seeds emerge in 4 to 5 days, compared to 7 to 12 days for dry seeds.
Start Slow Growers Indoors
Why take chances? When you need only a few plants, either start seeds indoors or buy your seedlings of cabbage, kohlrabi, even collards and kale. There is plenty of outdoor light to work with, so you should not need grow lights like you do in spring when the days are short and cold. As soon as seeds sprout, move them to a shady place outdoors, and transplant to the garden after they have more than four true leaves, or during a spell of auspicious weather.
Direct Sowing with Ice
One of the most creative hot weather planting tips ever, direct sowing with ice, comes from Pam Dawling, author of The Year Round Hoophouse and one of the most experienced gardeners I know. To get fast-germinating lettuce or radish seeds up and growing, chill the seeds in the refrigerator and then sow them in a nursery bed in the evening, topped or surrounded by a scattering of ice cubes or crushed ice. Cover with a shade cover, and add more ice or cold water the next day. The idea is to get the seeds actively germinating before they can be exposed to high heat, which can deepen seed dormancy. Should too many lettuce seedlings emerge, simply move some to a more spacious spot to mature. The direct sowing with ice method also works well with pak choi, coriander, and other fast sprouters, but is less effective with carrots and other vegetables that take several days to germinate.
Plant in a Paper Grid
To help maintain constant soil moisture after direct-seeding carrots, beetroot, radishes or turnips, try planting in a paper grid, which also reduces competition from weeds. Prepare the bed and rake it smooth, water well, then lay out strips of wet newspapers, 6 sheets thick. Plant seeds in the furrows between the paper strips, and cover with weed-free potting soil. The newspaper strips will slow surface evaporation, block light to weeds between the seeded rows, and make it easy to water and thin the little seedlings.
Use Shade Covers
Hot summer days sizzle a bit less when plants are protected with shade covers that filter out excess light. Even sun-loving plants appreciate a break, as do young seedlings that are just finding their feet. Don’t worry that plants are not getting enough light. When given relief from hot sun, shaded juvenile plants concentrate on growing extensive roots. When the weather moderates and you remove or lighten up on shade covers, the plants are raring to go.