Top "Ten +1" Reasons Why Flowering Plants Fail To Bloom

1. Maturity	7. Temperature
2. Light	8. Planting Depth
3. Excess Nitrogen	9. Root Environment
4. Pruning	10. Alternate Flowering
5. Severe winters and late spring frosts	11. Overall Health
6. Deadheading	PHOTOS

1. Maturity

Flowering plants typically undergo a juvenile period before they begin to produce flowers. During this juvenile period, the plant produces stems and leaves but no flowers. The plants will not produce flowers (reproductive structures) until they are mature. The juvenile period can range from weeks in annual plants to years in woody plants, depending on the species and cultivar in question. Because annual plants complete their life cycle in one growing season, they undergo a relatively short juvenile period before flowering. Biennial plants complete their life cycle in two years. The first year yields only vegetative growth and the second year yields flowers and seeds. Perennial plants have one vegetative year followed by repeated flowering years. The juvenile period can last for years in woody ornamentals and fruit trees. Markets now favor the production of certain dwarf apple trees that have a reduced juvenile period. These dwarf plants may mature up to five years earlier than a standard apple and will, therefore, produce flowers and fruits sooner. Even flowering houseplants may undergo a juvenile period before flowering. A bird-of-paradise plant, for example, will not bloom until it is at least four or five years old. If the flowering plant in question has never bloomed before but appears to be quite healthy, immaturity may be a probable cause. On the other hand, a plant that has bloomed beautifully in the past but lately is producing only small, weak flowers may simply be exhibiting signs of old age. This type of decline occurs quite frequently in herbaceous perennials. Dividing old perennials and advancing only the youngest plantlets will usually encourage a healthy and vibrant floral display. Even hardy bulbs such as daffodils may decline with age. In this situation, it may be easier to simply plant new bulbs.

2. Light

All plants have preferences when it comes to light exposure and all flowering plants have minimum light requirements necessary for flower production. Lilacs, for example, require a minimum of six hours of full sun daily in order to produce a good show of flowers. If shade is a problem in the garden, select herbaceous and woody plants that will adapt to and flower in reduce light conditions. It is important to realize, however, that even shade plants require at least few hours of morning sunlight (or dappled sunlight throughout the day) in order to set flowers. This is one of the principle reasons why it can be impossible to grow turf and other plants beneath large trees. Most plants cannot even survive in severe dense shade, let alone set flowers. Insufficient sunlight is often a huge problem with flowering houseplants and may warrant a supplement of artificial light. Plants that exhibit spindly growth and yellowish leaves are likely deprived of adequate light.

Many plants flower in response to photoperiod, which is essentially daylength. For these plants, the flowering process is triggered when a minimum light/dark requirement is met. Long day (short night) plants flower in response to increasing daylength. Examples of long day plants include delphinium and coneflower. Short day (long night) plants flower in response to decreasing daylength. Examples of short day plants include chrysanthemum and poinsettia. Day neutral plants do not flower in response to photoperiod; they simply flower when they are mature. Examples include geraniums, pansies and certain strawberries. If plants fail to bloom, it could simply be that it is the wrong time if year. Indoor plants can be induced to flower by manipulating photoperiod using artificial light or dark treatments. This is how growers ensure that poinsettias are flowering in time for Christmas and lilies in time for Easter. If using artificial light to remedy inadequate sunshine, it is important to realize that this interferes with photoperiod and may inhibit the flowering process in certain houseplants.

3. Excess Nitrogen

A plant that is grown in the correct exposure and exhibits healthy, green, vigorous growth but fails to set flowers could be subject to excess soil nitrogen. Excess nitrogen in the soil promotes a flush of green, vegetative growth at the expense of flowers. Flowering is essentially delayed or inhibited by the continuous production of new leaves and stems. It is one of the leading causes of poor fruit production. No flowers means no fruit. The effect of excess nitrogen on flowering is commonly seen in trees and shrubs that inhabit lawns or other grassy areas. High nitrogen fertilizers are applied to turf in order to encourage lush, green, vegetative growth. Although desirable for grasses and other foliage plants, nitrogen applications tend to have an adverse effect on flowering plants. A possible remedy is to water deeply and thoroughly to flush away the excess nitrogen and fertilize later with a high phosphorus or high potash formula. In fact, most tomato foods are ideal for fertilizing flowering plants. A related but opposite scenario, nutrient deficiency can also contribute to poor flowering. Nutrient deficiency is quite common in containerized plants whereby the roots have only a limited amount of soil area in which to explore and draw nutrients from. The nutrients inside containers are depleted rapidly and need to be replenished on a regular basis in order to maximize bloom time and flower quality.

