WHEN TO PLANT
The best time to plant your tubers is after your last frost date has passed. And though a tuber underground will not be affected by the occasional late spring frost, soil temperature will. If you check THIS website, you can find trending soil temps in your area. Wait until your soil temps are consistently around 60 degrees. Dahlias need warmth to grow, and planting them into cold, moist soil often leads to rotten tubers.
If you receive your tubers and you still have a few weeks before you can plant them, check out our advice on WELCOMING YOUR DAHLIA TUBERS.
SOIL
Dahlias like loose, fertile soil, around 60ºF and not bone dry but not at all soggy. Set yourself up for success by doing a soils test - this will help you understand what your particular soil needs. I use UW-Madison's Soils Lab. If you are unable to get a soils test, mixing a bit of compost into your soil is a great way to add nutrients and improve drainage. I also throw a bit of starter fertilizer with mycorrhizae into my planting holes.
SUNSHINE
Dahlias require full sun, meaning ~8 hours of direct sunlight. More sunlight makes for stronger and sturdier plants with more blooms.
There are a few varieties that *don't* enjoy full sun in the heat of summer. We've made notes for those varieties - they are best planted with some shade cloth, or in a spot that gets a little shade in the hot afternoon.
WATER
This is important - do not water your dahlia tubers at planting time unless your soil is very, very dry. Tubers contain all of the moisture they need to start growing, and will rot if they are over-watered before they begin growing in earnest. Be patient, and wait to water them until you see green growth above the soil. It can be a few days, or a few weeks. Each variety grows at a different rate.
PLANTING & STAKING
This is also important - plant your dahlia tubers horizontally, not vertically, ~5" deep and at least 18" apart. I recommend adding a 4' stake at planting time, 8" deep and 6" from your tuber crown. Happy dahlias get tall and heavy with blooms, and staking them keeps them growing straight and strong. Staking them early eliminates the risk of stabbing your growing tubers later beneath the soil! If you are growing a lot of dahlias, there are more efficient ways to support them, but staking works very well for under 20 plants. :)
LABELING
If you want to keep track of what you are growing (And you really should, especially if you ever plan to share or trade tubers!) you should label your tubers 3 times per season: when you plant them, after they've bloomed, and when you dig them up.
When you plant them: My first label markers go in the moment after I lay a tuber in its planting hole, and I place them 12" in front of the tuber crown, or in front of the stake. I use a plastic or metal stake labeled with a garden marker. Don't use a sharpie - it will fade in the sun almost immediately. Don't use wooden stakes - they rot quickly in the garden.
After they've bloomed: I always do a follow-up ID to confirm the bloom is what I thought it would be. I like to label a bit of flagging tape and tie it around the base of my plant so when it comes time to dig, I know what I've got.
When you dig them up: Make sure your labeled flagging tape is connected tightly to the stalk that is connected to your tuber clump- if there's any risk of it falling off, I also tie a label through the clump, or write directly on a tuber with a sharpie. Digging/dividing is the biggest danger zone for tuber identity issues!
Happy growing! For a full list of the supplies we know and love, see our RESOURCES, TOOLS AND SUPPLIES list