TLC for Tender Bulbs
By: Anne Wuerslin
Colorado State University Extension Master Gardener in Larimer County
When leaves fall and frost arrives, the garden goes to sleep. We usually consider fall a time for planting spring-flowering bulbs such as tulips and daffodils, which can overwinter in the ground. But, part of garden clean-up is to dig tender bulbs, tubers, corms and rhizomes and put them in proper storage, as our Colorado winter temperatures are too cold for their survival. Often what was planted in the spring will have multiplied, and next season, you’ll have more blooms at fraction of the price.
Botanically speaking, a true bulb is a collection of leafy scales and contains the growing point of the plant in the center. Corms (gladioli, crocus) are solid, modified stems with a tunic sheath. They replace themselves yearly by growing new corms or side cormels on top of the old. Tubers (dahlias, tuberous begonias) are thickened stems which grow larger and larger each season, usually from an underground leading point called an eye. Rhizomes (iris, lily of the valley, cannas) are modified swollen stems which have adapted to lie and grow parallel to the soil surface. They multiply season to season, sending out growing stems at intervals to the surface.
Gladioli corms should be dug up before a true hard frost. Cut the sword-like foliage down to one inch above the parent corm, shake off the soil, and let air dry for one to two weeks, out of the sun (a garage or basement works well). Gently separate the original corm and discard; keep new corms and place them in paper bags. You may want to label the bloom colors on the bag. Some moth flakes in the bags will help prevent against thrips overwintering, if this was a problem in your garden. Store the bagged corms in a cool basement or garage, at 40-50 degrees F. Hardy crocus corms can stay in the ground for winter; they tend to clump, due to new corm growth next to old, creating a more spectacular bloom show in spring.
Wait for the foliage to blacken from frost before digging up dahlia tubers. Use a garden fork or small spade, taking care not to slice into the tubers or break off the necks which are attached to the crown of the plant. Cut off dead foliage and stems to about two inches, turn over and drain out any water from the hollow stem. Let superficial soil remain and do not wash tubers—this will prevent excessive drying out and shriveling during the winter. Label the color and varieties of the dahlias. Store stem side up in a darkened cool box which can be lined with black plastic and filled with sawdust, vermiculite, or peat moss (do not use garden soil). Take care not to let the tubers dehydrate. Storage should be cool and somewhat damp, around 35-45 degrees, always above freezing. In March, replant indoors for a head start on summer growth or wait until the last frost has passed in spring, around May 15, and plant in the ground.
Tuberous begonias, as well as caladium tubers, can be dug after a light frost when the foliage turns brown. Take the stems with some soil and air dry for one to two weeks. At this time, the stems should separate from the tuber. Shake off any remaining soil and store in bags (paper or perforated plastic) with peat moss, perlite or dry vermiculite, and store like gladioli corms. They can be potted up indoors in February for eventual placement outdoors after danger of frost has passed.
These summer-blooming bulbs are show-stoppers in the garden, and will bloom reliably year-after-year. For more information on summer-blooming bulbs, visit the CSU Extension website at www.ext.colostate.edu and read Fact Sheet #7.411.
By: Mitzi Davis
Colorado State University Extension Master Gardener in Larimer County
Fall is an excellent time for taking soil samples from your lawn and garden. Soil tests will measure the pH of the soil, organic matter content, and salinity. The test will also measure plant available nutrients such as nitrogen, phosphorus, potassium, iron, zinc, manganese and copper and give suggestions to improve your soil. Testing kits for the CSU Plant, Soil and Water testing laboratory are available at local nurseries, Jax Farm and Ranch or the Larimer County Extension office, 1525 Blue Spruce Drive in Fort Collins. You can also call the Extension Office at (970) 498-6000 for more information.
Overwinter your geraniums inside to get a head start next spring. You can cut them back to half the original size and repot them in potting mix rather than garden soil. Check for insects or disease. Grow in a cool room with plenty of bright, direct sunlight. You can also take cuttings from your plants. Make 3-4” long stem cuttings that include a growing tip. Remove the lower leaves, dip the cut end in rooting hormone and stick into moist, porous, rooting medium. It will take six to eight weeks to root. After rooting, plant geraniums in 4” pot in a sunny window.
You should wait until spring to prune your roses, but keep some soil or mulch handy to mound around your roses for winter protection. Wait until the leaves drop and the ground is near freezing, usually late November or early December before covering the base of the plant.
Strawberries need protection from our drying winds, intense sunlight and lack of moisture during winter. Apply mulch after the plants are dormant, but before nighttime temperatures drop to 20 degrees F. You can use organic mulch, like straw, or you can cover the bed with a heavy weight “floating” row cover.
By: Beth Thiret
Colorado State University Extension Master Gardener Volunteer for Larimer County
Q: Why do I need to water my plants in the winter?
A: In Colorado, we are known for our dry air and fluctuating winter temperatures. This can cause damage to a plant’s root system. The end result is plants more susceptible to insect and disease problems or dieback. Water your plants when the temperatures are about 40 degrees F and there is no snow cover. When water is applied at mid-day there will be ample time for it to soak in before freezing at night. For more information on winter watering refer to the CSU Extension website at www.ext.colostate.edu and read Fact Sheet #7.211.
Q: Why are some tree trunks wrapped in paper during the winter?
A: The intention of winter tree wrap is to protect the trunks of younger/newly planted trees from the temperature fluctuations we get throughout fall and winter months. Warm winter days, followed by freezing night temperatures and winter drought, can result in sunscald and frost cracks. However, research has shown that wrapping the trunks and leaving the wrap on too long can also cause harm to trees by allowing excess moisture to remain in contact with the tree, encouraging fungal and bacterial growth. Trees planted in locations receiving a lot of reflective light may still benefit from its use. Around the end of November, using a light crepe paper wrap, wrap the trunk up to its lowest branch, check the tree frequently throughout the winter and remove the paper wrap in the spring in late March or early April. A good rule of thumb to remember when to put the wrap on and take it off is: on at Thanksgiving; off on Tax Day.
The authors have received training through Colorado State University Extension’s Master Gardener program and are Master Gardener volunteers for Larimer County.
Larimer County is a county-based outreach of Colorado State University Extension providing information you can trust to deal with current issues in agriculture, horticulture, nutrition and food safety, 4-H, small acreage, money management and parenting. For more information about CSU Extension, Larimer County, telephone (970) 498-6000 or visit www.larimer.org/ext
Visit PlantTalk Colorado ™ for fast answers to your gardening questions: www.planttalk.org PlantTalk is a cooperation between Colorado State University Extension, GreenCo and Denver Botanic Gardens. PlantTalk is also on Youtube!