August in Ontario marks a significant transition in the gardening year, shifting focus toward succession planting for a bountiful autumn and winter harvest. This period requires gardeners to strategically select crops that can mature before the inevitable arrival of the first hard frost. Planning now allows for the continuous production of fresh vegetables while simultaneously laying the groundwork for next spring’s earliest yields.
Understanding Ontario’s Late-Season Gardening Window
Successful fall gardening in Ontario depends on understanding the local climate, which spans hardiness zones from 3 in the north to 7 in the south. Gardeners must identify their specific zone to gauge the length of their remaining growing season and calculate their average first frost date. Southern Ontario often sees its first frost between late September and late October, while Northern regions can experience it as early as late August.
The key calculation for August planting involves a crop’s Days to Maturity (DTM) listed on the seed packet. Select varieties whose DTM is significantly shorter than the number of days remaining until your average first frost. Because the days are shortening and the sun’s intensity is decreasing, plant growth naturally slows down. Subtract at least two weeks from the stated DTM to account for this reduced growth rate, ensuring the harvest occurs before a killing frost.
Vegetables and Herbs for a Quick Fall Harvest
Leafy greens are the backbone of the August-planted fall garden, as they are highly cold-tolerant and mature quickly. Spinach, kale, and Swiss chard are excellent choices, often improving in flavor after a light frost converts starches into sugars within their leaves. Slower-to-bolt lettuce varieties, like butterhead or romaine, thrive in the cooling temperatures that prevent the bitterness caused by summer heat. For a continuous supply, sow a new batch of seeds every two weeks, a technique known as succession planting.
Quick-maturing root vegetables also perform well when sown in early August, rewarding the gardener with a harvest in 30 to 75 days. Radishes are the fastest, often ready in under a month, making them perfect for filling small gaps in the garden. Baby carrots and beets require slightly longer, typically 60 to 75 days, but their roots sweeten considerably after exposure to cold. Ensure the soil is loose and free of stones, as compacted earth can lead to misshapen or forked roots, particularly in carrots.
Other quick-turnaround crops, such as bush beans, can be sown very early in August in the warmer southern zones, though they are more susceptible to frost than greens. Kohlrabi, a fast-growing brassica, and certain herbs like cilantro and dill thrive when planted now. Cilantro and dill will produce fresh foliage until a heavy frost, benefiting from the cooling days.
Since August still brings periods of intense heat, proper soil management is essential to prevent premature bolting in young plants. Amending spent beds with fresh compost replenishes nutrients for the new seedlings. Consistent and even watering is necessary during germination and early growth to keep the soil surface cool and moist, which discourages leafy greens from flowering and going to seed.
Planting Now for Next Spring’s Yield
August is the time to prepare the garden for the following year, starting with the planning and ordering of spring-flowering bulbs. While the actual planting of tulips, daffodils, and crocuses usually peaks in October, securing desired varieties in August ensures availability. The bulbs are ready to be planted once the soil temperatures have cooled down.
Garlic is another crop that requires an early start for a successful summer harvest, needing a period of cold exposure, or vernalization, to properly form cloves. Hardneck varieties are the most common and cold-hardy types grown in Ontario. Planting individual cloves in late September through October allows enough time for the root systems to establish before the ground freezes solid.
For ornamental areas, planting cool-season perennials and biennials, such as foxglove or certain daisies, in late summer allows their root systems to become well-anchored before winter dormancy. A robust root system increases the plant’s chances of surviving the winter and emerging healthy in the spring.
Gardeners can also sow cool-season cover crops, like clover, oats, or winter rye, in any beds that have been harvested and cleared. These crops are grown to improve soil health by preventing erosion and adding organic matter. Nitrogen-fixing legumes, such as clover or vetch, also replenish the soil with nitrogen, benefiting the heavy feeders planted there next spring.