Thursday, November 02, 2006

My tree dahlias have buds!

A few years ago, a friend in San Francisco mentioned he had pruned a "10 foot tall tree dahlia." I shot back in a know-it-all tone, "There's no such thing as a tree dahlia. That's insane. It must be some other genus that has dahlia-like flowers." One tends to become a skeptic after learning the hard way as a budding gardener that there's no such thing as an "air fern" or a "tree tomato". A quick flip of the Western Garden Book and I was eating tree dahlia crow. A tree dahlia really is a dahlia. Dahlia imperialis. It can grow to a whopping 12 feet. Who knew? Not even this someone who aced several plant i.d. classes in college.

Two years ago, I saw... and touched... and photographed... my first tree dahlias in Mendocino, CA. On a coolness scale of 1 to 10, tree dahlias are a 10. I had to have one.

Last December I put out a query on GardenWeb re: tree dahlia sources and on whether or not anyone grew them in hot-summer, cool-winter Sacramento. Towering tree dahlias, with their striking pink (or white) blooms, are not common in the Sacramento area. In fact, I've never seen them for sale at a local nursery and I've never seen one growing and about to bloom in a local garden. Until now. In my garden!

A generous gardener from Calistoga offered to swap with me. He got starts of my 'Tropicanna' Canna and I got hefty stem cuttings of pink Dahlia imperialis. I was encouraged by the fact that Calistoga gets nearly as hot in the summer as it does here and if this man's tree dahlias thrived despite summer heat, then they stood a chance in my garden. I found a sheltered spot in the yard where they'd get sun most of the day but would be spared in the late afternoon. Because they were up against the house on the south side, they'd also be protected from strong north winds.

A previous attempt to grow tree dahlias from cuttings shortly before my GardenWeb exchange was a failure. A dear friend and fellow plant addict with the most kick-ass garden on the planet gave me a couple cuttings from her brother via a friend in San Francisco. For some reason, I decided to start my cuttings in my greenhouse, in sand. Not successful. My friend planted her starts in containers using regular potting soil and her tree dahlias are now in their second season and are neck-achingly tall, but with no flowers yet. All I can guess about why hers haven't bloomed yet is that the cuttings she started with were small compared to the whoppers I got from Calistoga. Or... is it divine justice for all the flowers blooming in her yard that aren't in mine?

Nah... probably just

Bigger stalk cut closer to the base = more nodes rarin' to grow

When I saw buds on my plants, I figured it'd be a good idea to apply some Fox Farm Tiger Bloom since I couldn't remember the last time I fed them. In fact, I probably hadn't, at all, ever.

Stem cuttings of tree dahlia resemble bamboo. I was instructed to plant them horizontally in containers. Shoots arise vertically from horizontal nodes on the stems. My plants are still in 5-gallon containers but when it's time to cut them back in December, I intend to plant the potted tubers in the ground and will stick a few new cuttings in pots in case my soil proves to be too heavy for good in-ground growth.

I hope to be able to share cuttings with friends and family who haven't yet been invited to join the church of the tree dahlia. I always find myself saying, "This plant is so cool. You have to grow this." Plant evangelist, yep, that's me.

If you want to try growing tree dahlias in northern California or beyond, check your local nursery; Kudos to any nursery carrying collector plants like this. You might also try your local dahlia society, and I certainly recommend online plant swapping through GardenWeb's Plant Exchange or Dave's Garden! Annie's Annuals sells the double white form and the pink form, by the way. In fact, tree dahlias might not be considered such a big deal in the bay area and other parts of the coast. Still... a dahlia... up to 12 feet tall? Dang!

Just came across the following link while doing a search for photos of the stalks. It's an ebay dealer in San Francisco that sells all kinds of strange wonderful things, including Dahlia imperialis. Hey, guess what the business name is? They have a great photo of the base of a mature tree dahlia plant. Also, they say a tree dahlia can reach twenty feet! OMG.

Ok, here's the official Sunset Western Garden Book entry on D. imperialis--

D. imperialis. TREE DAHLIA. Zones 4-6, 8, 9, 14-24. Multistemmed tree grows each year from permanent roots to a possible 10-20 ft. tall, 4-6 ft. wide. Daisylike, 4-8-in.-wide lavender flowers with yellow centers bloom at branch ends in late fall. Leaves divided into many leaflets. Frost kills tops completely; cut back to ground afterward. If tree dahlia were longer blooming or evergreen, it would be a valued landscape plant, but anual dieback relegates it to tall novelty class. Available from specialists; seldom sold in nurseries. Grow from cuttings taken near stem tops (or from side shoots) in fall; root in containers of moist sand kept in a protected place over winter. Or dig root clump and divide in fall. Give full sun or partial shade. D. excelsa, D. maxonii are similar.


