Growing Dahlias in High Heat
You love dahlias but you live in the land of scorching sun! What to do? Well- here’s a blog full of tips for growing with more success in high heat.
I’ve written a lot on this topic with tips on different methods for success in high heat but I’ve never compiled it into one place. Some of this will be links to past blogs (no sense in re-writing it all here) and some will be newer methods we have learned over the years. So here goes:
1. Variety is important. Some varieties just don’t work super well. I wrote about how I choose varieties in part 4 of the Dahlia Game Plan series last winter. I also have a whole module about choosing varieties in my Dahlia Growing for Beginners Virtual Workshop.
2. Watering is crucial. Several years ago I started experimenting with pulse watering. It was a game changer for keeping dahlias hydrated in high heat! I wouldn’t go back to my old method now. Read more on that here
3. Shade- Shade cloth or location- either one works. So we grow 1000’s - it’s not practical for us to use shade cloth. Would it help - Sure! But our fields are multiple places and too big to do it cost effectively. This is why I’ve worked on other methods (as listed in this blog) to give us success growing in high heat. But for smaller growing situations, shade can be a powerful too.
4. Planting time- This is really important. You need to get plants established before your climate and soil get too warm. Tubers can cook if planted in soil that’s too hot. This timing will depend on your climate. For us, it means get them done by end of May. If you have to plant in warmer soil, try a rooted cutting that’s been potted up. Those roots will establish faster and you can water it which cools your soil.
5. Surround (Kaolin Clay) - We use this as a crop protectant— helps keep early season powdery mildew at bay, keeps mites and thrip pressure lower but also cools the plants several degrees. Longer form blog on it here.
6. Pruning- Dahlias respond very well to pruning. Cutting plant back by half is a great method to employ mid summer during the really hot part. This lowers the stress level on your plants. Usually early July is our timing if we choose to cut back. This method works well if you overwinter your dahlias and don’t have control over when they sprout. You’ll get blooms again 6-8 weeks after pruning.
7. Patience- growing a plant in an enviroment that is less than desirable for it is going to take time to learn. Dahlias can thrive in a lot of places but high heat is a bit of a learning curve. So expect that it will take several years to learn how to do it successfully.
However, I hope these tips will help! Do you have any great high heat growing tips? Send them my way!
Planting Rooted Cuttings
Rooted Dahlia Cuttings are a bit different from a tuber. You are planting an actual green plant with roots instead of an ugly brown root! They both produce gorgeous flowers - they just begin differently.
Rooted cuttings are small when they first arrive. Usually only a few inches tall. Different varieties grow at different rates. You can have little top growth but a full root system. You could plant directly if you are past you’re last frost date but your chances of success get much higher if you pot the cutting up first. Grab some good potting soil and 3-4” pot. If your cutting comes in a pre-fabricated plug like a root riot or the paper contained elle pots- tease as much of that off as you can. On the elle pots, you can just cut the paper and leave it on there. You just want the roots to have freer access to move and expand. If they get restricted, this will inhibit tuber growth and causes the “mass of roots” effects instead of tubers.
Place the potted cutting into a shady/part sun place. Remember that most rooted cuttings have come out of a grow room or greenhouse before shipping and need to be hardened off first. So shady/part sun for a few days and then full sun until the roots fill the pot.
I recommend using a light fertilizer after your cuttings have been potted up for about 10 days or so. I’ve found that they use up the “goodness” that is contained in the pod or dirt they were rooted in very quickly.
Water when almost dry. It’s very easy to rot out a cutting so run it on the dry side but don’t let it completely dry out.
Well filled out pot, ready for planting
After the roots have filled the pot so that the dirt stays together when you pull it out of the pot, you are ready to plant (usually 3-4 weeks). Plant into your prepared garden bed, landscape or large pot (7 gal minimum). Remove the bottom set of leaves and plant so that the node from those leaves is underground. This will help encourage tuber growth.
Water well after planting and pay close attention to moisture levels for the next 2 weeks as it is getting established. Be careful about planting tubers and rooted cuttings near each other because of their different water needs. You can plant tubers a few weeks before your rooted cuttings (say when you pot up your rooted cuttings) and they will be at the same stage by the time your rooted cutting is ready to plant. Therefore requiring the same amount of water.
I get asked a lot about how to get good tuber growth off rooted cuttings. I’ve noticed 2 things:
1. You need to fertilize them as much as tuber grown plants. When I hear of cuttings that didn’t grow tubers, I usually begin digging into the grower’s fertilization plan (and often they don’t have one) or they didn’t fertilize enough. Tuber grown plants won’t make any or many tubers either if you don’t fertilize them. Plants need food to do their thing!
