If you are taking the leap of faith and planting dahlias, YAY, Congrats! You are going to have so much fun. Dahlias are my favorite summer cut flower!
Here's why:
They bloom for an incredibly long time (June-October)
The more you cut the more they produce ( this is what we call a “cut and come again” flower)
Lastly they will continue to bloom year after year for you. In the winter time when the frost hits let the plant die back naturally, it might look brown and crusty for a while. Then take your clippers and cut the plant back to the ground. Stop watering it after it frosts, this will prevent your tuber from rotting and not coming back the following year. Start watering it again in March when it starts to push green growth again.
Dahlias are grown from tubers. They honestly look like little sweet potatoes. They come in all shapes and sizes but you only need three parts of the tuber for it to turn into a viable plant. The three parts are the crown, the neck and the body. Check out the photo below for reference. Dahlias can be grown from seed but this is not the most common way you will find them.
Step by Step Instructions:
Dahlias require at least 8 hours of sun to thrive. With our extreme temperature in the Central Valley afternoon shade is a great option is possible. We have grown dahlias in full sun for the past three years with much success, only this year we are in the process of installing a 30% shade cloth for our field. They thrive in the heat but just like anyone in the 100+ heat you feel overheated and droopy. But just give them an extra shot of water in the sunny summer days and they will be totally fine.
Dahlias need to be planted into well draining soil. Its best to amend your soil with high quality compost compost before you plant. You can find these soil amendments as your local nursery.
Dig a 4-6 inch hole and place the tuber (eye up) on its side. If you have multiple to plant make sure you give them plenty of room to grow, they need about 12-18 inches between each plant. They get really bushy and tall.
Cover your dahlia with dirt and water it in. Do not water it again until you see the green growth popping up through the surface. If you overwater in the early stages of its growth the tuber may rot.
Dahlias LOVE and NEED water. Giving them consistent water will be the key to strong, green, abundant dahlia plants. Hand watering is not enough, you will need to install a soaker hose or drip irrigation for best results. We water ours on an as needed basis, if the soil is dry we will water, you don't want it constantly soaked but you do not want it to be bone dry as well. If you need help with this, I suggest buying a soil moisture meter- here is a link to one Soil Moisture Meter Link. Inconsistent water can lead to less productive plants, yellowing and droopy plant leaves.
When it reaches over 100 degrees the plants can’t take up enough water through its roots to prevent it from wilting. To help prevent this, you can literally hose it down- like you would with your dog or kids when it's hot outside and you set up a sprinkler. This helps cool down the dahlia plant when it's too hard for it to cool itself.
Once your dahlia plant reaches 8-12 inches long you are going to need to pinch it. This promotes low branching growth to give your dahlia flowers a strong foundation. This increases stem length as well as the amount of flowers per plant. Basically you are telling the plant to divide its energy up and not just focus on giving all its energy to the central shoot.
You are going to need a clean, sharp pair of clippers, you are going to go 3-4 inches down the plant in between a set of leaves and above the new growth and clip it off. See picture below for reference
As your plant continues to grow and thrive you will need to protect them with some sort of corraling method, stake etc. to prevent them from falling over. If you have a lot of dahlias and you are able to put t-posts around the four corners of the dahlia plants and use rope/bailing twine to wrap around the dahlias. (See diagram for reference) If you have them spread out or only have a few, placing a stake in the ground and tying the plant to the stake is probably a better option. Placing the stake is best done when planting the tuber or plant- this way you do not strike the tubers when it's in the ground.
When it's time to harvest you want to make sure it's done at the proper stage. Dahlias only open a little bit more after cutting. If you look at the back of the flower head you can tell how old it is, you want to pick it almost fully open and the petals should be firm. If the petals are limp and shively that is when you know it is too old.
Bloom Promotion- if you leave your flowers on the dahlia plant for too long, your plant will start to think it needs to start going dormant. Continuously harvesting the flowers, even the ones that are too far past its proper harvesting stage. Remember the more you cut the flower the more they will produce so check your plants regularly and cut any flowers that are ready.
When the frost comes let your dahlia plant die back naturally, it will probably look brown and crusty but after a while you can cut back the dead plant to the ground. Stop watering it at this point, start watering it consistently again when you see new growth the next February/March.