Punch List: Which crops to cover on frosty nights; cover crops, cuttings from the garden (2024)

William Cullen Bryant, an insightful American poet and journalist, once said of this season, “Autumn…the year’s last, loveliest smile.” The fall season in Colorado is lovely, but also unpredictable. Warm, dry days can keep us busy outside doing our fall chores. Breathe it all in and enjoy the change of seasons, colors and chill in the air.

Frost

The nights have cooled down to the low 50s and dipped in the 40s. Light frost happens with temperatures around 32 degrees. Hard frost occurs below 28 degrees.The question is whether to protect your annual ornamental plants and vegetables or let them go.

Ornamental annual plants lose their will to bloom with cold nights. Replace them with cool hardy pansies, ornamental kale and mums for a fall blooming show.

Warm-season crops (tomatoes, peppers, tomatillos, eggplant, squash, beans, cucumbers, pumpkins, basil) need consistent 55 degree temperatures or higher to grow and ripen properly.

Semi-hardy cool-season crops (beets, carrots, Swiss chard, lettuce, cauliflower, potatoes, parsley) grow in minimum daytime temperatures of 40 degrees and higher. They cannot withstand hard frost without some kind of covering or protection.

Hardy cool-season crops (cabbage, broccoli, onions, radish, spinach, turnips, peas, and radish) grow in 40 degree daytime temperatures and can handle some frosty nights without protection.

To grow and produce well through the fall (or as long as you want to keep them going), both semi-hardy and hardy cool-season vegetables will need cold frames or covered tunnels.

Use lightweight sheets or the thickest floating row covers to cover when lower temperatures are predicted. Plastic transfers cold to the plant, so only use on top of row covers or sheets. Covers must extend over the entire plant and be secured to the ground to keep heat trapped inside. Be sure to remove covers the next day when it warms up.

If not covering harvest tomatoes prior to frost, look for mature green tomatoes (dull, light green in color) or ones that are beginning to develop color. Wrap each in newspaper until ripe, or simply place in a box (not touching each other) in a room with 65-70 degree temperatures. Light is not necessary for ripening, though some light will help with the color intensity.

Keep tomatoes away from a sunny window to ripen. They’ll get too hot and turn mushy.

Summer squash (zucchini, patty-pan or scallop, yellow straight or crookneck) and winter squash are warm-season crops and will not survive fall frosts.

Winter squash, which includes butternut, buttercup, hubbard, acorn, kabocha and many pumpkin varieties, are harvested when fully mature, and the fruit has developed a hard skin. This helps them store for many weeks in a cool, dry, dark place. A good indicator is to harvest winter squash and pumpkins when a fingernail cannot easily puncture the rind. Leave a 2-inch piece of stem attached to the fruit.

Cover crops or green manures

Both ornamental and vegetable gardens need optimal soil to support plant life. Optimal soil is fertile so plants have plenty of nutrients for blooms or fruit production, plus ample air and space to grow roots. Fall is a good time to improve it for next year.

Cover crops, also known as green manures, offer the one-stop planting answer to bring soil up to ideal standards. They also help keep soil erosion down during windy winter weather, along with reducing weeds and insect pests.

Legume seeds add nitrogen to the soil when they are tilled under and left to decompose. Look for Austrian winter peas or hairy vetch. Winter rye helps build and improve soil structure. Both seed types can be planted together. Direct seed them after clearing out spent vegetables or ornamental beds before it gets too cold (by mid-October) for seeds to germinate.

Look for cover crop seeds at garden centers or through mail order. Follow package instructions for seeding depth and area coverage. They will need some water to get established, but generally no care after that.

In early March, or when the soil isn’t too wet or frozen, cut down the growth low to the ground (it may not be very tall), then turn it over so it will break down for a few weeks before planting cool season crops.

In the landscape

Many outdoor ornamental annuals can be propagated from tip cuttings now and grown indoors for winter enjoyment. Plant them next spring. Try coleus, sweet potato vine, lantana, geranium, impatiens and begonia.

The key is taking cuttings before the plants freeze. Take a 4-inch cutting from a healthy branch, remove lower leaves and any flower buds. Dip in rooting hormone, then place in a container of perlite (or very light weight potting soil). Cover with a clean plastic bag to create a moisture dome until the plant roots, in just a few weeks. Additional tips: youtube.com/watch?v=QnSL4H_87dY

Plant seeds of quick-maturing cool-season vegetables: lettuce, spinach, arugula and other leafy greens, radish and short-rooted carrots. Tuck in seeds anywhere there is a bit of room, or use containers. Have cover cloths handy for cold nights.

Conifers, commonly known as evergreens (fir, spruce, pine, juniper and arborvitae), normally brown and shed older, interior leaves in late summer to fall. No cause for alarm. Read more: http://jeffcogardener.blogspot.com/2017/09/browning-evergreen-needles-normal-by.html