You Bought Dahlia Tubers…Now What?
So you Bought Dahlia Tubers….Now What?
Dahlia tubers get planted in the late spring and bloom starting about the end of July for several months until the first frost- early November here in Western Oregon.
I always plan to plant around Mother’s Day- mid May, but if you are in a different zone than I am (8b), then you need to know your last frost date.
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It is safe to plant your tubers around that time. Remember, that the tuber has some protection from frost when it is planted in the soil, compared to if it is growing a green shoot.
Prepping your planting area:
Clear of all weeds.
Choose an area that doesn’t have standing water- you want good drainage.
Pick an area that has at least 6-8 hrs of full sun. If there is too much shade, you will get long, stringy plants with very little blooms.
Either rototill to loosen your soil, or take a shovel and loosen each spot you will plant your tuber. This will allow its roots to grow more easily.
Planting:
Plant at least 12” apart side by side. If you are planting 2 rows alongside each other, I would at least allow 2’ between rows. For the walking paths, I have learned to give 3 feet so I have plenty of room. If you aren’t planting in a row to conserve space, feel free to give your plants 18” or more between plants.
When planting a tuber, dig a hole 5-6” deep. You will lay the tuber horizontal on its side. You want the eye (the growing point), below the soil at least 5”. This will help it make more tubers and will give the plant more stability. Cover up with soil and the most important part, place a label right away with the name of the tuber.
DO NOT WATER at this time. It could cause your tuber to rot. Don’t worry if it rains, but only add water later on if your soil is BONE dry. Otherwise wait to water until you see some green growth popping through.
This is a good time to place plant supports. You can use a tomato cage over each tuber, or if you are planting a whole row, you can use wooden or metal stakes. I place my stakes about 10’ apart.
Now expect about a month until any green growth pops through the soil. During this time, check occasionally that slugs aren’t eating any new growth.
If so, I like to use Sluggo granules. It kills slugs but won’t hurt your pets. You only need 1-2 granules per plant, so sprinkle lightly.
Some dahlias take longer to emerge than others, so be patient. If you are concerned, carefully pull away soil to peek at the tuber. Sometimes if mine doesn’t sprout, it is because they have rotted. Another reason is if the tuber has no eye. If it does not have an eye, you do not have a viable tuber.
Fertilizer:
You can use fertilizer 30 days after planting. You don’t want to use a high nitrogen fertilizer.
A 5-10-10 or something similar to that is great. While plants need nitrogen, they don’t want high nitrogen. The plant will have beautiful green growth, but not many blooms. (The first number in 5-10-10 is the nitrogen number.).
I would recommend 1x per month until you reach the first of September. Stop fertilizing after that unless you use a 0-10-10. (Since this fertilizer does not have nitrogen).
Fertilizing too late can cause your tubers to not store well.
Pinching:
When your dahlias grow to 12” tall, this is when you want to pinch. Find a set up leaves around the 12” height and pop off the growing point above the leaves. This will allow your plant to produce many more blooms and grow a much fuller, bushier plant.
Watering:
Dahlias love water once they are up and growing. They like deep watering, so I would recommend at least watering 2-3x per week for an hour. If really hot, you will need to do more.
I would highly recommend you set up some drip irrigation or an overhead sprinkler on a timer to make it easy.
Staking:
If you have your dahlias planted in a row, I start putting up string on my stakes after I have pinched the dahlias. Your plants will grow tall and you want to prevent them from flopping over in the wind and rain.
Harvesting:
Dahlias need to be ¾ or more of the way open before you harvest. They will not open if cut when they are a bud. Cutting deep (18”-24” down) will give you long, sturdy stems when the next bloom pushes up. The more you harvest your dahlias, the more blooms you will get. They are not stingy plants!
Frost:
In my zone, plants start to slow down toward the middle/end of October. You will notice more of your dahlias have blown centers. This is signally that their best growing time is done. If your tubers have been in the ground at least 120 days, then you are safe to dig up your tubers.
Some growers like to wait until the frost has come to kill the foliage and then dig up. Others will cut down the foliage, then wait 1-2 weeks to dig because it can be easier to see the eyes of the tubers when dividing.
If your growing zone is lower than 8, then I would recommend you dig up your tubers. Otherwise they may freeze or rot. You can also try covering with plastic or leaves and see if you get lucky. If you have really cold winters, you will definitely need to dig your tubers.
I hope you learned a lot and I hope you have a great dahlia growing season. If you have some hiccups, don’t worry, like all farmers say, “There’s always next year!” Every year you will learn something new to carry forward for the next year.