  1. I can't even get regular dahlias to grow here, Angela, so why am I drooling over your tree dahlia? It's totally covetable, that's why! Congratulations!

    Annie at the Transplantable Rose

  2. Annie, I'm sure there are amazing plants in your area I will never be able to grow. At least we get to experience vicarious garden thrills through each other's blog entries, right?

    We even get to experience summer in winter through our Australian blog friends!

    I'll keep you posted on my buds. Fingers crossed that they take a big drink of fertilizer and burst open.

  3. Anonymous11:05 AM

    I was surfing the internet looking for things to plant in my garden this fall, and stumbled across your page. I was shocked to see the very same plant that I had been wondering about in my garden for a while. It just started growing, and this morning i noticed these beautiful flowers... and sure enough, it's a tree dahlia. Right now it's EASILY 10 feet tall, if not more. I live in Santa Cruz, and it seems to be growing beautifully. I'd be interested in more information on how to cut off the stems to plant them in pots (I'm a VERY amatuer gardener) and make them grow successfully. If you have any info on this, can you email me at Thank you so much for sharing this information! - Steph

  4. You're very lucky, Steph! As for propagating tree dahlias, the best I can find right now is a smattering of online info. I hope to be able to demo the process in December, either through pictures or video. It'll be my first time, though.

    I do know that you want to select a section of stem with at least two nodes and plant horizontally. I believe you typically get two shoots per node.

    A quick Google search yielded this advice:

    -- After flowering, cut the plant back to within 6 inches of the ground and mulch well. Mulching probably isn't necessary in mild climates.

    -- Planting depth = 8"

    Additionally, you can check GardenWeb threads. There are a few threads that list successes as well as failures.

  5. Anonymous3:03 PM

    We moved into our house in Salinas a year and a half ago, inheriting a tree dahlia in the process. I thought it was a large weed at first, then got it identified by sending a picture to Dave's Garden. It grew to about 10 feet last year but had a pretty wimpy crop of blooms -- only 3 blooms on 2 stems. This year it's grown to about 12 feet, with at least 4 stems showing multiple buds. Only trouble is, you have to get on a ladder to take a picture of them! Cutting them back after they bloom and mulching around the base seems to work well. They also seem to like lots of water.

  6. I love your story and thought you might get a kick out of mine. I'm a college student from San Francisco. A few years back my mom asked me to cut back her tree dalia's. I did a bit of research and found it's best to cut them back in December almost all the way back to the bulb. I did so and tossed the long stalks to the side. To my surprise little shoots started coming out of the nodes! I planted them and now have tree dalia's popping up all over the yard, the most impressive is a second year bloomer that is over twenty feet tall, even taller than the original bunch they came from! Amazing!

  7. Anonymous1:55 AM

    Well, here goes, my very first blog might just as well be about something beautiful. I am in Perth, Western Australia, coastal limestone pure sand soil and am most proud of my tree dahlia. It is currently looking lush and lovely at over 2 metres tall (over six feet). It was given to me as a growing cutting from a friend and now mine is far better than the parent plant. Lucky me! We are mid summer with daily temperatures over 30 Celsius (from memory, that is around 100 degrees Fahrenheit) and quite windy. Happily, my front garden is fairly sheltered from the wind but not the heat.

  8. Anonymous5:03 PM

    Hi Anonyymous from Western Australia, I am wondering how your tree dahlia is going this year after the big nov. eat wave. I live in Castlemaine in Central Victoria, mine are growing in a large courtyard surounded by 15 feet walls and have been up once this year 2009, and now have risen again in Nov. after 40c degrees. The cuttings I layered have not taken. I layered them about July. Can you let me know what yours are doing know please.Thanks

  9. I recently moved into a house with the mysterious tree dahlia in the yard. In my experience, there isn't much you can do to kill these beauties, I live on the San Francisco Bay and the dahlia in my yard is green all year long. It has bloomed almost constantly since last August and is my new favorite plant. I have several in my yard and the base of one is easily 4" in diameter.

  10. Anonymous7:43 PM

    I love all of your comments here. I live in Santa Cruz on the (upper) West Side. I JUST got some White Tree Dahlia cuttings from some ppl here on the West Side and am VERY excited about what's going to happen. I hope I am successful in my attempt to get them growing. I'm a pretty successful gardener in general, so I'm hoping for the Best.

  11. Anonymous3:41 PM

    I live in the far north of scotland and i have just seen these gorgeous tree dahlias tonight for the first time ever and they are absolutely stunning,I dont know if they would grow over here but i would love to try and grow them,but i am doubtful of getting the plants in this country,i haven't seen them anywhere but will be keeping a look out for them,Dahlias are my favourite flowers and i grow them every year with a lot of success and i leave the tubers in,I plant them deep enough so that the frosts dont kill them off..