2. Not getting any tubers can also be problematic on newer bred varieties. I’m speaking from observation over a few years here. I’ve tried newer (unicorn) varieties from very reputable breeders who are not in my climate and had very poor results at first. I got the “ball of roots”. I managed to save the root balls- you can put them in a pot with dirt or store in vermiculite. You need to be sure they don’t dry out so humidity is important!! Then I made cuttings off the root balls- so year 2 I got a few tubers- small and not many but some. Replanted those tubers in year 3, got much better tubers. Year four I replanted tubers and rooted cuttings off the year 3 tubers and got good results. So my observation is that new varieties bred in different climates are going to need time to adapt.
So why doesn’t this happen with any variety that is bred in a different climate? It does to a degree. Those of us growing in hot climates know that certain varieties do better here. But also because some varieties have been around so long that their stock has literally been all over the country and mixed around so much that it acclimated.
This is purely observation, I don’t think anyone has done a scientific test on this. But over so many years of growing, I’ve noticed that varieties do adapt to where they are grown.
Let’s Get Planting!
Well, we planted our first dahlias of the season yesterday. We put in rooted cuttings of 20th Ave Memory; she’s a sweet light pink ball.
For some of you, you planted a month ago, for my farm it’s the earliest we can start and for colder regions, you are just waking up your tubers.
But regardless of when you do it, there are always lots of questions about planting. And first thing I want to say about it- Don’t Overthink It!
It’s a really simple process but people tend to overthink it.
Here’s the basic process for planting a tuber:
1. Dig a hole 4-6” deep. Deeper if you have really good draining soil.
2. Put the tuber in (lay it horizontally if you don’t know which end the eye is on).
3. Cover it with about 2” of soil, more if you have well draining soil.
4. Do you water it? Well if you are lucky enough to live in an area with consistent rain, then no. But if you live in the land of roller coaster weather like I do- you need to look at the weather report. If I see we have significant chances of rain in 2-5 days and the temps are under 80 degrees, then I don’t water. But if it’s hot and dry, then I water once- a good soaking. But that’s usually all that’s needed to get the tuber going.
Here’s the basic process for planting a rooted cutting:
1. Dig a hole ( as big around as your pot is but a few inches deeper)
2. Place your rooted cutting (that has been potted up) and place it deep enough so that you are covering 1-2 nodes on the stem with soil (remove any leaves attached to these nodes). Planting those nodes under the soil gives you more chances to tubers being made at those nodes. But you have to pot up your rooted cutting in order to get a tall enough plant to do this.
3. Water your plant deeply. Keep it well watered for the first 2 weeks while it establishes. Not sopping wet, ensure good drainage but don’t water starve it at this stage.
So those are the very basics but let me cover a few things I get questions about:
1. Planting in no dig beds or raised beds- How deep should they be? If they don’t have a bottom on the bed, then 6-8” is fine, more is okay too. If the bed has a bottom (but make sure it still has drain holes, then 810-12” is going to be better.
2. How do I plant a clump? Same way as a tuber but dig a bigger hole and make sure the old stalk is facing up ( you usually have an old stalk on these types of clumps)
3. When can I plant? After you last frost date (Google it) and when your soil has had time to warm up. If you have warm weather after your last frost date for a week or two, that should be sufficient.
4. Can I plant my dahlia in a pot? Yes, but make sure it’s at least a 7 gallon size. Plant just like you would in the ground.
Got a Planting Question, drop me a line here.
What To Do When Your Dahlias Arrive?
It’s almost that time— When it seems like Christmas comes once a week? When those mysterious packages show up and you go— I wonder which farm this one is from? Or is that just me that forgets what they ordered and from whom?!
I do love March and April because it really does feel like Christmas around here- new plugs arriving for the farm and tubers from far and wide.
But you may be wondering-What do I do with these tubers when they get here? Do I plant? Store them somehow? Well - keep reading!
Tuber order arriving to our farm
First thing to do— OPEN THAT BOX!! Don’t let it sit for more than a few hours unopened. The easiest way to kill your dahlias is to leave tubers or rooted cuttings in a box unopened for a few days. These are living things- they want to breathe some fresh air. So Open That Box!
If the box is full of just tubers, put it in a 65-70 degree place (inside your house is probably fine). If the tubers are in plastic, open the plastic up. Don’t leave them inside because they may condensate. Inspect your purchase. If you see anything odd, email the seller immediately. Good, responsible tuber sellers will get back to you within a few days. Posting in an online forum will only get a bunch of confusing answers- just go straight to the source that you bought from.
If you are within 4 weeks of your planting date outside, then place them in a spot where it’s 65-70 degrees and the humidity is on the high side - that will do just fine. Do check on them every few days. A lot of houses can be dry if you are still running your heat a lot so you want to make sure that your tubers don’t start shriveling due to dry air. If this happens, get them planted straight away if you are warm enough and soil temps are around 60 degrees. If you can’t plant outside, pot up your tubers in a small pot and water sparingly. Usually one watering to get it going is enough. Run it on the dry side so you don’t rot out your tuber.
