It is common enough that the last freeze in southern Idaho happens as late as the first of June. So when it comes to getting something like tender (sensitive to frost) dahlias planted, it is a challenge. It’s one thing to plant your tomatoes a couple of weeks early, then have to run out and cover a row of plants all in one place. It’s quite another to remember various places in flower beds and deal with other landscaping.
By the time June rolls around, there is a fair amount of growth, planned and otherwise, going on in the flower beds. So there is also the problem of loosing track of where the bulbs are after you plant their bulk underground. They can end up choked out by weeds, damaged by weeding, or just neglected. This is why I have taken to jump starting my dahlia bulbs.
I start with a bag of bulbs from Costco, because it’s generally an impulse buy in March while I’m grocery shopping… boy, do they have my number. They don’t have to be planted right away, but it is a good idea to keep them in a cool dark place until you want them to grow.
Dahlia bulbs are large and strange looking, if you ask me. This means they need gallon pots to begin with. I usually have quite a few that I save from year to year. And that means mixing up quite a bit of potting soil. I still just do it a large mixing bowl and a time, because that is all I can stir at once without straining my arm!
You want to look for two basic things before you plant the bulbs. Identify the stem and look for any growth that has already gotten going. The stem needs to be pointing up, but how deep in the soil depends on how much stem there is above the dangly nodules that make up the rest of the bulb.
The growth will be sometimes be elongated, because it has been looking for light. Sometimes it will just be the beginnings of the above ground plant, but not always in the best place compared to the top of the bulb. It is usually easy to break it, so be careful. I find it works well to make sure at least some of the growth is positioned to be above the soil. Otherwise it could get stressed trying to find light.
Once the bulbs are in the pot, all you need is a warm place where you can water them when they need it. You don’t want them kept soggy, but you don’t want them to get bone dry either. Once new green growth starts to show, I put them out on the patio every day. If you do this right away, they don’t have to transition from artificial light. It is a bit of a workout to carry 15 gallon pots in and out every day, but it doesn’t take that long and it is good exercise!
You may want to choose a location outside that is protected from rain and roof run-off, at least on days your are gone from the house or if it is going to rain a lot. A south facing exposure tends to be quite a bit warmer, especially right by the house. The dahlias will grow faster if kept warmer.
Using this method, and planting them in the pots during the first part of April, I have good sized, vigorous plants by the beginning of June. The roots have grown, creating a network for easy handling of the plant. When you are removing it from it’s pot, to put it in the ground, don’t forget to stimulate the roots to grow outside the pot space they have been used to. Some rubbing on the outside of the rootball should do be all it needs. Check your particular varieties for space needed per plant, both width and height.
The dahlias bloom all summer long, once they get started. They like open sun and warmth, but need to be regularly watered. I have never had the plants fade in the brutal heat of summer like many plants do; and dahlia make good cut flowers. If you can manage it, you could dig up the bulbs in the fall, after the foliage has died from a hard frost, but before the ground has frozen. If you have a cold pantry or root cellar, that would be a good place to store them, but they will want to be kept slightly moist, kind of like any root crop.
Next time you see a bag of dahlia bulbs while you are grocery shopping, remember they are low calorie. Actually, caring for them burns calories. Hey, you might even need to eat extra cookies just to keep up your strength!