Jackie Bantle
Saskatchewan Perennial Society
Fall is a bittersweet time for gardeners. On one hand, all the hard work of the growing season is finally paying off with a delicious and varied harvest. Yet, there’s a definite chill in the air, signaling the end of the season and cooler temperatures to come. With the arrival of fall, there are still many tasks to complete to prepare our yards for the winter.
Not all plants respond equally to frost. Crops that must be harvested prior to a killing frost (0ºC) include cucumbers, beans, eggplant, lettuce, watermelon, peas, peppers, zucchini, tomato, cantaloupe and corn.
Onions are ready to harvest once their tops have fallen over. Stubborn onion tops can be “encouraged” to fall over by lightly stepping on them. Trim off the stems at the point at which they’re broken. Harvest them if frosts of -1ºC or lower are predicted, allowing them to cure in a warm location (20ºC) with good air movement for about one week.
Leeks can withstand a few degrees of frost and have a slightly sweeter flavour if they are exposed to cooler temperatures.
Cabbage can withstand up to 3 degrees of frost. Brussels sprouts benefit from several degrees of frost to encourage a sweet flavour and can withstand several hard frosts of -4 or -5ºC as long as they thaw during the day.
Root and tuber crops such as beets, carrots, rutabagas and potatoes should be left in the ground for at least one killing frost to improve their sweetness. As long as night temperatures do not dip below -4ºC and are above 8ºC during the day, the soil provides enough insulation to prevent the roots and tubers from freezing. To encourage potato tuber skins to set, the tops should either be dead or physically removed for at least one week prior to harvest.
Although winter squash and pumpkin vines freeze at 0ºC, the mature fruit can survive -4ºC. Once harvested, cure them indoors in a warm (20ºC) dry location. Long term storage in a slightly cooler, dry basement is recommended for pumpkins and winter squash. Green pumpkins can be ripened to orange in a warm, sunny, dry location.
In addition to harvesting vegetables, it is time to prepare trees and perennials for the winter season. Avoid fertilizing perennials, trees and shrubs in the late summer and early fall. Reduce irrigation during this time as well. Late applications of fertilizer and abundant water will encourage new, succulent growth which will not be winter hardy. After leaves have fallen and top growth has been killed due to frost, one last deep thorough watering of perennials, trees and shrubs is recommended just prior to freeze-up. Additionally, reduce lawn irrigation in the fall to slow grass down and prepare for cooler temperatures. Avoid applying fertilizer to lawns after Aug. 31.
Whether or not to cut back perennial plants after fall frost is up to a gardener’s preference. I like to keep any seed heads from my perennial plants intact over the winter in order to provide food for birds as well as some winter interest in the garden (ex. Karl Foerster grass waving above the winter snow). Some gardeners prefer to clean up the perennial bed prior to snow fall so that they are ready for new growth in spring. Plant debris can help collect snow, provide some protection for underground roots as well as a shelter for overwintering insects like lady bugs. On the other hand, if you had an insect problem in your garden this year, removing plant debris and working up the soil prior to freeze-up may help to kill some of the pests that are trying to overwinter in the garden soil.
Of course, as the leaves fall, it is a good idea to rake up leaves off the lawn prior to snowfall. Excess leaf material on the lawn overwinter can create a perfect environment for the growth of lawn snow mold. Use those extra leaves to protect your tender perennials or add to your compost.
If you have future plans to seed a new lawn or lay sod, fall is an excellent time to complete this task. Without the stress of hot, dry conditions, the sod will have an excellent chance of forming strong roots. Similarly, a newly seeded lawn will be easier to keep moist for quick seed germination in fall. As long as you are able to cut the new lawn at least once prior to freeze-up, the lawn seedlings should survive the winter without much damage.
Stay tuned for next week’s article when I discuss what trees and shrubs are best to prune in fall as well as moving perennials and fall planting.
Jackie Bantle is a horticulturist living in Saskatoon. This column is provided courtesy of the Saskatchewan Perennial Society (SPS; saskperennial@hotmail.com). Check our website (www.saskperennial.ca) or Facebook page (www.facebook.com/saskperennial) for a list of upcoming gardening events.
