One of these may be the cause of your plants non-flowering phase. It could help you determine the solution to the problem.
1. Stress
Plants react to stress by shifting from vigorous growth to simply trying to survive. If the plants are growing in poor soil, are overcrowded, lacking water and nutrients, or the weather is hot and dry, they may be reacting to stress. Leaves that have turned a grayish-olive color are a good indicator that the plants are stressed. If this is the case, the plants may begin to die. When threatened with these conditions, plants will attempt to flower and attract pollinators so they can produce seeds to try to survive.
If you think your plants are experiencing stress, try to relieve it. Repot, add fertilizer or water more as needed to help them bounce back.
2. Fertilizing
If your plants look ill, their leaves turning yellow with only a few flowers, they are lacking nutrients. To prevent lack of nutrients, you should apply fertilizer to your potted plants every third time you water or about once a month if your plants are in a garden. Slow release fertilizers work the best because they provide a constant supply of nutrients to the plants and are environmentally friendly.
Tomato plants and impatiens are examples of having thick green leaves but no fruit or flowers and are in a correct state to be able to grow and reproduce. Therefore, they will not produce flowers to attract pollinators. If your plants are overly lush it is most likely that they have been over fertilized and have been put into a vegetative state.
3. Watering
In order for plants to survive they need just the right amount of water. Too much water causes rapid growth of fleshy, weak branches and poor roots. Not enough water causes restricted growth, instigation of the flowering cycle and grayish-green foliage with brittle stems. Water your plants in the early morning at their roots; avoid splashing water on their leaves to prevent diseases.
4. Pot size
Give your potted plants a lot of room to grow new roots. New roots result in more flowers and better plant growth. If your plants are overly crowded, they will stop growing, set seed and die off. When planting in pots in the spring you should plan for a long growing season and provide your plants with enough room to grow. This will be better for your plants and better for you because they won't require as much maintenance.
5. Sunlight
Sunlight provides your plants with the energy they need to produce large, beautiful flowers. Plants that require full sun need at least six hours of sun each day and plants that require partial shade should only receive about four hours of non mid-day sun. Most flowering plants need about six hours of sun each day.
Gardeners can often underestimate how much sun an area receives. Hanging plant baskets usually look better on one side because that side receives more sunlight. You can prevent this by rotating your hanging baskets about once a week.
If your plants do not receive enough sunlight they will begin to look weak, while too much sunlight can turn their leaves an unhealthy silver or copper color. If your plants are receiving the correct amount of sun and they still look weak, they may need more fertilizer.
6. Temperature
Many plants struggle in the summer when the humidity rises and nighttime temperatures are high. These types of conditions cause plants to grow more slowly and stop flowering because they are not able to rest and recuperate from the warm day. It is similar to sleeping without air conditioning and waking up more tired than when you went to sleep. When the nighttime temperatures are high, you should water your plants in the early morning to make sure they have enough water to avoid feeling the stress from the previous day.
7. Dead-heading
If your plants have more dead flowers than new flowers, they need dead-heading. Dead-heading is the process of removing the dead flowers from your plants to help them bloom again so they can produce more flowers.
If environmental conditions have not changed from when your plants were flowering to when they stopped and they are still not producing flowers you should check your plants for insects and diseases.
Source:
www.menards.com
Last year flowers were already flowering by the end of December... in the nord-holland! This is just my experience though, but it's a fact our climate is changing little by little.