To me, fall is the best time of year to plant in Colorado. Besides the fact that it’s easier on me to plant when the temperatures are mild, it’s also easier for the plant to get established after the blistering heat has ended and before harsh, winter weather arrives. Last of all, fall is a great time to find still-healthy plants on sale, if you have some time to shop around and select carefully.
By Susan Perry
Colorado State University Extension Master Gardener in Larimer County
Sometimes, “fall” starts in Colorado in mid-August and can often last till mid-November. By “fall”, I mean the really hot weather has broken, the temperatures are in the low 80s, and the ground can still be dug. Mornings are cool and crisp, and it’s a pleasure to be outside gardening. Even if you garden into the afternoon, the temperatures are mild enough to prevent you and your plants from wilting. For trees, shrubs, sod, and perennials, try to start your planting as early as possible, to give plants the chance to establish roots before the ground freezes. Waiting until late October or early November will reduce the chance that your plants will survive.
While some plants prefer spring planting, either because they require more regular moisture than one can expect during a typical Colorado winter or because they need heat to develop their root system, they are the exception. This is not to say that they will die if planted in the fall, but simply that the chance they’ll survive are higher if planted in the spring. Plants preferring spring planting include ornamental grasses (particularly warm-season grasses), evergreens, hostas, astilbe, clematis vine, whirling butterflies (Gaura ‘Siskiyou Pink’), buddleia, some ice plants and other succulents, raspberries, some penstemons, agastache, and evening primrose (Oenothera speciosus ‘Rosea’).
For the most part, fall planting is easier on the plant. Since the flowering and budding season is over, the plant will concentrate all its energy on developing a root system. In the fall, the soil is still warm which also encourages the plant to establish roots. By the time we get harsh, freezing weather or significant snow, your fall plantings may have had several months to establish. Without the stress of extreme heat, plants have a longer period to establish and expand their roots systems. As long as the soil temperature remains above 40 degrees, root growth can continue. The earlier you can get started, the longer head-start you give the plants. Just be sure to mulch thoroughly after planting, both to increase moisture retention and to provide winter protection.
Also, be sure to give your plants adequate water throughout the fall. Once winter comes, plan to water at least monthly, early on a sunny day when the temperature is above freezing. Unless we have extended periods of snow, without regular winter watering, our relentless winter winds can desiccate your new plants, which may appear normal in spring but then suddenly succumb to summer heat or other stress-related problems. Finally, be cautious about fertilizing fall plantings: many fertilizers are high in nitrogen, which will promote foliage growth at the expense of root development. It’s better to err on the side of caution when contemplating fertilizing fall plantings. With the proper care, by spring your plants will bloom as if they were multi-year veterans in your garden.
Finally, most nurseries want to clear out as much of their stock as possible in the fall so that they don’t have to spend the winter keeping their plants alive. While the selection of plants available in inventory in the fall may be limited, if you’re flexible about what plants you want, there are great deals available. As time passes, the prices go lower and lower. You simply have to weigh the chances that waiting late enough to get a great price will risk that there’s not enough time for the plant to establish before the ground freezes. Or, as Clint Eastwood famously said, “Do you feel lucky?”
One year, I bought a honeysuckle in late October for $5 that was originally priced at $25 in May. The following spring, it looked like a champ and anyway, I figured if it didn’t live, I wasn’t breaking the bank. That time, it worked out. Other times, it hasn’t. Either way, look carefully at the plant to make sure it’s healthy, but I’m a big believer that healthy roots are most important. Even plants with dead foliage can grow into beautiful specimens, as long as they have healthy roots, are planted correctly, and given a little TLC.
In my opinion, fall planting can be quite successful in Colorado. With the proper selection of plants, enough time for them to become established, and proper winter care, you can get a head-start on a beautiful garden for next spring.