When you have passed your last frost date and the soil is warm (60ish degrees), you can plant outside. Then you’ll have a 2-5 week wait while it sprouts. Remember some tubers are slower to wake up than others, some can take up to 8 weeks.
Rooted Dahlia Cutting
Now if you bought a rooted cutting, well- instead of writing it all out here again, I’m just going to direct you to my other blog post about what to do when your rooted cuttings arrive.
It’s not super complicated - basically it’s just remembering that these are living things and they don’t like to live locked inside a box for longer than they have too!
Rooted Dahlia Cuttings: How to: Part 2
In Part 1 we talked about all the supplies we need- Now that you have all those things gathered (you did that right??)- Let’s get started!
Tubers potted up in a tray
So we need to generate some cuttings to root. Begin by potting up your tubers. You want to leave the crown area exposed (that’s the top part where the eyes on the tuber are). If you aren’t sure where the crown is- it’s right above the skinny part of the tuber- that’s the neck. The three parts of the tuber are the body (the fat or long part), the neck (usually skinner than the rest of the tuber) and the crown (this is the part that attaches to the stem).
Remember you can use potting soil, sand, soilless medium, perlite- whatever you want to try- it just needs to be able to hold water so you get the tuber moist. It’s going to take a minimum of 2-3 weeks to “wake up” a tuber. Sometimes longer— remember that varieties that bloom later, take longer to wake up. They can be stubborn and take 2 months occasionally. So take this time into account in regards to when you want to plant out. It will also take 3-4 weeks to root your cutting.
3-5 weeks wake up time (average) + 3-5 weeks root time + 1-2 weeks to harden off = successful rooted cutting ready to plant. (add another 4 weeks if you like to pot up to a larger container after rooting) Take that time and back it up from your last frost date and you’ll know when to start.
Now- this is the point where people start asking for tubers to ship early because they realize they are suddenly “behind!” Actually, think of it like this- it’s much less stressful. Don’t worry about trying to make a ton of new plants off new to you varieties in their first year. Just plant the tuber or rooted cutting (whatever you bought)- grow it and evaluate it. Then you can make plans to expand it the next year. I find this method works really well if you are in a hot/extreme climate. You don’t want to waste time multiplying a variety if it doesn’t work well in your climate. So (like I mentioned in part 1)— patience is a big part of this process. You’ll thank yourself in the long run for taking the slow route!
You’ll need to keep your potted tubers warm- you can do this via heat mat or a heated room. If you use a heat mat, make sure you have temperature control. I’ve found too often that I end up rotting tubers this way. I switched to using a heated room a few years ago and I find that it’s a much more even heat and works better. A small closet might work for this.
After a few weeks, you’ll begin to see green sprouts. Once the sprouts are about an inch and a half long, you are ready to “pull” as we say in dahlia lingo.
Prepare your rooting medium (see part 1 for options) and wet it down. You don’t want it sopping wet. Wet enough where it’s not going to dry out for a few days. This level of moisture is going to be a bit different for everyone because of different environments so experiment a bit. After you have prepared your tray you are ready to take your first cutting. You want to firmly grab the sprout at the base right before where it attaches to the tuber, then wiggle it a bit and it will pop off. If a bit of the tuber comes off too- that’s okay. Insert the cutting into your rooting medium (if you are using a rooting hormone, this is the point where you dip it in there). Make sure the cutting is stuck in at least 1/2”- you can go deeper if it’s a taller cutting.
The cutting looks small but I’ve found that taking them at a younger stage works better- I’ve achieved more consistent results this way. Now continue taking anymore cuttings that are ready to pull. After this, place a humidity dome over top of the tray. You want to keep the humidity high during this time. Then place under lights and on top of a heat mat or in a heated room under lights.
Check your cuttings once a day to make sure they aren’t drying out. After about 2 weeks, gently pull on the cutting and see if you feel any resistance. You can also look under the bottom of your tray/pot and see if you see any roots. Once you’ve got roots, you can lift off the humidity dome. Keep growing under the lights (and on the heat mat or in heated room) for another few weeks. Once you’ve got a good root system you can either pot up into a larger container and grow on or harden off and plant outside if you are past your last frost date.
Once your potted tubers start producing cuttings, you’ll need to check every few days to see if there are more ready to pull. Once you pull the first one off, the tuber will usually produce 2 or more for the next round. This is how they multiply quickly.
Remember that rooting cuttings is all about environment so if you fail the first time, make some adjustments— try a new medium, adjust your temperature up or down. Water less or maybe more- Each environment is different so there’s no 100% full proof method (no matter what anyone says)- Each environment has external factors that are out of your control so you have to adjust around those. Keep trying- Dahlias are a great plant to teach propagation techniques. You’ll have it figured out quickly!
