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Aug 172012

Bulbs can be categorized into groups, based on growth characteristics or intended use, making selection easier. Useful groupings include season of bloom and hardiness.


Daffodils are among the favorite spring bulbs

Spring Flowering Bulbs

When considering bulbs, most people think of the common spring blooming flowers, including the crocus, daffodil, and tulip. These are plants that emerge relatively early in the spring, bloom for a short period of time, then die back and wait for next spring to repeat the process. These bulbs are usually hardy under most Idaho conditions and once planted need minimal care. Spring bulbs suitable for planting in Idaho include:

Common Name
Scientific Name
Relative Bloom Time
Regional Adaptation
Anemone Anemone Blanda Mid-spring N, SW, SC
Cammassia Cammassia leichtlinii Late spring N, SW, SC, SE
Chionodoxa Chionodoxa forbesii Early spring N, SW, SC, SE, HA
Crocus Crocus spp. Very early to mid-spring N, SW, SC, SE, HA
Daffodil Narcissus spp. Early to late spring N, SW, SC, SE, HA
Fritillaria Fritillaria spp. Mid-spring N, SW, SC, SE
Grape Hyacinth Muscari armeniacum Early to mid-spring N, SW, SC, SE, HA
Hyacinth Hyacithus orientalis Early spring N, SW, SC
Iris Iris spp. Late spring N, SW, SC, SE
Leucojum Leucojum aestivum Mid-springm N, SW, SC, SE
Ornamental Onion Allium spp. Late spring N, SW, SC, SE
Ornithogalum Ornithogalum umbellatum Late spring N, SW, SC
Pink Buttercups Oxalis adenophylla Late spring N, SW, SC
Puschkinia Puschkinia libanotica Mid-spring N, SW, SC, SE, HA
Snowdrops Galanthus nivalis Very early spring N, SW, SC, SE, HA
Squill scilla siberica Early to late spring N, SW, SC, SE, HA
Tulip Tulipa spp. Mid to late spring N, SW, SC, SE, HA
Trout Lily Erythronium spp. Mid-spring N, SW, SC, SE, HA
Winter Aconite Eranthis cilicium Very early spring N, SW, SC, SE, HA

Key to regional adaptation notes:
N = Northern Idaho valley locations in USDA zones 5 & 6, Moscow to Sandpoint.
SE = Southeastern Idaho valley locations in USDA zones 3 & 4 from Rexburg to Pocatello .
SC = South-central Idaho Magic Valley locations in USDA zones 4 & 5, Burley and Twin Falls .
SW = Southwestern Idaho Treasure Valley locations in USDA zones 5 & 6, Boise area (also Lewiston ).
HA = High altitude (>5,000 ft) areas of central, southeastern Idaho and similar locations elsewhere.


Many lily species grow well in Idaho

Summer Flowering Bulbs

Summer bulbs provide color after the spring flowers have stopped blooming. Many of them bridge the gap between spring bulbs and other perennials. Others bloom late into the summer. Summer bulbs are a mixture of those hardy in Idaho and those that are not hardy and must be treated as annuals. Non-hardy bulbs can be unearthed and stored for replanting the next year. Most of the tender summer bulbs are not recommended for planting in the shortest season areas of Idaho because of the potential for frost injury. For more information on storing tender bulbs overwinter, view this North Dakota Extension article.

Common Name
Scientific Name
Relative Bloom Time
Regional Adaptation
Bulbs Hardy in Idaho*
Arum Arum italicum Early Summer N, SW
Brodiaea Brodiaea laxa Early summer N, SW
Foxtail Lily Eremurus spp. Early summer N, SW, SC
Hardy Gladiolus Gladiolus nanus Mid-summer N, SW, SC, SE
Iris Iris spp. Early summer N, SW, SC, SE
Ixiolirion Ixiolirion pallasii Early summer N, SW, SC
Lily Lillium spp. Early to late summer N, SW, SC, SE
Ornamental Onion Alliums spp. Early summer N, SW, SC, SE
Ornithogalum Ornithogalum umbellatum Early summer N, SW, SC
Peonies Paeonia x hybrida Early summer N, SW, SC, SE, HA
Tender Summer Bulbs Grown as Annuals*
Begonia Begonia spp. Mid to late summer N, SW, SC, SE
Canna Canna spp. Late summer N, SW, SC, SE
Caladium Caladium spp. (colorful foliage) N, SW, SC, SE
Dahlia Dahlia spp. Mid-summer N, SW, SC, SE, HA
Gladiola Gladiolus spp. Early summer N, SW, SC, SE, HA

*Hardy summer bulbs can be planted permanently into the garden, tender bulbs must be handled like annuals with the bulbs being harvested and stored indoors during the winter months.

