Dahlia-Growing Q&A from Instagram
Gorgeous mix of Peaches N Cream, Silver Years, Wizard of Oz & Cafe au Lait dahlias.
February 27, 2024
Instagram Community Q&A!
You asked about dahlias and I’ve answered — for more help, see the list of my entire Dahlia Growing Blog Archive.
best way to support dahlias (how to make them stand up straight) as a home grower (shealyn)
When growing dahlias at home, individually staking them with bamboo stakes and biodegradable twine is the best way to go. You could also use metal u-posts or another type of wood stake. To stake dahlia plants, simply stick the stake into the ground right next to where you planted the tuber. You can begin tying the dahlia stem to the stake when it grows to be 18-24” height. Tie the twine so there is still room between the stem and stake so the plant can move around and keep growing.
Also, make sure you plant dahlia tubers in a 6-inch deep hole so they grow deep roots, which will help them from falling over.
how to prep new raised beds for dahlias and what soil blend to use (alicia)
When growing in raised beds (beds that have been supported with wood, stones or other material on the sides so extra soil can be piled up), it’s important to use a high quality soil mix. I would suggest finding a local nursery near you that offers top soil and compost delivery (in Western New York, check out CJ Krantz). You’ll want a blend of top/garden soil (50%) to compost (50%). Compost can be derived from residential waste, mushrooms or animal manure, but I would beware of free municipal compost sources.
If you do not have a local source for top soil/compost delivery, you could buy these materials in bags at a garden center (it will cost more). Look for brands like Dr. Earth, Fox Farm and Coast of Maine. Avoid brands like Scotts and Miracle-Gro: read why those brands are bad here.
To fill your raised beds, simply add the top soil and compost in layers until you reach the top. Over a few weeks, the soil blend will settle and sink a bit, so overfilling is not a bad thing. I would also recommend adding dead leaf litter from your yard to the mix, if you have any lying around. This will add wonderful organic matter to the soil for soil life to begin decomposing into usable nutrients for your plants.
if we’re making a new in-ground growing bed for dahlias, should we add anything to the soil? (jessica, emilee)
Yes — I always amend the soil at the beginning of Spring with a 1-2” layer of compost (delivered or bagged), a sprinkling of alfalfa meal (or pellets which are sold as horse food), and kelp meal per package directions, to my dahlia patch before broadforking the soil deeply. The act of broadforking can also be accomplished with a simple garden fork. Then I plant into that with a small handful of bone meal for each tuber. If you add this nutrition up front, you won’t have to fertilize during the year.
It’s important to understand that plants suck up nutrients from the ground every year, so you must add back to the soil what they take away, for your soil to stay balanced and nutritious. A soil test can help you understand what nutrients are missing (I send soil samples in to Logan Labs in Ohio for $25 plus cost of shipping). Adding shredded leaves to the top of your garden at the end of every season will also help replenish nutrients and add wonderful organic matter. Learn more in this blog post about Fertilizing & The Law of Return.
what to fertilize dahlias with, and how often? (ally)
If you follow the soil prep instructions in the above question (using compost, alfalfa meal and kelp meal to amend the soil in the Spring) then you won’t need to fertilize your dahlias at all during the season. For lots of blooms, you should plant each tuber with a small handful of bone meal straight into the planting hole. Keeping dahlias watered, especially during droughts, is also important for the plants to stay healthy and producing the most blooms.
