Yeah Spring!! Time to check the Dahlias!
March is a good time in my zone (4b) to start inspecting and dividing my dahlias that have been in storage.
In the fall, I dig the tuber clumps out of the dirt and let them dry out, rub off the dirt and store the whole tuber clump in large Rubbermaid totes covered with sawdust. I store them in our slightly heated storeroom at 45 degrees.
When I inspect each tuber clump, I'm looking for mold, mushy or rotted tubers which means they have been too wet. This information tells me that I either put them in storage before they had a chance to dry off or they froze and thawed while in storage. I cut those bad tubers off and dispose of them.
If tubers are shriveled AND dried up, they have been too dry in storage. This could be because the sawdust was too drying or the tuber sat out too long in fall, drying them out. However, slightly shriveled tubers are ok, they will plump up with moisture. I cut off and dispose of any dried up tubers as well.
The exciting part of inspecting is looking for any eyes that have become apparent. Eyes are little bumps or sprouts on the tubers where the tuber will eventually grow from. (See eyes in picture below.)
Seeing these eyes makes it easier to divide in spring.
Dividing dahlia clumps
When dividing dahlia clumps, look for an eye on the top of the root clump near the stem. In spring, the eyes become more prominent and some even begin to sprout as shown above.. It's always exciting to see that happening and makes dividing so much easier.
Each tuber needs a body, neck and eye to be viable.
Using a sharp sheers, cut the tuber with an eye from the clump making sure to leave a bit of the stem with the eye.
What to do next
You have 3 choices when it comes to planting tubers.
- Plant out
In my experience, I have found a potted dahlia takes about 3 weeks to grow a sprout and begin forming roots. I start potting them up mid-late April so that I have good shoots and roots established for going in the ground Memorial Day weekend.
- Look for the eye on your tuber. The eye gets planted up - not in the dirt.
- Make a label for your pot if you have more than one variety.
- Fill your container 3/4 way up with slightly moistened fresh potting soil - I like to use PROMIX from Menards.
- Or you can lay them flat in a tray in 2 inches of soil - with eye facing up.
- Water them sparingly, letting them dry out between watering, they do not like to stay wet.
- It is best to place them near a window or under grow lights. I have found that I do not need heat mats for pre-sprouting as long as my inside temp is 70 or above.
Propagating is a great way to increase your stock of a dahlia after you've potted up your dahlia (from one of the ways above). Once your dahlia has a 3" sprout (or 2-3 sets of leaves) you can cut the sprout off at the base and plant it. This will cause roots to grow and you have a whole new dahlia!
- First, I prepare a cup or seed tray with moist but not wet soil. Don't forget to label your container - I may, or may not have forgotten that once or twice! 🤦
- Use a sharpie to make a hole in the soil where the cutting will go.
- Using a sharp, clean razor blade, trim off the shoot making sure to cut a bit of the base tuber with it.
- Dip the end of the shoot in rooting medium and immediately put it in the hole and cover with soil. The hole helps keep the rooting medium in place on the shoot so when you stick it in the dirt, the hormone doesn't fall off.
- Place the pot on a heat mat under lights. The heat is only needed for a week or 2, until the sprout has established it's own roots.
- After a few weeks, give a little light tug on the shoot. If it comes up out of the soil, it has not grown roots. Give it more time. If it does not pull out of the soil, it has roots! Time for a happy dance!
- Make sure to water sparingly as they do not like to be wet.
It takes a bit for them to regrow roots so be patient.
3 weeks root growth on propagated dahlia.
Whether you have a pre-sprouted tuber, a propagated start or a tuber you just purchased, there are a few things to know about planting out.
- Dahlias require 8 hours of sunlight a day and well-drained soil.
- They are a warm season annual. Wait until your last spring frost date to plant out.
- Dahlias should be planted 12-18 inches apart.
- Dig a hole 3-4 inches deep and sprinkle a little bone-meal at the bottom of the hole. Plant the tuber laying on it's side. Or if you have a start with roots, dig a hole deep enough for the root ball. If you have a tuber with no shoots, it's fine if you can't see the eye - it will find it's way up.
- Cover with soil and do NOT water until you see sprouts coming out of the ground. Over-watering will cause them to rot.
- Begin watering once leaves have emerged every 2-3 days or as needed based on soil and precipitation.
- Pinch dahlia once they are 12-18 inches tall, cutting back to 4-6 inches from the main shoot. This will encourage dahlias to grow more and taller stems.
- Dahlias need support. Use a tomato cage or individually stake them, or provide a corral with twine and stakes.
- Slugs love dahlias. Sluggo Plus is a great organic option to help manage slugs and earwigs. Aphids can be sprayed with a mixture of dish soap and water (one tsp dish soap to one bottle water).
Harvest dahlia blooms early in the morning or later in the evening when it's cool. The more stems you cut the more the plant will produce.
Place cut blooms in cool water and enjoy!