Key to regional adaptation notes:
N = Northern Idaho valley locations in USDA zones 5 & 6, Moscow to Sandpoint.
SE = Southeastern Idaho valley locations in USDA zones 3 & 4 from Rexburg to Pocatello .
SC = South-central Idaho Magic Valley locations in USDA zones 4 & 5, Burley and Twin Falls .
SW = Southwestern Idaho Treasure Valley locations in USDA zones 5 & 6, Boise area (also Lewiston ).
HA = High altitude (>5,000 ft) areas of central, southeastern Idaho and similar locations elsewhere.


Caladiums provide great summer foliage color

Fall Flowering Bulbs

A few bulbs bloom during the fall season. Those listed below are hardy in Idaho and include:

Common Name
Scientific Name
Relative Bloom Time
Regional Adaptation
Colchicum Colchicum autumnalis Late Fall N, SW, SC
Crocus (late types) Crocus spp. Late Fall N, SW, SC, SE
Hardy Cyclamen Cyclamen spp. Mid Fall N, SW, SC, SE
Lily Lillium spp. Mid Fall N, SW, SC, SE

Key to regional adaptation notes:
N = Northern Idaho valley locations in USDA zones 5 & 6, Moscow to Sandpoint.
SE = Southeastern Idaho valley locations in USDA zones 3 & 4 from Rexburg to Pocatello .
SC = South-central Idaho Magic Valley locations in USDA zones 4 & 5, Burley and Twin Falls .
SW = Southwestern Idaho Treasure Valley locations in USDA zones 5 & 6, Boise area (also Lewiston ).
HA = High altitude (>5,000 ft) areas of central, southeastern Idaho and similar locations elsewhere.


Some Crocus species bloom in the fall

The International Bulb Society has constructed a picture gallery that includes most of the worlds bulb propagated plants.

A fact sheet from North Carolina State University provides assistance with selection of bulb plants.

 August 17, 2012
Aug 172012

Proper site selection is critical for success with bulbs. The soil must be well-drained and attention given to proper light conditions (full sun for most bulbs).

Shovels in soil

Bulbs require deeply worked soil

Soil in bulb beds should be heavily amended with organic matter. Well-aged compost works well. Application of organic matter should be followed by deep tillage, at least 12 in. deep. The bed should be leveled and smoothed, but not packed. Just prior to or after planting, it is a good idea to add two or three inches of mulch (wood chips, bark, etc.) to the soil surface. It may also pay dividends to place some type of edging or border around the bed to slow encroachment of grass or other weeds.


Spring flowering bulbs should be planted in the fall. They require a period of cold weather to bloom and because these plants are generally hardy, the best way to provide cold is let them reside in the soil over winter. In Idaho , the best time to spring plant bulbs is late September through mid-October.

Summer flowering bulbs should generally be planted approximately one week after the last frost. To estimate the last frost date in your area, look at the Idaho chart compiled by Ed Hume Seeds. Some bulbs, such as caladiums and begonias will benefit from being started indoors 6-10 weeks before planting outdoors. They should not be taken outside until all danger of frost is past. In much of Idaho , this typically means 2-3 weeks after the last average frost date. Cornell University Suffolk County Extension has compiled a great discussion of planting and managing summer bulbs.

As a general rule, bulbs should be planted two to three times deeper than the top-to-bottom measurement of the bulb itself. Summer flowering bulbs may be exceptions to this rule and planting instructions should be provided on the purchase package. Planting density varies widely according to species and personal preference. Specific instructions for many species are provided in the Dutch Gardens web site. This site also provides pictures, descriptions, and cultivation techniques for many bulbs.

Before planting, an application of fertilizer should be made. Bonemeal or a high phosphate fertilizer should be placed in the planting hole, followed by the addition of a small amount of soil to prevent direct contact of the fertilizer and the bulb, then the bulb planted. This can be followed up with a small amount of a complete fertilizer (equal to 1 to 2 lb nitrogen per 1000 sq. ft.) at the time the plants emerge. Bonemeal should be used with caution around dogs, who are attracted to the scent and may dig up bulbs planted with bone meal.

Additional planting information can be found in sites sponsored by the Rochester Gardening Club and Iowa State University .

Bulbs are planted in the spring (for summer flowering) or fall (for spring flowering). Most bulbs are planted at least 4-8 inches deep, depending on the size. Fertilization at this time is recommended with a product high in phosphorus. Bone meal is an excellent choice,

Another excellent resource is the University of Illinois Bulbs and More web site.