4. Pruning

Improper pruning techniques are frequently responsible for poor flowering, particularly in woody plant species. Pruning a plant at the wrong time of year can result in the actual removal of flower buds. Simply put, if the flower buds are removed, the plant will not flower. This type of pruning error is common in spring flowering shrubs such as lilac and forsythia. Spring flowering shrubs typically flower on last year's wood. If they are pruned in fall, late winter, or even early spring, the flower buds will be removed. If this happens, there will be no flowers in the following spring. Winter-feeding animals can actually remove the flower buds, creating the same outcome. A good time to prune spring flowering shrubs is immediately after flowering, before they have had a chance to set next year's buds. Summer flowering shrubs typically bloom on current year's wood. These should be pruned after flowering or in the winter but not after new growth has begun. Excessive pruning can also have a negative effect on flowering in the same way that excess nitrogen can. Heavy pruning stimulates a flush of vegetative growth that, in turn, delays or inhibits flowering.

Hardy bulbs are also common victims of pruning mistakes. Even though the flowers may fade early in the spring, the foliage must be maintained throughout the growing season in order for the bulb to accumulate enough food to support next year's growth. Many gardeners think that the foliage is an unsightly nuisance and will cut it back prematurely. In some cases, lawnmowers or other garden equipment remove the leaves accidentally. Failure to allow the foliage to die back naturally jeopardizes the success of next year's floral display.

5. Severe Winters and Late Spring Frosts

Prairie winters are typically characterized by extremely low temperatures and little snowfall. Severely cold winters without adequate snow cover can challenge even the hardiest plants. Perennials with only marginal hardiness often succumb to such winter conditions and fail to come back the following spring. Spring flowering shrubs such as forsythia produce flowers on year old wood, meaning that the flower buds are set prior to winter. Without adequate snow cover, these flower buds are extremely susceptible to winter injury and may fail to bloom in the spring. In this situation, the dead buds often remain on the plant, making it easier to identify winter injury as the cause. It is not uncommon for only the lower portion of a shrub to flower in the spring. In this case, higher buds exposed to the elements are killed but lower buds insulated by snow are able to survive. If winter injury has affected the bloom on one plant, it has likely affected other plants of the same type. Ask friends and neighbours if they have experienced a similar problem. If you seem to be the only gardener without lilacs, winter injury is perhaps not the problem! Late applications of fertilizer, namely nitrogen, should be avoided as it interferes with a plant's ability to shut down for the winter and, therefore, increases the potential for winter injury.

Late spring frosts can also be devastating, especially for early flowering shrubs and even fruit trees. Leaf buds tend to be much hardier than flower buds. Therefore, after a late spring frost, the leaves may open up as usual but there will be no flowers. Leaves that had already begun to expand prior to the frost may become blackened, a common symptom of frost injury. Sometimes gardeners can be a little overzealous when it comes to transplanting annuals into the garden, especially after a long winter. Annual plants are extremely delicate and cannot tolerate frost as well as most perennial species. Depending on the severity of the frost, some annuals will recover (and flowering will be delayed) but some will not. Pansies are perhaps the hardiest of the annual flowers and can be planted fairly early. As for the others, it is best to wait until the last frost has passed. Hardy bulbs such as tulips and daffodils are generally frost tolerant but may be affected if the frost is severe enough.

6. Deadheading

The goal of any flowering plant is to perpetuate itself by setting seed. Seeds come from flowers and once seed is set, flower production is terminated. The term "going to seed" is especially applicable to annual plants. Annual flowers are grown for their extremely showy flowers and their continuous bloom. Although the flowers of some species fall cleanly and naturally from the plant, some require constant deadheading. Deadheading is essentially the manual removal of spent flowers in an effort to prevent seed production and maximize bloom time. If spent flowers are removed prior to seed set, the plant directs its energy into producing more flowers, energy that would otherwise be spent on seed production. Geraniums are extremely common landscape plants that, if not deadheaded, will go to seed and stop producing flowers. If the spent flowers are removed regularly, they will continue blooming until frost. Impatiens, on the other hand, does not require deadheading and will continue to bloom throughout the summer. Some perennials will also benefit from the removal of spent flowers. Deadheading is an especially useful technique for perennials that have a short blooming time. Some perennials, including shasta daisy and dianthus, will continue blooming if the spent flowers are removed promptly. For other perennials, such as delphinium and balloonflower, deadheading can even induce a repeat bloom later in the season. Although deadheading can be used to maximize bloom time and induce repeat flowering, it can also be considered a good way to keep the garden clean and tidy. Deadheading will only enhance flowering in some plants. Proper techniques for removing faded blossoms vary according to plant species. In some cases, only the flower head needs to be removed but for others, removal of the flowering stalk may be necessary.

