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I have bought Dahlia tubers from a big box hardware store. According to the packages there are 3 plants per package.

Each package contained 1 clump that was about fist sized and two smaller clumps (size of the smaller clumps varied wildly).

I bought 3 packages: Blue Boy, Thomas Eddison and Arabian Night.

I have some pots that are 30 cm wide and 25 cm high (around 12 inches wide and 10 inches high in the imperial system).

I've read that I should plant these indoors 4-6 weeks before the last frost date which is about now.

Considering I want to maximize the number of tubers per pot, how many per pot can I realistically plant.

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  • Do you intend to keep them in the pots all growing season, or will you be transplanting them into the ground when the danger of frost has passed?
    – Niall C.
    Apr 16 '18 at 19:12
  • @NiallC. Preferably I'd like to keep them in pots. But I may transplant them if the specific cultivars aren't suited for containers. I'll have to look into which ones are better suited for containers.
    – Gilles
    Apr 16 '18 at 19:14
  • All three varieties you mention are large dahlia types, not bedders - you should expect a height and spread for each plant of around a metre by 50 cm - which clearly means a pot for each one. Check the almanac.com link below for the recommended planting distance for large varieties.
    – Bamboo
    Apr 16 '18 at 21:17
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According to almanac.com you should plant them 9-12" apart. Your pots are 12" wide so I would only do one per pot, with the intention that your keeping them in the pot through-out the growing season. Doing more than one will cause the plants to choke each other out as the roots grow taking more and more room in the pot.

If you are going to transplant them out of the pot I son't see why your couldn't do two or three of them, just don't leave them like that forever or they will die for lack of room in the long run.

Another thing as well if you keep one in a pot through-out the growing season is making sure they are fertilized every so often. They will eventually run out of nutrients and will need new soil or something added.

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  • Oh I totally agree Ljk2000! One bulb per 12 " pot, potting soil only. The bulb IS the food for the plant to get it mature enough to make its own food. After that, a little fertilizer now and then depending on what formulation you chose.
    – stormy
    Apr 16 '18 at 21:16
  • I've looked at the link and it mentions that 9-12 inches is for smaller bedding dahlias. It mentions 2 feet for smaller flowering dahlias and 3 feet for larger flowering dahlias. I've seen dahlias sold potted in garden centers, but they may have been specifically for types of dahlias that are better in containers.
    – Gilles
    Apr 17 '18 at 12:22
  • @Gilles eeek I saw the 9-12" and as soon as I did I thought it was the answer. Well in that case I think you can plant them now and get them going. You can always buy a larger pot and transplant them. Sorry for not catching that!
    – Ljk2000
    Apr 17 '18 at 13:07
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Giles, do you have freezing temperatures during the winter? The most vulnerable part of any plant are the roots. Plants in pots absolutely need to be kept where their soil will not freeze.

If this is the case, like all Dahlia owners and growers, you will be bringing your pots inside, removing the tubers, storing them in sawdust and or newspaper in the dark and in an unheated garage (stays 40 to 50 degrees Fahrenheit). You will then be able to repot in the spring, in potting soil only.

I would plant no more than 3 bulbs in 12 "...2 smaller dahlia 1 big one? I would definitely find super 'filler' or 'framing' plants to insert. Low plants that cover the soil, vines to drape over the sides. Here is one of my favorites; Orange Sedge, Ipomea in lime and Dahlias. Breathtaking combination. Do you have room for a 32" pot, 18" pot and a 12" maybe 4 or 5 6" pots of orange sedge arranged at the bottom of the 18" pot? Turn a pot upside down to raise a few pots?

I would use Osmocote 14-14-14, half the recommended amount. Simple, sterilized potting soil without added fertilizer or water holding gimmicks.

Find pots that are 'related' by color, form, material. Not the same pot different sizes but that works too. You want the plants to be the focus.

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