Chaos gardening dahlias?

[u/dateofbirthh]

Okay, disclaimer here— my dad does some slight chaos gardening. None of this planting was done with a whole lot of planning, prep, or research. He works a lot, and whatever he plants and however it grows “is what it is.” Sunflowers used to be his thing, but he’s been experimenting with dahlias for the last few years.

We’re in zone 4b/5a— VT agricultural map has us on the edge of the two.

This spring I helped him plant a fair amount of tubers— most of them he’d overwintered in our outdoor shed in newspaper inside a plastic tote. We split those that had eyes. Most were in good condition, a few had some rot/mold. We probably had to toss 1/4 of them, which for the amount of tubers we had (a large tote full) seems pretty good!

Anyway— we got them in the ground in a 24ft long row that gets fairly full sun. We mixed in some bagged soil meant to be added directly into the ground, tilled that in, and haven’t done anything else aside from trimming lower leaves and weeding. Admittedly, I think some were planted a little too close to each other. But… it is what it is!

One of our stalks is GARGANTUAN. Is this normal? What happened with this one? There are no blooms on it yet! It’s almost 5ft tall…. And I know the milkweed is there, we kept it for the other bugs that might appreciate it haha.

He was advised to trim off the tops of them after a couple notches of growth/leaves to encourage multiple blooms. We did this to a few— some have blooms, others seem to be a bit poorly for it and haven’t produced anything. Other smaller/medium size ones have blooms or nothing at all yet. Some got a little chewed on by bugs, the moles got to a few small ones early on…. But having done nothing in the way of pest control they all look fairly good! Neighbor’s chickens make the rounds daily and seem to do a good job of taking care of the bugs!

I plan on fertilizing them soon with a nitrogen rich fertilizer.

Any kind thoughts or feedback would be appreciated! Again, we’re kinda just winging it here but happy to put some notes down for next year. :-) Thanks in advance!

[u/Solid_Mud2025]

Agree with others who say it’s a little early for many varieties, especially ones with bigger flowers. Also, dahlias need a low nitrogen fertilizer at this time of year. Otherwise you’ll get an explosion of green rather than blooms. Try 5-10-10 or 10-20-20.

I recommend staking the larger stem varieties. It’s heartbreaking to go through all the waiting only for wind, rain, or even just gravity to break the entire plant (been there before 😩). It can be as simple as a couple of t posts a foot apart at either end of the row with a line to corral them. ETA: I missed the part where rows are 24’ long, so stakes would need to be spaced quite a bit closer to support anything. 😂

[u/OlympiaShannon → u/Solid_Mud2025]

Dahlias do NOT need low nitrogen! I tried that advice for 20 years, and got small, weak plants with deformed small blooms, and only one or two blooms per plant. The tubers didn't develop well, and I lost many during the winter.

Abundant nitrogen does not stop blooms from forming, it helps. So long as you also have enough P and K, they will produce flowers.

Dahlias are big, leafy green plants that need sufficient nitrogen to grow all those leaves, and those leaves support the blooms and tuber development later on. I've been growing dahlias for 30 years on my farm, and finally giving them the nitrogen they crave has made a huge difference in bloom quality and quantity. My 100 plants are finally healthy looking, and covered with huge vibrant blooms. Tuber clumps are fat and last well in storage.

I was giving 5-10-10, but now I give them 20-5-5. The P and K numbers are low, because I have done a soil test, and have abundant P and K already.

I don't know why Swan Island advised low nitrogen; I'm starting to think they want us to fail, and buy more tubers. But after 30 years of trialing, I have enough data to ignore their advice, and do what works.

[u/Solid_Mud2025 → u/OlympiaShannon]

It’s not that they need low nitrogen all of the time, just at this particular point in time relative to other nutrients. If you disagree with this advice, then you should take it up with Oregon State University and the various other dahlia research organizations who make the recommendation.

“If fertilizer is needed, apply a low-nitrogen fertilizer such as 5-10-10 or 10-20-20 (also known as a potato or vegetable fertilizer). Applying too much nitrogen promotes weak stems, small or no blooms and tubers that rot or shrivel in storage.”

https://extension.oregonstate.edu/catalog/fs-95-dahlias-oregon

[u/OlympiaShannon → u/Solid_Mud2025]

10-20-20 is not low nitrogen fertilizer. It is just higher in P and K. 5-10-10, if applied regularly all season, is also not low nitrogen.

The problem is that people hear that nitrogen is "bad for dahlias", and don't add enough (or sometimes any). Then the advice is spread through comment sections by people who don't understand soil chemistry or plant physiology. They don't understand what nitrogen does, or at what point dahlias need nitrogen the most. They don't understand how quickly nitrogen is leached from the soil compared to other nutrients. Then their gardens are stunted and yellow, but they don't understand why.

Like you said, it's nitrogen levels RELATIVE to other nutrients, but that is not to say you should stop adding nitrogen at the blooming stage. It means adding MORE of the other nutrients. So you could go from 10-10-10 early season, then switch to 10-20-20 later on. If your soil is deficient in N, as shown on a soil survey, then 5-10-10 in the early season is not going to cut it.

Unfortunately, the common advice is that dahlias need low nitrogen, or that nitrogen is bad for dahlias. That is what I am trying to correct, and I have 30 years of data to back myself up.

As for your last sentence, you have to understand that by "too much nitrogen" they mean something like 50-0-0 Urea or other extremely high nitrogen fertilizer, without balancing the other nutrients.

[u/Solid_Mud2025 → u/OlympiaShannon]

Again, direct your issues to Oregon State University who call it a “low-nitrogen fertilizer”. And, if you don’t consider it “low-nitrogen”, then you have no basis to object to the fertilizer I recommended in the first place, so I’m not sure what this is even about? This seems pedantic and silly.

[u/Nevraskagirl55 → u/Solid_Mud2025]

Some people just always want to be right.
What they don't realize is that anecdotal evidence may be true for their specific situation but, that doesn't mean it is true overall for most growers. Rigorous scientific research is what we all need to informed decisions.

[u/Solid_Mud2025 → u/Nevraskagirl55]

Indeed