Starting dahlia seeds

calico20hill · 2023-03-05T22:07:16+00:00

I am excited to see plants growing form Rock Run Ashley seeds I collected last year. I don't think I have tried seedlings from it before. I started quite...

KitCMC

Hi dahlia friends 😊 I have a bunch of seedlings with their first set of true leaves. When does everyone typically transplant to larger pots and begin fertilizing?

SteveM

KitCMC When does everyone typically transplant to larger pots and begin fertilizing?

My seedling mix doesn't include any fertilizer so I usually fertilize at first signs of a true set of leaves. Most growers recommend fertilizing with a weak solution but I use Miracle Gro (or equivalent soluble) at full recommended strength (1 TABLE/gal) as a soil drench. The cotyledons should remain green well after the first set of leaves appear, so if they turn yellow it can be the first sign that it is time to fertilize.
Pot size: I transplant my seedlings into individual pots about the size you show (2") and grow them in those pots until I plant out to the garden (plants about 6" tall). With seedlings a well-formed clump of tubers is not important so I don't worry if the seedlings become root-bound in their small pots before I get a chance to plant out.

Teddahlia

The methods of growing dahlia seeds are the same as growing plants in general. They eventually need a bigger pot and since I always put fertilizer in the water at a very low level, they are fine. They are subject to the "goldilocks" rules of growing plants. Too small is not good and too big is not good and I like to transplant the seedling to the garden when they are about 6 inches tall.

KitCMC

Teddahlia thanks @Teddahlia!

KitCMC

SteveM That’s great to know, thank you! I was worried about their sensitivity to fertilizer. I started potting some up today.

MissyWeitzel

Every year I screw something up and 2026 is no exception. I fried multiple trays of seedlings not yet hardened off including all of my micro seedlings which I was most excited about. I set myself alarms and all that and still forgot to move them out of the sun.

So I am turning my mistake into an experiment and I direct sowed some dahlia seeds. Unfortunately I used up all my saved micro seeds but I had a lot of others left and just used ones from seed packets/parents I had really good germination from. I did 2 or 3 seeds per spot and crossed my fingers and am hoping for the best.

I have loads of older seedlings to further evaluate this year, but there's nothing like the excitement of seeing each new 1st year!

SteveM

MissyWeitzel I fried multiple trays of seedlings not yet hardened off

How badly were they burned? I have burned seedlings but, if there is any green left at all, and if the root system is sufficiently developed, I have had them come back from the laterals. I alway think I have discovered every possible way to kill dahlias but I sometimes amaze myself and find a new way.

Teddahlia

People think planting dahlia seeds and nurturing them to be big enough to plant and then survive in the garden is easy. Tomatoes are easy. Dahlias are more demanding. I have never had someone say that the seeds from the dahlias were weeds the next year. There is almost no risk that they will sprout in your garden. Having said that I know of two occasions where that happened. I remember how easy it can be if you do not label each seedling. One breeder when he started breeding sprinkled seeds onto a 4 x 4 area of fine soil and raked them in. He had numerous seedlings that he lifted to transplant elsewhere. He introduce a couple of those seedlings.

MissyWeitzel

Next year I think I'm going to harden off in trays under hoops with shade cloth. I have 40% cloth so I'll do a few days with double layer then single layer for a while.

Juliarugula

I will say, though, that I find dahlia seedlings easier to harden off than other plants, for whatever reason. I usually do 4 hours on my front porch the first day, strategically arranged/timed so they’re in shade except for maybe an hour of sun. Then the next day 6-8 hours with about half and half sun/shade time. Then the last day they just stay out there. And no special care when they eventually move to their final full sun bed. I don’t think I’ve ever had one sunburn with a simple 3-day transition.

I used to introduce tomatoes to the outdoors a lot more gently, and Lisianthus seedlings are the absolute worst.

MissyWeitzel

SteveM they were too hot in their black trays, a few were admittedly too small to try to force outside, and they burned and completely dried out and didn't revive even after watering and shade. They weren't in nice big pots.

Bessie

MissyWeitzel you are not alone. As you may remember, last year I killed about 300 seedlings. They were dying off slowly, so I couldn't figure it out. Then the light bulb moment was this year when I realized the heat mats I had put in place, right before leaving for a few days, almost surely cooked them. It explained and made sense how to death seemed random, and drawn out since the mats have hot spots.
Also, I found a clump of seeds sprouting in the ground right where one of my seedlings was planted last year, in my vegetable garden. The few seedlings seem happy enough, so I think your instinct to direct sow may be a winner. I predict you'll be surprised.

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