Background

Although bedding plants are popular as an ornamental in many gardens, many have been bred purely for appearance and are of little value to pollinators. Some of these cultivated varieties produce little nectar or have become distorted in shape, so that bees cannot easily access them. However, as gardeners are becoming more aware of the value of pollinators, there has been increasing interest in growing bedding plants that will better support them.

Many bedding plants have very limited value to pollinators

The aim of this trial was to investigate the value of Dahlia Mignon series to pollinators and whether flower colour is an important factor determining their attractiveness. Dahlia Mignon are compact plants that produce large numbers of nectar-rich single flowers, so may be a good candidate for a bedding plant that is ‘perfect for pollinators’.

We asked members to grow 3 types of Dahlia Mignon: red, white or purple. On a regular basis, they recorded the number of bees visiting each cultivar for a five minute period. We also asked questions about how they found the dahlias to grow.

Participation in the trial

This survey was done as part of the Blooms for Bees project in conjunction with the Centre for Agroecology, Water and Resilience (CAWR) at Coventry University. The results submitted in paper form through Garden Organic are presented here. To see the rest of the findings from CAWR, visit the Blooms for Bees website.

106 people signed up through Garden Organic to take part in the experiment. Of these, only 23 returned the paper forms, but the majority of people were encouraged to submit the results to CAWR through a smartphone app. The results submitted electronically were added to CAWRs pool of results, where 192 people submitted surveys. The Garden Organic survey gave people without a smartphone, the opportunity to contribute.

Growing the Dahlias

Most of the participants (87%) had grown dahlias before. The majority (45%) had grown them from tubers, although 32% had grown them from seed before, so growing from seed wasn’t new to everybody.

On average, it took 17 days for the seeds to emerge, although as always, with people growing in a wide range of conditions, there was a large range from 5 to 33 days. There was no difference between the varieties.

It took on average 87 days or about 3 months from emergence until they flowered. There were small differences between varieties but they were not significant.

The majority (77%) of people found Dahlia mignon easy or very easy to grow from seed, with only a few people struggling to grow them.

Pests and Diseases

Dahlias do have a reputation for being prone to slug attack, and this was borne out in the results, with 62% of these people suffering from slug or snail problems. One person commented that: “their plants were destroyed within 2 days when they didn’t normally have a slug problem on their sandy soil.”

Slugs were a major problem for many people

Value as a bedding plant

People were asked what they looked for when choosing bedding plants. Flowering period was the most important determining factor with 79% of people rating this as highly important. They also gave high priority to value to pollinators, abundance of flowers and resistance to pests and diseases.

The dahlias were popular as a bedding plant amongst participants with 73% agreeing that they were suitable as a bedding plant and 90% of people liking them for their height, colour and appearance of flowers. Some people commented that they didn’t flower that well compared to other bedding plants, and that it was necessary to dead head them regularly if you wanted a continuous supply of flowers. As a consequence, only 45% said they would grow them again and only 42% would recommend them to others. Just under half (43%) of people planned to overwinter their dahlias so they could grow them next year.

Other bedding plants that were popular choices included Geranium (64% of participants) Lobelia (55%) Snapdragon (45%) and Fuschia (42%). Of these geraniums, snapdragon and fuschia all have value to bees. Pelargoniums which some people may have been included as geranium are of less value.

Value to bees

Bees were observed visiting the flowers from July to October with August being the most active month. It is interesting that bees were still visiting the flowers in October, after many plants had finished flowering providing a valuable food source for bees about to enter hibernation.

People were asked whether the bees visited the Dahlias frequently compared to other bedding plants. The answer to this was divided. 40% said moderately, 40% said frequently, and 20% infrequently or not at all. Many said that when other plants were present, the bees would visit these in preference to the dahlias. Plants that were noted as being very popular with bees were borage, lavender, verbena and phacelia.

Many people found that bees preferred other surrounding plants to the dahlias

Colour preferences

Participants were not clear as to whether bees found either colour more attractive. There was a fairly even split: 32% thought they visited one colour more than others, 37% didn’t see any difference and 32% were not sure. Of those that thought there was a difference, 78% thought that white flowers were more frequently visited and 50% thought that purple was least visited. People’s thoughts were borne out by the actual numbers. On average, in each 5 minute recording period there were 4.8 visits to white flowers, 3.8 to red flowers and 3.2 to purple flowers. However as there was a degree of variability, these differences were not statistically significant (there was a 27% probability that these results could have happened by chance).

“Differences in preference for colours were not that clear cut”

Raising Awareness

As an awareness raising exercise, this trial was a success with 71% of people agreeing that the trial had raised their awareness of how plants vary in value to bumblebees and 67% intending to increase the amount of bee friendly plants that they grew.

There are a number of key things you can do to improve the value of your garden to pollinators:

Choose species of plants that are friendly to bees. Popular plants include lavender, comfrey, borage, phacelia, agastache and marjoram
Grow a range of plants to suit different species of bees and provide a range of flowering periods throughout the season
Grow plants from seeds where possible, as many plants sold commercially have been treated with insecticides
Avoid spraying your own plants with insecticides especially during the day when bees are active
If growing bedding plants, choose single rather than double flowers, which bees tend to ignore.

For more information about choice of plants and species of bees visit the Goulson Lab.