Growing Dahlias

GROWING DAHLIAS

Growing Instructions and Tips to help you succeed in growing Dahlias!

Tubers:

1) Tubers come in all shapes and sizes - rest assured, the size and beauty of the tuber does not matter!! You can still get beautiful flowers from even the ugliest and tiniest of tubers as long as it has a viable eye. Tubers have three parts (see photo below): Crown (top where the eye/shoots come from), Neck (the narrow part that connects the crown to the tuber body - sometimes the neck is skinny and long, other times it is short and fat barely visible), and the Body (this is the fatter part where the nutrients are stored for the plant) where the roots will grow from. 

2) When you receive your tubers, they will have at least one viable “eye” - this is where the sprouts with leaves will grow from. Some tubers may already be sprouting when you receive them. If a tuber doesn’t have anything growing from it's eye yet when you receive it, keep it warm and the sprout will grow. Some are just more eager while others are sleepy. If a sprout gets broken or knocked off, don’t worry - it will grow even more back to replace it! Sprouts can be green, burgundy, or white - they will all turn green eventually.

3) Once you receive your tubers, it is recommended you do either of the following: 

   - Pot your tubers up immediately to give them a head start on growing. Some growers add soil to a baggie and put the tubers in those to start them. If you choose to pot them up, I would recommend keeping them in either a very bright window or under growing lights once the sprouts break through the dirt and leaves start to form, or they can get weak stems without enough light. When potting them up, use whatever pot will fully cover the crown of the tuber. I have potted tubers vertically or horizontally and haven't found much difference in their growth habit. 

   - Store them somewhere cool (between 5-15°C) and dark until you are ready to plant them directly outside after the last chance of frost has passed. You can store them in a covered container in a medium of your choice (ie. soil, vermiculite, wood shavings), leaving the lid cracked slightly. If they seem too dry, you can very lightly mist them. If you choose to store them until they are ready to go outside, check them consistently to make sure they are not too moist or too dry. I prefer to keep mine fairly dry as you can always bump up the moisture, but can't stop them from rotting once it sets in due to too much moisture.

I prefer to pot my tubers in advance of planting outside as I find they have a better chance of surviving a wet spring season if they go into the ground with roots and leaves already established. Too much moisture for a tuber without roots is almost a guarantee that it will rot. 

Potting a Tuber:

1) If you choose to pot up your tuber before planting, I would recommend a good quality potting soil that has good drainage, like ProMix HP Mycorrhizae (you can find this one at Canadian Tire). You can also add coarse perlite to most regular seed starting mixes to increase the soil porosity and ensure it has adequate drainage. 

2) Lightly dampen the soil so it is barely moist (remember too wet = ROT!). 

3) Plant the tuber vertically or horizontally in the pot. You can either leave just the top of the tuber crown visible (where the shoots will come from), or bury it under the surface and wait for sprouts to break through the top.

4) Leave the pot somewhere warm (20°C is good) until you see sprouts come up.

5) Once you have sprouts, I like to keep the soil a bit more moist. Some tubers will arrive to you already with a sprout, and possibly some roots as well. They will start to need more water once they have roots and shoots. 

6) Give them lots of light once they sprout as well, or they will start reaching too high looking for light and the stems get skinny and weak. 

 

Planting Tubers Outside:

1) Dahlias are not cold tolerant and should only be planted outside once all chance of frost has passed (usually around the May long weekend in southern Ontario). Frost can kill them. Optimally, keep an eye on the weather and plant outside once overnight temperatures are consistently over 10°C. 

2) Dahlias prefer being in Full Sun, but can handle some shade.

3) Spacing for dahlias is best between 12-18” apart - some varieties can get quite large and if they are planted too closely, they will crowd each other and none will grow the best they can.

4) Plant your tuber crowns at least 4-6” below the soil surface. If you started tubers indoors in pots, remove the lowest leaves if needed to plant it deeper.

5) If you have heavy clay soil, I would recommend adding manure, compost, perlite, or triple mix to help amend and ensure the soil doesn’t stay too wet.

6) Don’t overwater the tubers after planting. They need very little moisture until they’re established with roots and shoots.

7) You can plant them in the ground, raised beds, or larger pots (I would recommend at least a 5-7 gallon pot size per tuber). 

8) Depending on your soil health, I like to add a bit of fertilizer to the planting hole when I plant the tubers. I use worm castings and that seems to keep them happy. 

9) Once your plant has at least two or three sets of leaves, it is recommended to also pinch your main stem - this means cut the main stem just above the second set of leaves. It will signal to the plant to send out two side shoots to replace and will give you more blooms. There are many "dahlia pinching" youtube videos on this if you need further guidance.

10) I also recommend staking dahlias with a rigid post/stake and twine once they get bigger otherwise they may flop over or break when it is windy.

11) Removing the lower sets of leaves once plants are established (ie. over 1ft tall) can also help with air flow and reducing powdery mildew. 

12) Earwigs, aphids, and Japanese Beetles are some of the ravenous pests that will eat your blooms before you can enjoy them. If you are looking to cut some of your dahlias for a bouquet, I recommend finding some mesh organza bags to put over the flower heads before they bloom to protect from hungry pests munching your petals. Dahlias are sensitive to herbicides as well - if you or your neighbors use herbicides, it may harm the growth of your dahlias. 

13) If you want to keep your tubers to grown again next year, you will have to dig them up in the fall after frost kills the plants, and then divide and store them over winter indoors. Please google ways to store dahlia tubers - there are many ways you can do it and everyone does it a bit differently. I had excellent success storing them in vermiculite in my cold cellar with a digital thermometer to keep an eye on the temp and humidity. The Hamilton Dahlia Society and the many dahlia facebook groups also have good community resources for growing, dividing, and storing dahlias.

Feel free to message me at hello@agreenerplace.ca if you need any further guidance or if you have any other questions!