When to Plant Your Dahlias Out in the Garden

Note: The Bulletins of the American Dahlia Society are full of excellent and timely information regarding successful growing of spectacular dalhias. This article, by Dr. Rick Peters, is a good example of that useful information. This article was published in the June, 2005, Bulletin. Decades of the ADS Bulletins are available for reading in the members-only portion of the website.

Whenever a new grower asks when the dahlias can be planted outside, we in the northern climates always seem to answer, “When the fear of frost is over” or “Anytime after Mother’s Day”. Actually we need to give a little bit more information to those growers.

Every region in climates that have freezing weather will publish a “Frost Free Date”. For my area in Muskegon, Michigan the date is May 15th, and this indicates that throughout many past years, 50% of the time there was a frost after this date and the other half of the years, there was no frost after this date. It sort of makes me wonder Why they call it a “Frost Free Date”. However a grower could find out this date from their Extension Service of their state University.

Last year, I started my tubers indoors and after the plants had their first set of leaves, they were moved onto two tables in a greenhouse that I rented for about 5 weeks. Putting the tubers up in pots on the first of April gave me a small 6-10 inch plant by the middle of May. A few years ago, I used to rush out and plant as soon as I could, sometimes as early as the 3rd of May. I soon found that when the plants were out in the cold nights and warm days, they really didn’t seem to grow very much for a couple of weeks. Also, I risked having to go out in the evening and cover up 180 plants if there was a frost freeze warning by the weatherman. Then uncover them all the next morning. This just wasn’t my idea of fun!

Lately I have decided that there really isn’t much of a rush to plant them in the garden. They are doing fine in the greenhouse, and the only thing to be concerned about is if the dahlia plant becomes too tall as to fall over in its pot. So it has been toward the end of May that the plants go into my garden.

Even though many of you who grow dahlias do not have access to a greenhouse, there are still a few methods that you can use to get your plants ready for the garden. Before the greenhouse availability, I grew the plants in separate 4-inch pots in the warm basement under fluorescent lights. They seemed to start pretty well when potted up on the first of April. After reaching about 4-5 inches tall, they tended to become more spindly than I would like. At that time, I put as many of the pots as I could into trays. I moved the trays outside into my patio before I left for work, and I brought them back into the house in the evening when the sun went down. This lasted for only a couple of weeks, and then they were left out all the time when the nights grew warmer. The plants got fairly robust after two weeks on and off the patio, and by the end of that time they were planted into the garden.

For those of you who wish to plant tubers directly into the ground, then you can plant after you feel the last frost has gone. Then you know that you have a little buffer, because the tubers’ sprouts will not be coming up for a couple of weeks, and they will not freeze under the ground. You do have to check to see if the shoots are coming up and check the weather advisory for frost. A light covering again will need to be in place if there are shoots above the ground and a frost warning predicted. Also, you do run the risk of a cool, wet spring that might rot your tubers before they even have a chance to sprout.

– Richard W Peters, M.D.
   Grand Valley Dahlia Society