 August 17, 2012
Aug 172012

There is a direct relationship between bulb size, bulb health, and flowering capacity during the first year or two after planting. Therefore, it is wise to purchase large, healthy bulbs from a reputable nursery. Success can be had by obtaining bulbs supplied by friends or neighbors if they are of adequate size and harvested from healthy plants. If the source is unknown, it is best to pass up the freebies for something of known value.

Do not purchase bulbs that seem very dry or shriveled. Also avoid bulbs that are soft or discolored. If purchasing bulbs sold several to a package, try to inspect each bulb. Try to avoid purchasing spring flowering bulbs like daffodils that have begun to sprout prematurely. In general, fresh, healthy bulbs should not have an odor. The exceptions to this are fritillaria bulbs, which have a distinctive, skunk-like smell.

Use care in handling some bulbs, such as hyacinth, which contain substances that can cause mild allergic reactions or skin irritations in some people.

Store bulbs in a cool, dark, dry location before planting. Try to plant your bulbs as soon after purchasing as possible.

 August 17, 2012
Aug 172012

Bulbs do not require and excessive amount of care, but timing and quantity of inputs are unique relative to other perennials. Here is a guide to care for established bulb gardens.


If not done before planting, it is beneficial to mulch the bulb flower bed before heat of summer sets in. This will keep the soil cool, retain moisture, and help with weed control.


Bulbs require deep watering


Bulbs have a range of water needs, depending on species, but most need soil that is consistently moist. For spring bulbs, except in the case of a very dry spring, irrigation is not usually needed until about the time flower buds appear on the plants. Once started, irrigation will likely be needed until the foliage dies and the bulbs go dormant. Because they are planted deep, bulbs should be irrigated less often and to a greater depth than nearby lawn areas. Summer flowering bulbs will likely need water until first frost.


Bulbs are not considered heavy feeders, but do need an annual application of fertilizer to look their best. Use a complete fertilizer that is relatively high in phosphorus. Apply the equivalent of 2-3 lb nitrogen per 1,000 sq.ft. Timing of application is fairly critical. Bulbs begin growing new roots very early in the spring and need fertility available to start this process. So, the best time to apply fertilizer to spring bulbs is in October or early November. A second option is to apply half the fertilizer in the fall and the other half about the time the plants begin to flower. Summer blooming bulbs do best with fertilizer applied about the time the plants emerge or when they are transplanted outside.

Weed Control

There are no options to completely replace hand weeding in bulbs. Mulching with organic matter or weed barriers will help by blocking germination and growth of weed seed. Perennial weeds that emerge before the bulbs can be sprayed out with a glyphosate product. Grasses in irises and gladiolas can be controlled with a grass herbicide containing sethoxydim. Grass controlling herbicides cannot be used on other bulbs without risk of serious injury.


Some bulb plants, especially summer bulbs, have large flowers and somewhat weak stems. They may need to be tied to stakes or allowed to grow inside a support cage to remain upright and attractive.


Foliage should die naturally before pruning

Post-bloom Care

Immediately after the bloom period, all seed heads should be removed. This not only improves appearance, but allows the plant to direct its energy to producing new and larger bulbs. The foliage of bulb plants should be allowed to die naturally (or at least be yellow and dying before removal). Healthy leaves are essential to the process of growing new bulbs. Over a period of a few years, removing the leaves too early will cause the bulbs to become smaller and decline in vigor.

Many gardeners do not like the look of post-bloom foliage in the garden. The unattractive leaves can be masked by planting other types of flowers in the bulb garden that will take up the slack in bloom time while the bulbs complete their growth and decline.

Over a period of several years, some bulb plants, such as daffodils, tulips, and crocuses will produce many bulbs and become crowded. When severe, this crowding will reduce bloom potential and make blooms smaller. This can be solved by uncovering the bulbs, dividing them into single units, and replanting the largest and healthiest of the bulbs at a more appropriate spacing. Dividing is best done in the fall, the usual time for planting bulbs. However, by fall all sign of foliage is gone and it is hard to identify the location of the bulbs. This can be solved by using small stakes to mark the plants before they die, or as a second best option, by simply dividing in late spring when the foliage has declined but still marks the presence of plants. Bulbs that are freshly dug and divided should be replanted as quickly as possible to prevent damage from drying conditions. Although not considered an option of choice in Idaho , spring bulbs can be harvested after blooming and stored in the refrigerator until being replanted in the fall.

Tender summer bulbs

Tender summer bulbs must be harvested and stored in the fall

In all regions of Idaho , the tender summer bulbs, such as dahlia, canna, tuberous begonia, and gladiolas must be harvested at the end of the growing season and stored indoors. Otherwise, the bulbs will be damaged or killed by freezing soil conditions. At the first sign of frost injury on the foliage, the bulbs should be harvested, cleaned, cured, and stored. Proper storage conditions vary by species. Complete discussion of the harvesting and storing process, including proper storage conditions for common summer bulb plants, can be found in a University of Minnesota document written by Mary Meyer.

