Dahlias - 10 things you didn't know

I have recently been reading a book on Dahlias by Gareth Rowlands, and thought you might be interested in some of his points.

1) Garden and exhibition Dahlias are all given the name Dahlia x variabilis. This is not the name of a species, but just a posh way of saying that they are all complex hybrids and that no one can be sure of their parentage. There are 27 species (ie types that occur in the wild) but they are all weedy and not seen in gardens.

2) Dahlias come from Mexico and Central America, where the tubers were eaten in the past.

3) Dahlia tubers should be started into growth in spring by putting them in a box or a pot and half covering with compost with a little moisture. and given heat. There is no evidence that light is needed. So you could start them in the airing cupboard or in a heated propagator or just laid out in a sunny place. When the growth is about 4 inches high you can plant them out, typically 8 inches deep. But remember the foliage will not take any frost.

4) Dahlias have strong leading tip (apical) dominance. This means that the leading tip produces chemicals that inhibit side shoots. So you need to pinch out the tip to get bushy plants. If you pinch out the tips you will get a large number of smaller blooms. If you pinch out the buds on the side
shoots you will get a smaller number of larger blooms.

5) Dahlias are 95% water and need lots of it. They need the equivalent of 18 inches of rain during the main growing season, which is more rainfall that the wettest parts of Britain. So keep watering them even in the rain. :D Even in damp soil, during hot weather the plants could droop as their folige may be losing water faster than their roots can draw it up.

6) Once a bloom is the size of a pea, it is fully formed. That is to say it has the same number of cells as a full bloom. All that is needed to go from a bud to a bloom is the uptake of water. So keep watering.

7) Dahlias actually grow more at night than during the day. Like all plants they use sunlight, water, and carbon dioxide to photosynthesise, making sugars and starches. These are then transfered to where they are needed and burnt to produce the energy for growth. As long as there are enough sugars this burning process will continue at night, using up oxygen and giving off carbon dioxide.

8) Most Dahlias are short day plants. This means that they will only start to flower when the day length shortens. The longest day length in London is 16 1/2 hours on June 21st. But most Dahlias won't flower until the day length is less than 14 hours. This means that many Dahlias won't start to flower till mid August, irrespective of how early you started them off.

9) In autumn, dig plenty of organic material into the ground to improve its water retention. It doesn't matter if it is only partly composted. Don't feed when you plant the tubers in spring. The roots must be encouraged to seek out water. When the Dahlia is growing strongly you can give it a high potash feed, but don't overdo it. Cut back any feed when it is well into the blooming period. Only water turns buds into blooms, so feed will not help - it will just produce more foliage. At the end of the season, a high potash feed will help to make firm healthy tubers again.

1O) Lift the tubers just after the first frost has killed the topgrowth. Store them overwinter at 4C to 7C in a fairly, but not totally, dry place. The actual storage medium doesn't matter. It could be old compost, sand, shredded paper, under old sacks etc.

 

And if I'm not mistaken, Dahlia's have NO scent...please correct me if i'm wrong (none of mine did last year anyway, and I had about 20 different varieties).

 

Yes, I think you are absolutely right Bashy. I just looked through Rowland's book again and there is no mention of scent anywhere.

However I did a Google and it appears that they are trying to breed ones with scent. I came across this - http://www.jrg-dahlias.co.uk/dahlias_with_sent.htm

.

 

Thought I might be Peter. I for one love Dahlia's. Next to roses they my fave plant. Would definitely be interested in a scented dahlia. Very interestimng link. Will keep my eyes peeled for those.
cheers

 

" 10 things you didn't know"

Actually 8 things I didn't know ... 8 very interesting and helpful things, thanks! :thumb:

 

Great post! I also learned a lot and my dahlias are just getting lovely and big now. I did think the early start would make a difference.......live and learn!

 

Thank you PeterS A lot of useful information there.
I didn't know they were short day plants so that explains why I can't get them into flower early no matter when I start them off.

 

"8) Most Dahlias are short day plants. This means that they will only start to flower when the day length shortens. The longest day length in London is 16 1/2 hours on June 21st. But most Dahlias won't flower until the day length is less than 14 hours. This means that many Dahlias won't start to flower till mid August, irrespective of how early you started them off."

Hi PeterS. Interesting, as I have one with a bud that is showing it's colour

Cheers...freddy.

 

Well my first ever Dahlia is doing great - loads of foliage so far. I look forward to the flowers...

 

Following the advice here, I'm watering them constantly.

 

Every time I see a Dahlia I am nudged to get some, but then the thoughts of planting, then lifting and storing in the basement hit home and I just move on.

 

Well I grew 22 last year from bulbs, starting them indoors, then planting out in May. Some of them grew to about 5 foot and were absolutely stunning. I left them all in the ground over winter (didn't even bother mulching-I am a definite fair weather gardener ;-)) and after the very cold winter we had thought I would have lost all of them. I have lost some, but on just counting 13 have survived. Not bad I say. I wouldn't rule them out redstar...they are a lovely flower. Just leave them in the ground and keep your fingers crossed...you may be pleasently surprised.

 

Hi again. There you go

 

What a lovely colour freddy - obviously not a short day one.

Bob, it will be interesting to know how much scent yours has. With a name like "Honka Surprise" I would expect to have a really powerful stench. :D I am not sure that is the most delicate of names. But what does it matter if it performs.