I am so discouraged. 3 years of trying to grow my dahlias and they come up and stay short. I have done everything I can think of for the soil and have them in raised beds. I guess I will have to move!
While moving might be one option, there are a few other things to explore before changing states. :)
How's your soil? Rocky? Dense? Well-draining or slow draining? Do you have a lot of organic matter in the soil where you grow your dahlia?
Dahlia like well-drained soils with decent levels of organic matter, and a pH slightly on the acidic side (but they're really tolerant about pH in many cases). If your soil is poor, you can dig in some well-cured compost this fall and, by spring, grow nicer dahlia.
Do you feed? Contrary to popular belief, dahlia are actually pretty close to average feeders (but they are on the low side of average). I feed my entire garden monthly with 18 pounds per thousand square feet of Milorganite. That's still not sufficient and I enhance with Miracle Gro.
How warm does it get? Dahlia do like warm soil, so places that regularly drop cold at night and don't get terribly warm during the day aren't great for them.
Plant them in south face gardens to maximize their warmth.
How much sun do they get? Dahlia demand an absolute dead minimum of 4 hours per day--but they'll be short and won't bloom much. At 4-6 hours they tend to be very, very tall as they reach for sun and bloom just fine. Over 6 hours they're usually close to their stated height and bloom spectacularly.
How long is your growing season there? Not that it matters much, my Blue Boy and Sun Lady bloomed before day 60. However, longer-developing dahlia (like my Color Spectacle) do take more time. Generally--but hardly a rule--dahlia with smaller flowers will develop faster but there are so many exceptions it's ridiculous.
it's not your state. Check in with the Colorado Dahlia Society.
Where are you getting your tubers? Are you planting tall cultivars? Many garden centers sell bedding dahlias that are not intended to get very big.
Here is a link that might be useful: Colorado Dahlia Society
I have seen your posts on the web for couple of years now. Many people have tried to advise you. Sounds to me like you ought to try growing them in a neglected area of your garden that has had no soil amendments or exotic fertilizers. For the remainder of this year, I would blast them with some Miracle Gro and that should overcome all the soil deficiencies. If the plants cannot take up nutrients from your soil, maybe they can through their leaves. Many people successfully grow dahlias in Colorado.
Yes many people have advised me. I thought that is what the Forums were for. I use raised beds, bonemeal, and garden soil with Yum Yum mix and that is it. I buy my tubers from Swan and they all showed in June. Nothing grew in July and than they started again in August. They seem to grow wide and not tall even when I pinch on the 5th leaf. I have been growing dahlias for yeas in NE. but have moved to CO. 3 years ago. I sent my soil in for testing so I think I have covered everything. I use a foliar spray in August. Mist when it is hot.
Hi, I sucessfully grow dahlias in northern Utah. I am not sure where in Colorado you are but I think our climates may be similar. I also struggled for a few years...I planted them in too much shade, didn't water them enough etc.
Finally, I made a raised bed in almost full sun all day long. Once they are up and growing, I water them A LOT. I never let the ground dry out around them. They get watered by the sprinkling system but I also hand water them with the hose every night. They grow really well now. I don't fertilize them much, maybe a little bone meal at planting time and some miracle grow once during the summer. I truly believe the key in my sucess is lots of sun and lots and lots of water. It is very hot here in the summer and they need a lot of water.
>>I use raised beds, bonemeal, and garden soil with Yum Yum mix and that is it. I buy my tubers from Swan and they all showed in June. Nothing grew in July and than they started again in August.
Underfeeding? I keep seeing recommendations that sum up to "don't feed your dahlia."
The Yum Yum helps, but it's only 2-1-1.
At least in my garden and all the ones I'm familiar with around here, that's wrong. Dahlia are definitely below average in the feeding requirement department, but they do require nitrogen to develop appropriately (as does any plant).
I might recommend trying an application of Milorganite when the greenery shows above ground. It's a good, slow fertilizer that will last for at least a month (and takes some weeks to get working as it requires time to decay into the soil). Any other good organic fertilizer would also work fine.
