Our annual end-of-summer contest is here, come on down to the Dave's Garden County Fair!

Dahlias and black walnut

Shenandoah Valley, VA

Can anyone tell me if dahlias will do okay planted near a black walnut? I can't find anything online that tells me whether they're harmed by the juglone put out by the walnut trees.

Aptos, CA

My dahlia patch is about 100 feet from a gigantic black walnut...they do great!
How close to your tree will the dahlias be??

Thumbnail by sudhira
Shenandoah Valley, VA

A lot closer than that - about 20 feet maybe 25. I think 80 feet is the maximum affected area for juglone.

Stanford, CA(Zone 9b)

I have some about 20 feet from a black walnut and they do fine. That's about 20 feet outside the drip line.

Temecula, CA(Zone 8b)

I think you'll find that walnut litter is more toxic to the dahlias than the allelopathy of juglone secretions from the root system. A good mulch layer of something other than walnut litter would probably be all you need to plant them within the root zone although for the sake of experimentation, try planting one that you can spare right at the dripline and then plant the others inside of the dripline as doss has said works. Juglans californica (nigra) is a heavy emitter of juglone, so most other walnuts would be less toxic than the California black walnut.

If doss says it's working for her I would plant my most precious things out of trust in her judgement. Worm castings or just plain old store bought mulch will work and do your best to keep the litter from the tree from getting too thick. Another solution might be to incorporate a little steer/cow manure into the bed as it will help to digest leaf litter more quickly, thus rendering the juglone issue moot.

best of luck to you,

Shenandoah Valley, VA

Thank you so much. I've had no luck getting any info anywhere. I've scoured the internet, even called the local cooperative extension today. They had no clue.

These are standard juglans nigra. Virtually nothing from the tree falls into this flower bed but I've had a lot of plant losses there. I assumed after I learned about juglone they were caused by the trees. The trial and error method is killing a lot of plants.

Aptos, CA

Well, I have read whereby drainage can play a key roll as well ... if the drainage is exceptional, then there is less change of toxicity...I haven't had any trouble so far...gosh now I worry, I had NO idea about walnut toxicity...my patch has had no problems! Goodness

Binghamton, NY(Zone 3b)

Hello Hart, Can you please give me an update on your dahlias? As the black walnut tree in my neighbor's yard grows, I am losing more and more plants, climbing roses, lilacs, viburnum. My rhubarb is the latest casualty. I am thinking of putting dahlias where the rhubarb was.

Does anyone have suggestions for plants or bushes that thrive near black walnuts?

Shenandoah Valley, VA

The dahlias I planted in that bed never even emerged.

There's a good list here:

But I've found the lists aren't always accurate. Some plants may struggle along for two or three years but never thrive.

What has done well in that bed, which is less than 10 feet from two black walnuts but gets plenty of sun, or in other areas near other black walnuts:

obedient plant - physostegia
lamb's ears
sedum Autumn Joy
chrysanthemum Clara Curtis
gooseneck loosestrife - lysmachia clethroides
doronicum - leopard's bane
goatsbeard - aruncus
Japanese mondo grass
lady's mantle - alchemilla mollis

star magnolia
so far, any type of ornamental or wild cherry tree
fringe tree - chionanthus virginicus

Hope this helps.

Binghamton, NY(Zone 3b)

Thanks Hart, for that useful list. It kinda makes up for your death knell for my dahlias. What a great website this is. I just joined this morning to ask my question, and it has helped me already.

Shenandoah Valley, VA

I forgot to add the hellebores to the list. They have done well too. And tall phlox. Two of my favorites so I don't know how I forgot them.

Binghamton, NY(Zone 3b)

Hello Hart, Thanks again. Tall phlox is an excellent idea, I would certainly love to see your garden. I have a city garden and not a lot of sunny space. I am trying to juggle dahlias, rhubarb and bonica roses, three long standing garden fixtures. I cannot bear to part with any of them. Now that I know that rhubarb and dalhias are not compatible with black walnut, I am wondering about the bonica roses. I have learned that rugosa roses work. Perhaps I will give it a shot, as you did with your now demised dalhias.

Strasburg, VA(Zone 6b)

i have found that my daylilies have done fine with the black walnut.....looking at a lot having been planted within the last year and are thriving with their growth so far this year....i've heard that clematis are fine and i'm testing that, most bulbs, wisteria (again, testing that this year), lung wort, hostas, decorative grasses, coral bells, lilies of the valley, trying ragwort, ferns, i have a mis-identified sedum that is happy, spiderwort, butterfly bushes, sweet william, elderberry, bee balm and bleeding heart.....many are in very close proximity and all are within the drip line....i also have crab apple trees that are doing well.....good luck :-)

Stanford, CA(Zone 9b)

Just read this and wanted to say that the dahlias are planted about 20 feet outside the dripline. Sorry for the confusion.

Aptos, CA

Hi All,

May dahlia patch grows quite near a huge black walnut tree...no problems here. However I feel you might need faster draining soil to help leech out any of the juglone. Also there is a surplus of walnuts and walnut leaves around the patch, no problems.

Strasburg, VA(Zone 6b)

good to know :-)

Shenandoah Valley, VA

Lynda, their black walnuts in California are a different species than ours, juglans hindsii not juglans nigra, and may not be quite as virulent with the juglone.

I think I'm going to just get another sacrificial dahlia, plant it and see how it does. The ones I planted in 2006 never came up at all so I'm assuming they were zapped by the juglone.

Strasburg, VA(Zone 6b)

ok....i will wait for the results of your sacrifice......now, for a juglone-free sunny location.....

did figure out a location for azaleas.....woohooo!
near pines and away from the black walnuts!

Post a Reply to this Thread

Please or register to post.

Upload Images to your reply

    You may upload up to 5 images