So this is my first year trying to grow dahlias. (Before this season, I’m not sure I had ever even heard of a dahlia, to be honest.) But I jumped in with both feet this year and have 19 different varieties growing from tuber, with another four varieties from seed. But while was recovering form knee surgery this spring I had a lot of time to research all things dahlias.

One of the things I came across was crown gall. One of my favorite YouTubers, Nicole from Flower Hill Farm, had an absolutely horrible season this past year with her dahlias–they were really short (around a foot tall, when they should have been 3′ at least) and produced few blooms. It turned out when she dug them up that a lot of them had crown gall.

What is crown gall? Well, it’s a pretty gross-looking disease that affects not just dahlia tubers, but fruit trees, roses, and poplar trees, as well as many others. Essentially it’s a cancer–it causes a tumor to grow on the roots or trunk of plants and causes the plant cells to replicate endlessly. This is both ugly and can be dangerous to the health of the plant.

Crown gall on an apple tree trunk

If the plant is big and old enough, this is just an annoyance, but if the plant is small or young, it can kill the plant. It’s caused by a bacteria that is highly contagious and can live in the soil for years. Apparently the only cure is a biological control bacteria called “Agrobacterium radiobacter K-84″; which, for whatever reason, isn’t available at your local garden center. So if you find a plant that has it, you’re pretty much stuck.

And the problem with growing things from tubers is that the tubers can often arrive already infected, and you’d never know.

I’ve come across three instances of it in the past few weeks. My first experience with it was a tuber I received maybe two weeks ago, from Breck’s. It was the “Emperor” dahlia, a pretty dark-puple velvety dahlias. When the order arrived, I found two tuber clumps–one of which had normal-looking eyes on it, and one of which didn’t. I wish I had thought to take a picture of it, but I was paranoid and threw it out immediately. (Update: I did take pictures!)

Crown gall on my Emperor dahlia tuber clump

Nicole from FHF says that it looks like cauliflower, and I can see why. See all those light-colored bumps at the top of the tuber clump? These, if there were only, say, one or two of them present, would be considered “eyes” and be a thing of happiness, as it would indicate that the tuber was viable. In this case, however, the presence of five or more “eyes” in pretty much the exact same spot means that the tuber is infected with crown gall and needs to be tossed.

So with the Breck’s dahlia, I could tell from the get-go that the tuber had gall. The second tuber clump, packed in the same bag with dry peat moss as the first tuber, did not show any signs of gall. I’ve since potted it up, and the two viable eyes from that clump are now sprouting–but there are only two eyes sprouting, not ten. I’m assuming that it also has gall, but I’m potting it up in a separate container just in case. If it has gall, the growth of the flower should be slow and stunted, so we’ll see.

The second tuber I found that had gall was “Pacific Time”, one of my Walmart purchases. (Walmart’s dahlias are supplied by Van Zyverden.) This tuber passed muster when I inspected it initially, and when I sprouted it it only had one or two sprouts, as per many of my dahlias. However, when I went to go plant it into the garden bed, I accidentally broke off the sprout while I was getting it out of the temporary pot. Which was weird, because sprouts tend to be pretty hardy, from what I can tell. So when I went to go inspect the damage, I found the sprout that had popped off had five other mini-sprouts connected to it, just under the soil line. The tuber itself also had several more mini-sprouts trying to grow, right from that same spot. Thus, my diagnosis of crown gall. So out went all of the Pacific Time tubers as well. (It’s kind of an ugly dahlia, really; I’m not too beaten up about it.)

The third instance was tonight–again while I was trying to plant dahlias into my garden bed. The culprit this time was “Great Silence”, from Longfield Gardens. (As I ordered most of my dahlias from Longfield, this freaked me out a bit and now I’m tempted to go dig up all of my tubers because clearly this disease could be anywhere.)

Crown gall on my Great Silence tuber

Again, the sprout itself had at least four other sprouts attempting to shoot from that same exact spot on the tuber–and this tuber was just the eye/neck/body, rather than a whole clump of tubers. The only sprout I saw on the potted dahlia was one large one; I had no idea there were four more just under the surface.

I’m so glad I decided to pre-sprout all of my tubers! Apparently the disease doesn’t necessarily show on the dormant tuber. Luckily, I wasn’t too hung up on the Great Silence variety, either, so I’m not too sad to have to toss it. But I have to say, now I’m freaked out. Every dahlia I plant for the rest of this year will be checked, just in case. Yay for being a first time flower gardener 😛

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