Do you trust this advice from Swan Island

veryzerJuly 5, 2010

I purchased several tubers from SI this year and followed their instructions for container planting, namely, to mix two parts garden soil with one part potting mix. I know for many plants garden soil is a no-no because it retains too much moisture. In any case, my fire magic is nearly bare of foliage, neon splendor, while blooming (disappointingly), has lost it's share of leaves, and Thomas Edison, late to come up, is yellowing some. I really don't know what I'm dealing with aggressive fungus, too much rain. Plus, I feel uncertain as to when to water. At this point, though the surface is dry, the pot with a depth of 12" is still damp/moist about 4" down. I've grown one dahlia, Seattle, in a pot using just potting mix. I don't know if I was lucky or it's really easy, but its performance was absolutely terrific (from Walmart).

I'd be happy to post pics, but any initial reaction to this potting recipe? I've posted a question on container recipes before but the one response I got was much to complicated for a simpleton like me....about five or six different components mixed in separate stages with some of the ingredients overlapping....I just couldn't find some of the stuff or follow the directions.

Sorry to ramble.

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Growing full sized dahlias in pots is challenging in most locations. I believe that pots stay too warm in most climates. There are advantages in using all potting soil rather than mixing in some garden soil. The biggest issue is pathogens in your garden soil. Also, what type of soil you have is an issue. I know of a dahlia grower that has sandy clay soil and it makes excellent potting soil without any additions. When I grew some dahlias in 10 gallon pots, I used all potting soil. I also planted a rooted cutting that was about 12 inches tall in the pots. The plants grew very well and had 2 blooms, then 4. After the four blooms they did not do well. The variety was Cornel, the red ball dahlia. I no longer grow dahlias in pots except for my pot tubers that are in 4 inch pots.

    Bookmark   July 5, 2010 at 11:18PM
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I tried growing three plants in large pots this year, and am about to put them in the ground because the flowers have shrunk. It is just too hot. Flowers grown in smaller pots were fine last year but only because of the cold and rain.

    Bookmark   July 6, 2010 at 12:43PM
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jroot(5A Ont. Canada (near Guelph))

See my comments here:

I agree with Teddahlia. If the roots get too hot there is a problem. Hence one can either double pot or use very large styrofoam pots.

    Bookmark   July 6, 2010 at 3:39PM
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Interesting feedback. I never thought of heat. So what about plants marketed as "container dahlias"? Are these more likely to be successful because of heat tolerance or do they get that name solely based on size?

And I'm using Miracle Gro garden soil. I don't know if they cook the soil to remove pathogens or what.

    Bookmark   July 7, 2010 at 12:12AM
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"So what about plants marketed as "container dahlias"? Are these more likely to be successful because of heat tolerance or do they get that name solely based on size? "

Yes, smaller plants have smaller root systems. It may be a function of both heat and water with larger varieties in pots. They require an awful lot of water in a pot. Probably because warmer soil allows more evaporation. A partially buried pot seems to work really well; even smaller pots can be used.

    Bookmark   July 9, 2010 at 3:44PM
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I got a Neon Splendor from SI this year, it is in a clay pot and is spectacular!

I also bought Fire Magic (though they apparently delivered Dark Magic instead), it is in the ground and growing slowly, albeit with 2-3 beautiful blooms so far.

I have found advice from SI to be right on. They admit (as do most growers) that it is harder to grow dahlias in containers than the ground and I have found that to be true as well. One of my PAST mistakes though was underwatering. I had read so much about not watering dahlias after planting and having lost several that rotted anyway, that I held water back sparingly. I re-read their catalog this summer and it actually says you can't overwater dahlias (I'd heard that about roses years ago) once they start sprouting and blooming. So now I soak mine to the bottom every 3-4 days instead of the light 'washing' I used to give them every 2 days and they are loving it!

As for what soil I used in the containers? Lord only knows. Parts potting soil, part planting mix and part sand (I live in the dunes of S.F). The sand keeps them draining easily, the potting mix seems to be light enough for them to push through and the planting mix seems to keep it all together.

But other containers of mine are ALL planting mix or all planting soil (exactly what you are NOT supposed to put in pots) and they all are ablaze in blooms this year! In my opinion, the soil won't matter much once you start feeding them the right stuff (little to no nitrogen) and include blooming fertilizer that strengthens the stems and allows for blooms to do their thing!

    Bookmark   August 7, 2010 at 1:36AM
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