This has been a magnificent season for spring flowers — blooming forsythia, azalea, pink dogwood, wisteria and Chinese viburnum. But my wife, who suffers from allergies, wonders why plants around here bloom with such gusto.

Other folks wish their shrubs would flower at least once during their lifetime. They ask the age-old question: “Why don’t my shrubs bloom?”

If someone asks me that, I usually respond with a few questions: Has your shrub ever flowered? How long has it been in the landscape? Is this the first year it hasn’t bloomed? Has the flowering declined over the years?

Answers to those questions are clues that enable us to determine “what-dunit.” If a plant has never bloomed, the cause could be the climate, soil, light or maturity of the plant. Let’s take a brief look at these factors.

More information can be found in the Clemson Extension factsheet “Why Plants Fail to Flower or Fruit” (HGIC 2361) at http://hgic.clemson.edu.

1. Plant maturity. Shrubs and trees need to go through stages before they are mature enough to bloom. Some trees do not flower until they reach a certain age. Seedling dogwoods generally do not flower until they are seven years old. Seed-grown Southern magnolias may take 10 or 12 years to bloom.

2. Climate. Cold temperatures often kill flower buds while posing no harm to leaves and stems. Winter/spring temperature fluctuations play havoc with plants. Plants that break dormancy and start growing in response to warm temperatures are more susceptible to injury when a cold-air mass suddenly rolls in. It’s not uncommon to find some plants blooming more reliably farther north, where winter remains consistently cold, as opposed to plants in our area that start growing early and lose their flowers to an uninvited blast of cold air.

3. Soil. If plants experience stress from conditions that are too wet or too dry, flowering will be affected. Sometimes an absence of flowers results from inadequate soil preparation. Perhaps the soil pH was too low (acidic) or a nutrient such as phosphorus was lacking. Crape myrtles will survive in highly acid, infertile soils, but they will bloom magnificently at an earlier age when they’ve been adequately limed. Rhododendrons, azaleas and mountain laurels thrive in acid soils as long as their nutrient needs are met. When inadequate levels of phosphorus are present in the soil, these plants will not flower well, if at all. Sometimes overfertilizing with nitrogen will keep newly planted shrubs and trees making lots of leaves, instead of flowers. To determine your soil’s pH and to know what kind and how much fertilizer is necessary, have a soil test taken through your local Clemson Extension office.

4. Light. Inadequate light is the most common reason for a plant not flowering. If a plant has never flowered, it probably was planted in dense shade. If a plant used to flower and then stopped, perhaps surrounding plants or new structures have reduced its sunlight.

Bob Polomski is an Extension Horticulturist at Clemson University and author of “Month-by-Month Gardening in the Carolinas.” He is co-host of “Your Day,” which airs at noon Tuesdays on public radio stations statewide.