I apply 18 pounds of Milorganite per month in the garden from May 1st to August 1st. They also get somewhat under half rate Miracle Gro weekly,
Over the past few years, I've also adjusted my phosphorus levels to around 1,000 pounds per acre (on the Logan test, your mileage will vary on others due to different testing methods). That got rid of the late July lull in the gardens and increased blooming overall to levels that are...well, stupendously high.
Poor growth and blooming can arise from a lot of different shortages, but nitrogen, phosphorus, potassium, calcium, and magnesium are the heaviest hitters. Boron can be another problem, but tends to be more subtle.
I do the soil test reads over on the lawn care forum, but I'll sure be happy to take a look at yours over here if you like. Just post the results (and black out your name and any identifying information).
Watering, as Linda mentioned, is another major point. I do find that dahlia (and most other plants, for that matter) prefer to be somewhat damp at all times, with minimal periods of soaking wet and bone dry. Your raised beds help with avoiding wet feet, but do require a little attention to avoid going dry.
Sun, water and fertilizer are the three ingredients for successful gardens. I like the post from the person in Utah. Another comment is that Swan Island Dahlia varieties do in general grow a bit shorter than others. They breed them that way as they do not stake their dahlias on their 45 acres of flowers.
I have grown many tubers from Swan Island and they have grown well for me. Most of my plants are between 5-6 feet tall with the exception of ones that are supposed to be shorter varieties.
Every year I give tubers away to friends at work. Most of them have no luck growing them and I know it is because they assume the sprinklers water them enough. I tell them every year that they need to water more...
It is hot and dry here in the summer and we don't much rain although this August has been an exception. Cooler temps and more rain. I love it!
Here is picture of some of my dahlias.
Thanks to you all for your advice. I will try the Milorganite next Spring. I have such nice green leaves that I shy away from anymore N. I have had the soil tested and have no idea how to get it too you. PH is7.4. Too much salt, to little N. I have tried to adjust to both. How big is your garden that you use 18 lbs of the Milorganite?
At the present instant, I have a Sky Angel dahlia that's trying to take over the mailbox garden. I'm going to allow it to do so and already moved the gladioli that were there. It blooms like a trooper and sees what most would consider way too much nitrogen.
If you can turn the test results into an image, great. If not, you can type out the numbers. I usually screen shot my PDF and save it in (free) Paint Shop Pro...or at least it was free when I got it. If not, there are tons of others that are free. Then just use the Image file to upload button right under the post a follow up link and it'll upload to your message.
My gardens are right around 2,000 square feet (although that tends to grow a little every year)...so I'm using a full bag monthly from May to August, or 18 pounds per thousand square feet, or just about 0.9 pounds of nitrogen per month.
This is in addition to the 0.2 pounds of nitrogen from synthetics per week, for a total of 1.7 pounds N per thousand square feet per month, May to August. September is much lower at about 0.5 pounds N per thousand square feet. October is 0, except what spews over from organically feeding the lawn.
While many gardeners would call that excessive, I do demand a lot of the gardens. There are 750 annuals planted yearly, and many perennials and bushes in there. It's pretty packed and I won't tolerate anything but wall to wall blooms from July 15th through October 10th.
Too much salt can be a major challenge when growing plants--sodium is toxic in high amounts. It's also typical for Colorado soils (and soils everywhere that see lower rainfall amounts). Normally we'd recommend calcitic lime to dispel the sodium, but in your case with your pH already high, that's not a good option. While I need to see the report, gypsum might be a good option as it dispels the sodium without altering the pH.
7.4 pH is very alkaline. Dahlias like the soil to be between 6.1 and 6.7 pH. I believe the remedy that they prescribe is sulfur. As I said before, Miracle Gro and especially the acid Miracle Gro would help. You need to lower your soil pH.
In Colorado, there's almost certainly a fair clip of sodium and calcium bound to the soil.
Surface applied sulfur is pretty much useless. Dig the recommended amount into the soil in the fall--the stuff takes a long time to work. Right when you remove your dahlia for storage is a great time to do this.
Even then, don't expect too much in many circumstances. It can dispel the sodium and calcium in the soil solution, but there's plenty bound up (and probably limestone bits) that will happily release calcium when the sulfur is gone.