The University of Illinois provides more general information on growing bulbs.

Forcing Bulbs

The term forcing refers to growing practices that bring bulb flowers into bloom during the off-season. Typically, this process is used to produce indoor flowers during the winter months. For each species, certain environmental constraints must be met to overcome bulb dormancy and allow growth and bloom. For spring bulbs, this usually means cold storage before planting in a pot. For summer bulbs, it may mean supplying specific requirements of light duration. It is beyond the scope of this discussion to provide specific requirements of all plants, but understand it can be done and seek procedures elsewhere. Information on forcing spring bulbs can be found on the University of Kentucky site.

Insect and Disease Control

It is beyond the scope of this site to provide specific pest management information for the large number of commercially available bulb species. Each has unique problems that may be more or less serious. However, there are many pests that are common and infest many types of plants. Diagnostic and simple control information will be given below for these common pests. For detailed information on control of insects and diseases, as well as information of other pests, see the Insect and Disease Pests section of this site.

Insect Problems

Aphids: Also known as plant lice. Small, soft-bodied, sucking insects that cluster on the stems or underside of leaves. Aphids are usually wingless and green, brown, or black in color. Symptoms of infested plants include distorted or curled leaves, presence of sticky sap (honeydew) on the infested surfaces, and misshapen new growth.

Aphids can be controlled with the use of insecticidal soap or a registered insecticide. A strong stream of water directed at the infected plants may knock them from the plant. Many beneficial insects feed on aphids and if an infestation is not too severe, it may be appropriate to be patient and let nature take its course.

Spider Mites: Not actually insects, these miniscule pests are actually related to spiders. They spin protective webs on the underside of leaves and feed by sucking juice from the leaves. Symptoms include color mottling that, at a distance, may appear as a general yellowing of older leaves. Webbing will be presence on the underside of infested leaves. The mites, to small to be easily visible, can be detected by shaking a leaf over piece of clean white paper.

Spider mites prefer dry, dusty environments. Sprinkler irrigation or routine washing of leaves with water usually keep them at bay. A severe infestation may require the use of a registered miticide. Most common insecticides are ineffective against spider mites.


Slugs can damage many bulb flowers

Slugs and Snails: Prefer damp soil and humid conditions. Slugs and snails often hide during the day and feed at night. Symptoms include chewed leafs and glistening slime trails on plant surfaces.

Control snails and slugs with baits.

Thrips: Damage is cause by the larva of this small, four-winged insect. Thrips reside on the underside of leaves and use their rasping mouthparts to scrape away the surface of the leaf after which they feed on the sap. Symptoms appear as white streaks and blotches, more prominent on the underside of the leaf.

A light infestation does little permanent damage to the plant and can be ignored. A heavy infestation will likely require the use of a registered insecticide.

Disease Problems

Root and Bulb Rots: Are caused by the penicillium (blue mold) and Fusarium fungi and the soft rot bacteria that live in the soil. These organisms are worse problems on bulbs that are harvested and stored than on those that are left in the soil over winter. Infected bulbs become soft, pink, or mushy and often have an offensive odor.

Control measures include careful harvesting to prevent injury that provides a point of entry for rot organisms. Infected bulbs should immediately be eliminated.

grey mold on peonies

Grey Mold affects many bulb plants, including peony

Grey Mold or Botrytis: Is caused by a fungus that overwinters in the soil. It infects plant stems that touch moist soil surfaces and splashed onto leafs with rain or irrigation water. Symptoms include water-soaked spots on the leaves that become a slimy, grey mold. Infected tissue quickly collapses and dies.

Control includes removal of infected tissue, both live and dead. In severe cases it may be necessary to apply a preventative fungicide.

Daffodils with virus

Bulb can be affected by chronic viruses

Virus: Not technically alive, viruses are small, disruptive pieces of genetic material that disrupt plant function. Symptoms vary widely and usually include some combination of stunting, yellowing, mottling, or leaf and stem distortion. Viruses are a particularly severe problem on bulbs and other perennials because their long life span and lack of seed propagation create many opportunities for chronic infection.

There are no control measures for viruses other than using resistant varieties or controlling the organisms (usually insects) that transfer them from one plant to another. Prevention involves removing and destroying any infected plants.

Information on control of garden insects and diseases common to Idaho can be found in the online Idaho Master Gardener Handbook.

See specific information on controlling bulb diseases and insects at the University of Connecticut web site.


Ornamental onions

Ornamental onions are eye-catching summer bulbs

 August 17, 2012