Assessing Effectiveness of Various Methods for Overwintering Dahlias in Zone 6 and Subsequent Effect on Bloom Time

View the project report

Commodities

• Additional Plants: ornamentals

Practices

• Crop Production: no-till, season extension, winter storage
• Education and Training: farmer to farmer, on-farm/ranch research

Digging and planting dahlias
tubers represents a huge labor expense for dahlia growers. 
Though some have successfully overwintered dahlias in warmer
climates, little information is available for our growing
zone.  The vast majority of flower farms in the US employ
just one person.  This makes dahlia digging, washing,
storing, and replanting a huge portion of their available time
and labor.  Alternatively, leaving dahlia tubers in the
ground over winter can be an enormous financial risk as dahlia
tubers are relatively expensive. 

In addition, flowers that bloom
earlier than their traditional season command a higher price due
to their rarity, specifically dahlias which do not ship well and
are highly sought after in the wedding flower sector. 
However, there is very little specific data on how much
difference can be seen in overwintered dahlias, especially
between various methods and planting locations. 

Solution:

By evaluating the success of
various techniques for over-wintering dahlias, I seek to give a
more definitive answer to whether it can be successful and which
methods work best in zone 6. 

Furthermore, in warmer climates,
it is generally accepted that successfully overwintered dahlias
bloom earlier than their spring-planted counterparts. 
Additionally, those overwintered in a high tunnel bloom earlier
than their field grown counterparts.  This study will record
whether that is true for our growing zone and, if so, is that
difference statistically significant.

In this study, I will have 5 test
plots, each with 50 dahlia plants: 

1. control/traditional method:
   dahlias are not overwintered and spring-planted instead
2. high tunnel covered with leaves
   or straw mulch and then topped with reusable weed barrier as a
   tarp
3. high tunnel with no mulch, only
   weed barrier fabric as a tarp 
4. field grown (outside high
   tunnel) with mulch layer and weed barrier as a tarp
5. field grown no mulch, only weed
   barrier fabric as a tarp

I intend to plant two varieties
of 25 dahlias per test plot for a total of 50 dahlias per plot.
Different varieties of dahlias bloom in fewer numbers of weeks,
so this will help determine if bloom time can be optimized within
specific varieties or forms of dahlia (ie: border dahlia vs
dinner plate dahlia).  I will record the success rate of
overwintering for each plot.  I will also record the first
bloom date for each plot.  I will then determine the
significance of any difference between the
plots.  

High tunnel space is valuable,
and this data could help determine if it is worth using high
tunnel space for this crop, or conversely, if the difference is
not significant enough to devote this space to dahlias and would
be better spent on other crops.  

If at least some varieties of
dahlias could bloom in early June, or better yet, May (peak
Spring wedding season in this region) this could make a high
value flower, even more valuable for local cut flower
farmers.  This research will give growers more data to
consider if overwintering their dahlias is beneficial to their
operation.

Objectives: 

1. Evaluate the effectiveness of 4
   methods of overwintering dahlias
2. Record first bloom dates for
   dahlias among the 4 different methods as well as of the control
   group of Spring-planted dahlia tubers.
3. Share findings through
   (minimum) 2 blog posts, 2 social media posts, a published
   article in a cut flower specific publication, and 1 field
   day.