I have never grown them myself, but there was a house near me that was literally filled with them for many years. The elderly man did nothing but grow the biggest dahlias I have ever seen. He did dig them up in the fall. When he died the property lost all it's glory.

Hi,

I grow dahlias from tubers every year. I live in the higher elevations in Colorado Springs and they grow fine so Denver shouldn't be an issue.

When looking at dahlias, the dinner plate sized ones look so gorgeous but think about howm much wind you might have. If you are not growing in a wind protected area, keep to the BB sized ones or smaller. That's 4 to 5 inches across the flower head.

Only plant about a week to 2 weeks before the last frost. And if you buy a plant instead of tuber, don't plant out until about 2 weeks after last frost date. Plant at the same time as the zinnias as dahlias are NOT frost hardy.
And they are a full sun plant.

I think that you are supposed to plant about 6" or more deep if you plant bare tubers but dahlias like a warm soil so I generally only put them down about 4 inches. Amend with a little bone meal mixed into the soil. You plant eye side up since the shoots come from the eye. They will probably have a little growth on them already to just gently place the tuber horizontally in the hole with the little growth side up.

If you are growing dahlias that get taller than about 2 feet, you will have to support them a little. Either put the stake in when you plant the tuber (if you put it in later you risk puncturing the tuber) or cage it in a smallish tomato basket. I use the smallish tomato basket for 2 reasons. I have dogs that love to rough house and the basket holds up better to abuse. And the basket reminds me not to plant around them. And I defintely have the tendency to plant something anytime I see bare soil. The bush will grow through the basket and soon you won't see it.

Water the soil gently and then don't water again until you see the first growth above ground. Too much water will rot a dahlia tuber and they are quite drought hardy. Also, do not mulch on top of a dahlia - remember that they like warm soil. I also don't plant anything on top of them. They will grow into major bushes.

When you have 6 to 8 true leaves, pinch back the main shoots to 6 leaves. This will make your dahlia bush out.

In Colorado Springs, dahlias come into bloom in August and are gorgeous until the first hard frost. I dont' do much extra fertilizing - I assume they get a little from the surrounding plants that I do fertilize but I don't hit them with anything special.

After the first killing frost, wait a few days and lift the tubers for next year. I have medium luck with overwintering the tubers. I think it is mostly because I don't put a whole lot of effort into trying to keep them. My old neighbor lifted hers, labeled them each and stored them in peat moss in a cool dark basement. If I remember to lift them, I put them each in a brown paper bag in a cool dark basement. See what I mean about lack of effort? :)

I grow dahlias because the deer won't eat them and they generally have few pests. Some years are better than others - the hot sumers are great - the wet cold summers are not good.

Good luck, Nancy

I'm in Central Colo Spgs and grow dahlias with great success.
I agree with all Nancy said, but I do one thing differently.
I pot up my tubers in March and let them sprout in pots.
Then I plant them out in mid May or so.
I think I get earlier bloom this way.
I use tomato cages too.
As for fertilizing, I just sprinkle some Osmocote around them when I plant.
I'm lucky enough to have a Winter greenhouse to store them in.