Organic material makes any given pH matter less as it holds a lot of soil resources, and gives them up to plants fairly easily. Highly organic soils tend to drift toward neutral (the excess resource points get tied up by hydrogen) and widen the tolerance range of many plants.
That's why I grow great azalea and rhododendron with no sign of chlorosis at a pH of 6.6.
If she had 6.6 pH she would not be writing about not being able to grow dahlias. Many fertilizers are acidic and would help but it is very late in the year to be using any nitrogen on dahlias unless your are not concerned about keeping the tubers. I have noticed that by using liquid fertilizers of the proper pH for our hanging pots, that the plants thrive. I had used neutral liquid fertilizer and they did poorly. Some require very acidic conditions and although the potting soil is not very acidic, the addition of the acid based liquid fertilizer really works. I bet that acid based fertilizer like the acid Miracle Gro that I use on the hanging pot plants that require acid would work on the dahlias.
>>If she had 6.6 pH she would not be writing about not being able to grow dahlias.
Hence the reference to azalea and rhododendron, which don't flourish at that pH. They turn yellow and usually die. Pennsylvania soils, where I am, tend to be extremely acidic--we have the opposite problem.
>>I bet that acid based fertilizer like the acid Miracle Gro that I use on the hanging pot plants that require acid would work on the dahlias.
For a time, sure. More permanent pH shifts can be anything from trivially easy (sandy soil with low organic matter) to a major battle (muck soils).
Digging in the sulfur gives it all winter to work, and for the resulting salt (gypsum, calcium sulfate), to wash out. Not that there will be a great deal of washing out in most of Colorado, but at least calcium sulfate isn't a particularly desiccating salt.
Another idea might be to try Holly Tone (an Espoma product). That can be mixed in at planting time next spring, and at 4-3-4 it's a nice, balanced feeding without excessive nitrogen (and the nitrogen is all very slow release anyway).
Since dahlia tend to surface root, application up top for the remainder of the year every month or so of the Holly Tone should help.
And on the non organic list would be ammonium sulfate that acidifies soil as it fertilizes. It is dreadfully bad here where our soils are already too acidic. Soils tend to return to their "native" pH after a year or two, so you need to always monitor your pH levels. Our lime applications wear off in about two years. Our soil wants to be 6.1 pH and if we add some acid forming fertilizers it creeps lower. I add about the same amount of lime as I do fertilizer to maintain about 6.1 to 6.2 pH. I would imagine where you are trying to reduce pH you need to add sulfur quite often and monitor it. PH meters are only about $10.00 nowadays.
If life gives you lemons, make lemonade!
You could try plants native to Colorado, there's some very lovely natives. I'm sure they'll do better there than Dahlias would.
This post was edited by dbarron on Wed, Aug 27, 14 at 14:35
>>If life gives you lemons, make lemonade!
Unless life also hands you a fair bit of sugar, your lemonade is going to be terrible. :-)
>>PH meters are only about $10.00 nowadays.
And dreadfully inaccurate even under optimal usage. Fortunately, we have an initial test here, so you can use a relative change on the pH meter. it won't be very accurate, but I'd trust it over about 0.5 points or so.
>>Our lime applications wear off in about two years. Our soil wants to be 6.1 pH and if we add some acid forming fertilizers it creeps lower.
Ditto, except my soil wants to head for 5.2.
It's never easy, is it? Well, fortunately a good calcitic lime is fairly cheap, effective, and very fast--and I tend to leach calcium far more than magnesium anyway. Blame the acid rain.
I have a $125.00 pH meter and the $10.00 meter. They read within .1 of each other. And as you say, you are trying to chart your progress and the cheap one would give you a starting point and tell you if you are lowering the pH.
Are you sure either is accurate? All the pH meters I've had have read in the same range--all of them wrong by almost 1 point.
I did try a simple soil-water-reactant test out of idle curiosity. The pH actually was very accurate...if I were trying to test the pH of our water.
good Lord! I did start a hard topic. This year in CO, it has rained constantly. Never happened before. That will help wash out the salt in my soil as it was high in salt. I have basically solved the whole matter. Moving back to where I came from and had big, tall, thick dahlias. I do love some of the CO plants and hope to try some. Thanks for all your info.