A how I do it article by:

Don McAllister

Longmont, Colorado


This is how I grow dahlia seedlings. 

It is not the only way to grow seedlings, but it works for me.

Click on pictures for larger view.

Seeds are started in 12 x 24 cell seed starting inserts.  Cells along the edges are not planted due to tendency to dry quickly.


I use Scotts Potting Soil for Seed Starting and plant one seed in each ¾ x ¾ x 1 in (2 x 2 x 2.5 cm) cell.   (220 seeds per tray)

Seeds are lightly covered with starting mix and top is misted with a spray bottle.

Insert is bottom watered and top side is covered with bubble wrap (bubble side down).  Tray is then placed on the shelf of a plant stand where it gets bottom heat from the lights  below.


NOTE: The bubble wrap creates an evenly warmed and moist environment for germination and in 3-5 days the sprouts will be  pushing up the bubble wrap.  Remove bubble wrap at this time.

Misting and watering should be continued as needed and in 4-5 weeks the seedlings are ready to transplant on.  During this period I provide 14hrs of fluorescent lighting per day.  More information on lighting is available here.

This   view of the underside of the seedling insert shows vigorous root growth giving a good indication that the seedlings are ready to be transplanted into a larger home. 

At this point seedlings will be transplanted into Jumbo six packs where they will remain until they are set out in the garden.

The Jumbo six packs are approximately 5 ¼ x 7 x 3 ¼ in  
(13 x 18 x 8 cm) and 6 six packs fit into a standard nursery tray.

The Jumbo six packs are filled and smoothed to the top with a potting mix.  I use Miracle Grow potting soil, but any commercial mix should work just fine.


However, for best results use fresh out of the bag potting mix. Non-collapsing transplant holes are not easily formed in potting mix that is too dry.

In order to make planting holes that do not collapse the potting soil in the six packs must be well tamped.


I have found that a little tapping with the bristle side of a dust brush will create a much firmer soil structure than pressing down with the bottom of another six pack. 

About those transplanting holes.


I call it the digital dibble and I suggest you wear a finger cot or an exam glove when you are dibbling.


And, if your soil mix is too dry, you won’t be able to dibble good planting holes no matter how well you have tamped the soil.

For ease of transplanting, the insert the seedlings have been growing in is removed from the tray and placed on a shelf at a height where hands can comfortably  reach both underneath and above. 


Actual transplanting is done by pushing the seedling plug up out of the seed starting insert with a pencil.


At this point the first or "false" leaves called the cotyledon leaves have served their purpose and can be removed.

The nicely formed seedling plug fits easily into the planting hole minimizing root damage and transplant shock.

Gently push the plug down into the planting hole and firm the soil in and around the stem.


Then dibble another hole and …



When you have transplanted about half of the plants in an insert gravity starts to assert itself.  So, just turn the tray around, place a brick on the empty end and continue on.

After transplanting, water the six packs and get the plants under lights again.


Plants will move outside into sunlight in another 3-4 weeks and then on into the garden in late May.


Note that trays are raised as close as possible to the overhead lighting and then lowered as the plants grow.

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