Gardening in Larimer County

Fall's the time to dig in and plant bulbs.  Tulips, crocus, hyacinths, muscari (grape hyacinths), snowdrops, Dutch irises, blue squill, glory-of-the-snow, daffodils and narcissi are some of the most common bulbs grown in Colorado.  Bulbs are easy to grow, requiring little attention.  They tolerate both sun and partial shade.  Spring-flowering bulbs add color to home landscapes earlier than annuals and most perennials.  Many bulbs will bloom and multiply for years without a great deal of care.

SELECTION

Buy spring-flowering bulbs as soon as they appear in the store.  Select the largest bulbs of any variety, because there is a direct correlation between bulb and flower size.  Avoid moldy, dry or damaged bulbs.  Bulbs individually selected from bins are preferable to those that have been prepackaged.  Loose bulbs may get mixed up by previous customers leaving you guessing at the varieties.

Most bulbs do best when planted in September and October.  Planting in early fall encourages early root growth and earlier spring flowering.  Bulbs planted after October may not have time to root adequately and may not flower the first spring.

WHERE TO PLANT BULBS

Flowering bulbs can bring attention to many areas in the garden.  Cluster them in flowerbeds, but also consider plantings around trees or in borders, window boxes or the lawn.  Select the site before purchasing bulbs.  If the bulbs are to remain in a location for more than one year, they will need adequate sunlight to regenerate strong bulbs.  Avoid southern exposure close to a foundation as the warmth near the foundation can force bulbs to leaf out early resulting in injury from freezing temperatures.

SOIL PREPARATION

Dig the bed to recommended depths.  Planting depths are in relation to the size of the bulbs.  Apply fertilizer and soil amendments at this level, and spade or rototill the soil to a depth of about 4 inches.  For fertilizer to be effective, it must be present in the vicinity of the roots.

The flower bud and the food necessary to produce the flower are already present inside a bulb when it is planted.  However, fertilizer promotes larger bulbs and improves the following year’s flower growth.  When spading the bed, mix in phosphorus with the soil at a rate of 1/2 pound of 0-46-0 fertilizer (super phosphate) per 100 square feet.

Before soil is shoveled back into the bed, mix it with some type of organic matter (peat moss or well-decomposed compost) to improve the texture of high clay content soil.  Amended soil offers less resistance to the bulb’s shoot as it emerges and provides better aeration and drainage for root growth.

PLANTING AND GROWING FALL BULBS

Space the bulbs as recommended or as desired and return the soil and the water to settle it around the bulbs.  As a general rule, the depth from the soil surface to the top of the bulb is four times the height of the bulb.  Be sure bulbs rest firmly in the soil, without any air space under the bulb.

Plant bulbs with the growing tip up.  After the ground freezes, cover the bed with three inches of mulch to prevent alternate freezing and thawing that can break roots and damage bulbs.  This mulch can be removed in April before the shoots emerge, or left in place if the shoots can emerge easily.  Remove flowers as soon as they whither, since seed production diverts food that otherwise would be used to produce more vigorous bulbs.  Apply nitrogen at the rate of 1/4 pound per 100 square feet before the foliage withers.  The bed usually is not dug up after the first year.  After the second year, the developing bulbs may lose much of their original vigor.  When this occurs, dig the bulbs in late August and allow them to dry for a few days in a shady, cool spot.  Divide and replant only the best ones, preferably in a new location.  If none of the bulbs is as large as the original ones, purchase new bulbs for better results.  Also it is possible to interplant annuals among the withering bulb tops.  However, do not remove the bulb tops until they are dead.( Note: lilies normally are planted in the spring, while autumn crocuses are planted in midsummer.)

Fall bulb planting can be done with a master design or with total abandon.  Solid blocks of single colors can be seen more easily from a distance than mixtures of colors and varieties.  Many gardeners, however, plant bulbs with no plan or organized scheme.  With attention to peak bloom time of specific varieties, either method can offer successive waves of welcome spring color.

For more information on planting bulbs, see Fact Sheet #7.410 - Fall planted bulbs and corms.

Q:  What is the difference between pruning and shearing?

A:  There is a big difference between pruning and shearing.  The purpose of pruning is to modify the plant’s growth for any of the following reasons: to maintain plant health by removing diseased, dead or injured limbs or stems; to control or direct growth and to increase the quality or yield of fruit or flowers.  Good pruning techniques always take the response of the plant into consideration by making cuts that improve the plant’s health. If you remove growth continually to control size, the result is shearing, not pruning.

Shearing is the process that maintains the even surfaces of formal hedges and topiaried plants.  Plants normally used for these purposes are specifically chosen because they have buds and branches that are close together on stems.  After shearing, the fresh cut is close to a new growing point.  Shearing can result in geometric plantings that compliment architectural forms.  However, because it indiscriminately levels out bud growth, certain plants can be weakened.

Shearing a hedge, while attaining a desirable visual effect in a formal setting, may over time, result in weaker, shaded-out plants which will require occasional thinning.  Choose the appropriate plant if you are planning a formal hedge.

Q:  What about grasshoppers?

A:  Grasshoppers are common invaders in Colorado yards and gardens and are among the most difficult pests to control.  Grasshopper problems tend to increase as summer progresses and usually continue even after the first frost.  Grasshoppers favor feeding on such vegetables as lettuce, carrots and onions.  They tend to avoid other vegetables such as squash, peas and tomatoes (leaves, not fruit).  Among the shrubs and trees damaged by grasshoppers, conifers usually are avoided.  However, during years when grasshoppers are extremely abundant and food is scarce, they feed on almost all plants.  Established trees and shrubs tolerate this leaf loss and usually recover and suffer little long-term injury.

Consider having your soil tested in the fall so you can fertilize while the weather is good and have the soil prepared for spring planting.  When taking soil samples, do not use galvanized or brass equipment, as the soil will be contaminated.  Tools must also be clean and free of rust.  Make sure to air dry your soil samples within 12 hours.  This will give a better nitrogen reading.  Water, plants and manure can also be tested.

Think now about mulching flowerbeds for the winter.  Mulch can be used to protect fall transplants by moderating temperatures and allowing more root growth.  This will protect shallow rooted plants and bulbs from frost heave.  Some mulch including straw and loose leaves can become favorite places for rodents.  Place these mulches at least 6 inches from the base of woody plants to prevent chewing damage to the bark.

The authors have received training through Colorado State University Cooperative Extension's Master Gardener program and is a Master Gardener volunteer for Larimer County.

Gardening and Insect Fact Sheets are available on-line by clicking HERE.

Return to Master Gardener Articles

This page updated:  March 28, 2003