General Concept - Flower bulbs selected for perennialization must receive several weeks of foliar senescence.  During this period, the mother bulbs either enlarge or are replaced by a daughter generation or offsets are produced.  The senescing foliage cannot be removed or bulb size will be markedly affected.  Therefore, the design plan must camouflage the effects of the dying foliage.

Fertilization

Spring Flowering Bulbs.  There are two fertilizer systems available.  The first system utilizes a single fall application at planting time of sulfur-coated, slow-release complete (9-9-6) fertilizer (Bulb Booster™).  This fertilizer should be incorporated into the rooting area at planting time at a rate of one rounded tablespoon per square foot.  The second system uses bone meal incorporated in the rooting area at planting time with an application of 8-8-8 (1 level tablespoon per square foot) or 10-10-10 (1 rounded teaspoon per square foot) in the fall followed by a repeat application of the same fertilizer as soon as the shoots break the ground in the spring.  Under perennializing conditions, all bulbs should receive annual fall applications of Bulb Booster™ or a soluble fertilization of 8-8-8 or 10-10-10.

Summer and Fall Flowering Bulbs.  Most of the summer and fall flowering bulbs should be fertilized monthly from shoot emergence until the plants reach full flower.  Subsequently, no fertilizers should be applied.  Usually 2 to 3 pounds of 8-8-8 per 100 square feet is adequate per application.  In addition, there are slow release materials, e.g., Bulb Booster™, which are also available and require only a single application.

Diseases - Although flower bulbs can become infected by a wide range of diseases (Moore, et al. 1979), most flower bulbs for perennialization have been selected for tolerance and/or resistance to most of the serious soil borne diseases. The most prevalent foliar disease that must be controlled in the landscape is Botrytis.  It is advisable to remove any heavily infested bulbs and to spray only when absolutely necessary.  Also, if plants are heavily infected with viruses, they should be removed.

Insects - There are several insects that can attack flowering bulbs.  Among them are: aphids, thrips, and mites.  Gardeners should always check their plants and be certain to correctly identify the insect prior to spraying with an insecticide.  Assistance for insect identification and the selection of the proper insecticide can be obtained from your local Extension Office.

Weed Management - (Reference:  Skroch and Derr, 1992.)  Weed management in established perennial plantings that include flowering bulbs and companion plants will require a combination of cultural, chemical, and mechanical weed control techniques.  Chemical weed control will require knowledge of both the weed and the ornamental species because herbicides are selective to control certain weed species.

In general, there are no postemergence herbicides that can be sprayed on bulb foliage without seriously damaging the plant.  Exceptions are Iris and Gladiolus, which are both tolerant of sethoxydim (Vantage™ and Poast™).

Preemergence herbicides, however offer more alternatives.  These herbicides are applied prior to weed seed emergence and there are several labeled for use with selected bulb species.  These include Betasan™, Devrinol™, Pennant™, Surflan™, and XL™.  HOWEVER, NO HERBICIDE SHOULD EVER BE USED IN A MIXED PLANTING UNLESS EVERY SPECIES IN THE PLANTING IS INCLUDED ON THE HERBICIDE LABEL INDICATING IT IS SAFE FOR THE SPECIES.

Since there is no general herbicide for all flower bulb and perennial species, glyphosate (Roundup™) remains the most versatile chemical for spot spraying to control perennial weeds in ornamentals.  For optimum control, use no more than 25 gallons of final spray solution per acre, apply only to dry plants, and allow at least 6 hours without rain or irrigation after application.  A 1% solution (1.25 ounces of Roundup 4L per gallon of water) will give excellent control of the target weed at the lowest  cost.  For some species, increasing the percentage to 1.5 or 2.0% is advisable.  One part glyphosate and two parts water can be used for wick applications.  Glyphosate is currently available as the active ingredient in many products.  The liquid products range from a 0.5% ready-to-use to concentrates of up to 53.8% active glyphosate.  There is also a dry flowable formulation that is 94% active ingredient.  Some of these products need a surfactant, some are ready-to-use.  Check each label for specific instructions.  A partial list of the glyphosate products include: Avail, Blot-Out, Blot-Out 2, Kleenup Grass and Weed Killer (RTU), Kleenup Spot Weed and Grass Killer, Systemic Weed and Grass Killer, Rodeo, Accord, Mirage, Rattler, Ranger, Honcho and Deploy Dry.

By taking advantage of periods of high and low susceptibility of ornamental plants and problem weeds, you can manage many difficult problems with this chemical.  In general, conifers and broadleaf evergreen shrubbery are most tolerant to glyphosate in late fall and early winter; whereas, small quantities will cause severe damage in the spring.  In contrast, deciduous plants are much more tolerant in winter, spring and early summer.  They can easily be damaged by glyphosate contact in the late summer and early fall when as few as six leaves on a 2 inch (5 cm) branch are sprayed with a 1% solution, death of the entire branch can occur.  The chart below has been developed based on this information.

  Optimum Application Rates and Timing of Glyphosate
 Weedy Species
Amount of Roundup™ 4L
Application Timing for Best Control
Perennial grasses 
(johnsongrass, fescue, quackgrass, etc.) 		1% At time of first flowering.
Bermudagrass 2% At time of first flowering.
Composites  
(asters, goldenrod, dogfennel, horseweed, etc.) 		1% At time of first flowering
Poison ivy 2 % Two weeks on either side of full flower (early summer).
Honeysuckle 1-1 1/2% Full flower up to a month after (early summer).
Kudzu 1-1/2 to 2% Full flower up to a month after (midsummer).
Blackberry 1-1 1/2% Fall and early winter.
Trumpetcreeper (cow-itch-vine) 1 1/2% Late summer to midfall before frost.

 

Animal Predation - Many flower bulbs, e.g., crocuses and tulips, are edible. Thus, animals such as voles, rabbits, and deer can devour them.  Therefore, their susceptibility must be considered when planning the garden.  When known, the susceptibility is provided for each bulb type covered in Part B.  Although no system can totally exclude animals, in some cases, covering the bulbs with heavy wire mesh screening that allows the shoots to grow through can afford some protection.