On our farm, we do a biweekly spray of our own homemade concoction of compost tea (recipe can be found in this post). I don’t consider this a fertilizer — I consider the compost tea as a vehicle to add microbiology to my dahlia plants so they can work to fight diseases and add more nutrients to the soil by breaking down organic matter. To understand more about soil microbiology and the role they play in providing nutrients to plants, read this post here.
what are some favorite varieties for cutting with longer vase life, sturdy stems and prolific blooms? (sarah)
Ball-type and decorative dahlias tend to have the longest vase life of all the dahlias. My favorite varieties that fit the bill for all of those criteria above are: Diva, Clearview Peachy, Maarn, Brookside Snowball, Blizzard, Linda’s Baby, Rose Toscano and Wine Eyed Jill.
i take my tubers out of storage early to try to take cuttings but they grow too slowly (sarah c)
I do not have personal experience with growing dahlias from cuttings, but I know that it does take a long time to grow a dahlia plant from a cutting (a dahlia “cutting” is growth that has been cut off of a tuber that has been forced to sprout early, and planted into soil to produce an entire new dahlia plant, for those who are unfamiliar). I would recommend starting cuttings at least 12 weeks before planting out. Cuttings will grow faster if you have them in optimal conditions with heat and lots of light. Grow cuttings in a warm 75 degree room (use a space heater if needed), under bright LED lights like these. Treat your cuttings as you would when starting seeds indoors.
best time to dig up dahlia tubers and bring them in? (adrienne)
Dig dahlia tubers after your first frost, once the upper parts of the plant have turned black (cells have died due to the cold), but BEFORE the ground freezes. The timing for this is different every year. Here is a really helpful post on When to Dig Dahlia Tubers with more info.
best way to overwinter dahlia tubers? (adrienne)
I overwinter thousands of dahlia tubers every year in my basement with the tubers packed in wood pine shavings and plastic storage tubs. Here is a detailed tutorial with things to consider for your personal space: How to Store Dahlia Tubers in Wood Shavings.
how to keep thrips away from dahlias? (sarah c)
There are two major ways we can keep all insects, including thrips, at bay. Thrips are abundant in the environment but, just any and all bugs, they will only eat plants that are unhealthy and already on their way to decomposition, believe it or not! So, the first step to deterring thrips is making sure your dahlia plants are as healthy as possible so they don’t get eaten because healthy plants are literally unpalatable to insects. First, ensure your soil is adequately balanced with proper nutrients (see soil prep questions above) and taking steps to increase soil microbial life will increase nutrient exchange in your garden and will make your plants healthier, thus, less susceptible to any type of insect damage. It is also incredibly important that your dahlias have adequate water supply, especially during droughts. Inadequate water supply will cause plants to shut down and weaken out of desperation and will become more susceptible to bug damage.
Second, you should take steps to increase your beneficial/predatory insect population. Do this by completely removing any chemicals from your garden (pesticides/herbicides), then plant a wide variety of different plants to attract a wide variety of different types of beneficial insects. With a high population of lacewing bugs, soldier bugs, pirate bugs (and other funny named bugs), they will keep thrip populations under control by eating them, without a need for your intervention. This methodology of insect control is known as Integrated Pest Management.
Highly effective native-to-U.S. plants for attracting beneficial insects are: Yarrow, Mountain Mint, Ironweed, Goldenrod, Echinacea, Butterfly Milkweed, Swamp Milkweed, Penstemon, Wild Bergamot (bee balm), Serviceberry, Elderberry, Chokecherry, Ninebark, Dogwood shrubs.
what companion plants for zone 6? (chantal)
For a home garden, companion planting can be a lovely way to incorporate more beauty into your dahlia garden. To help keep weeds down, you could direct seed Sweet Alyssum right on top of the soil, right after planting your tubers, and it will grow as a living mulch and attract beneficial predatory insects.
You could also consider planting perennial edible herbs — my home dahlia garden is bordered by ‘Grosso’ lavender, which gets big and lovely flowers, and I also have sage, thyme, basil, parsley and dill among the dahlias, which all produce more dainty flowers that contrast nicely against the rich, bold dahlia blooms. Herbs will also deter bunnies. Richters Herbs is a lovely source for a lot of really unique flowering herb plants that are hard to grow from seed. Additionally, here is a post on Herb Gardening for Zone 6.
differences between planting dahlias in-ground vs in pots? + info for growing dahlias in containers (emily + katie)
Growing dahlias in the ground vs. in pots/containers actually is different. It’s important to understand that all plants have the ability to access nutrients and water that lie deep in the layers of ground soil, whereas plants that are grown in pots/containers can only access whatever nutrients and water are available in that pot or container.