7. Temperature

Both air and soil temperature can have an effect on flowering. For example, annual plants that are transplanted into cool spring soils tend to take longer to become established and, as a result, may exhibit a delay in flowering. Cool air temperature early in the growing season also tends to delay flowering in many types of plants. However, certain plants may respond favorably to cooler temperatures. Pansies, for example, prefer cool and wet spring conditions and will perform best when exposed to lower temperatures. As the season progresses and the temperature rises, they tend to show symptoms of decline. By mid-summer, they often exhibit a spindly growth habit with fewer and less vibrant flowers. When this happens, it may be worth replacing them with more heat-tolerant annuals. Portulaca, for example, is an annual that thrives in hot and dry summer conditions. Excessive heat may also inhibit flowering in certain types of peonies.

Temperature can also have a great impact on the performance of hardy bulbs such as tulips and daffodils. These bulbs require a chilling period in order to bloom properly in the spring, a phenomenon known as vernalization. If the minimum exposure to cold is not provided, such as in areas with mild winters, the bulbs often exhibit a poor floral display in the spring. This is also important to consider when choosing a planting site in the garden, for even heat from a house/basement during winter can interfere with spring flowering.

8. Planting Depth

Planting depth can have a significant effect on both the flowering process and the overall health of a plant. Most plants have their own depth specifications and failure to meet these specifications may result in bloom failure. For example, when planting peonies, the buds (eyes) must never be more than 4-5 cm below the soil surface. Exceeding this recommended depth is one of the most common reasons why peonies fail to flower. When planting irises, ensure that the rhizomes are no more than 5-8 cm below the soil surface, otherwise bloom failure may occur. On the other hand, spring flowering bulbs that are planted too shallow may also fail to reach their full bloom potential. If the bulbs are not planted deep enough, exposure to high temperatures can damage the flower buds. For example, daffodils that are planted too shallow will often respond with a sparse display of flowers. As a general rule, the planting depth for bulbs should be approximately three times the width of the bulb. It is always better to follow individual plant specifications in order to achieve the best floral display possible.

9. Root Environment

For many plants, the quality and quantity of flowers heavily depends on the amount of soil area that is available to the root system. Many perennials and bulbs require a lot of space and will not tolerate overcrowding. Peonies, for example, should be given a separate growing area, away from all other root systems, in order to optimize their performance in the garden. Perennials and bulbs that begin to show symptoms of decreased vigor and poor flowering may be experiencing the effects of overcrowding. In this situation, digging and dividing the plants will help restore them to their full potential. On the other hand, many plants prefer a smaller, more confined soil area. This is perhaps more common in flowering houseplants, where the root systems are contained. African violet, bird-of-paradise, hibiscus and many common orchids prefer to be slightly potbound and will flower more readily if the roots are restricted. Transplanting these houseplants into unnecessarily large containers will often inhibit flowering. It is recommended, for example, that bird-of-paradise not be repotted after it reaches about 4-5 years of age. At this age, the plant reaches maturity and will begin to set flowers. Because the plant performs best when it is slightly potbound, repotting at this critical time can have a detrimental effect on flowering. It is important to realize, however, that these houseplants respond well to being only slightly potbound and must be repotted before they become excessively potbound.

10. Alternate Flowering

Alternate flowering is a natural, biological phenomenon exhibited by some flowering shrubs and fruit trees. Plants that exhibit an alternate flowering pattern will have alternating "on" and "off" years. They will flower heavily during "on" years but then flower poorly (if at all) during the following "off" year. Some plant species may actually have two consecutive "off" years before flowering again. Alternate flowering is especially common in apple and crabapple trees. Basically, a heavy fruit crop in one year will consume a significant proportion of the plant's food reserves at the expense of the next year's flowers and fruit. It has been suggested that hand thinning excess fruits in an "on" year will help to conserve the plant's resources and reduce the occurrence of subsequent "off" years. Otherwise, the best thing to do is avoid varieties that are particularly prone to alternate flowering patterns. Flowering dogwood is a common shrub that exhibits alternate flowering. Lilac and mockorange may also demonstrate a similar pattern if seed heads are not promptly removed after flowering.

11. Overall Health

Poor flowering can also be pest related. It is important to become familiar with the pests and symptoms commonly associated with the respective plant in order to identify a problem and implement an appropriate control measure. Plants that have been attacked by disease or insect pests usually exhibit visually identifiable symptoms that aid in diagnosis. Keeping plants as healthy and vigorous as possible will help to increase their immunity to pest invasion. This means administering a regimented watering plan and a balanced fertilizer program. Also ensure that stress and injury are minimized throughout the growing season. Apply pesticides only if a disease or insect has been confirmed and always follow the manufacturer's label carefully.

Photos:
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