So, when you’re growing dahlias in a pot/container, you will have to fertilize and water them more often. They will require more attention from you, to grow robust with beautiful blooms; however, it is totally possible and if that’s the only space you have, I highly encourage you to give it a go!
Some tips for growing dahlias in containers:
The bigger the pot/container, the bigger the dahlia will grow (recommend no smaller than 12” x 12” approximate size per dahlia tuber). This type/size of container would be perfect for growing dahlias. See the 2nd question above for instructions on how to prep soil for a raised bed, which is how I would approach prepping soil for this type of container.
You should entirely change out the soil or heavily amend the existing soil every spring. This is because the plant will have sucked up most of the nutrients from the soil during the previous growing season and not much will be left for it to scavenge. You can improve container soil by removing half of it and replacing it with compost, and adding alfalfa meal, kelp meal and bone meal into the mix. If that is too much for you to purchase, you could settle on amending with just bat guano (yum!)
Pots will need to be watered every single day in the hot season. Yes, every single day! Make this easier on yourself by setting up a sprinkler or soaker hosing on a timer.
last year I grew dahlias in containers and by august they were dying from the root up (colleen)
It sounds like your dahlias were either severely dried out or suffered from some sort of disease — I cannot say without a photograph. To prevent dying from lack of watering, setting up a soaker hose on a timer (2x/day morning and late afternoon for 10 mins if growing in containers), will keep them alive.
do i have to start dahlias indoors? or can I just plant tubers outside after last freeze? (kirin, colleen)
Planting dahlia tubers directly into the ground is the best way to plant them! It’s how I plant my entire field — I do not start dahlias indoors before planting. Simply dig a hole and plop it in. For best results, follow the garden prep instructions in this post.
do you soak dahlia tubers before planting? (colleen)
No — do not soak dahlia tubers in water before planting, this can cause them to rot in the soil.
how to protect dahlias from deer and bunnies? (katie)
In my experience, deer generally don’t eat dahlias, but they will if they are super hungry and have nothing else to eat. If you have deer in your yard, consider planting them their own deer food forage plot with these seeds that you can just throw onto bare ground. The concept is, if they have other stuff to eat then they won’t bother your dahlias (which is why I think they didn’t eat mine, before I had a professional fence installed). Otherwise, there is a company called Deerbusters that sells good DIY deer fencing kits that I used on my first flower farm.
Similarly, bunnies in my backyard do not eat my dahlias — and I have an entire family of bunnies. My dahlia garden has a thick border of ‘Grosso’ lavender around it, which the bunnies don’t like the smell of. I’m not sure if this entirely keeps them out, or if they’re genuinely disinterested in the dahlias. Regardless, the best material to keep rabbits out of the garden is putting up a simple fence using 1/2” hardware cloth and metal u-posts, secured together with strong zip ties. I suggest hardware cloth instead of chicken wire because chicken wire is super flimsy and will just become loose and fall over in a few seasons.
are any of your varieties considered waterlily? (justine)
Not technically, but I do have two decorative varieties that take a lovely waterlily-looking form: Nicholas and Silver Years!
how to identify diseases on dahlias (Rebecca)
I use online resources like this one to help identify pest and disease issues on dahlias!
how do i get a glacier to come through quick and give me nice loamy soil? (michael)
hahaha. Thoughts and prayers? Seriously though, if you try adding a thick layer of shredded leaves to your beds at the end of every growing season and broadfork it in with a bit more compost every Spring, it will help break up hardpan and gross city soil in a few seasons’ time.
why are they so pretty though? (jess, sweet jess)
Because of the tender love and care you whisper to them in the field, duh! 🌸
