Roll up your sleeves, it’s time to plant dahlia tubers! It can be a bit of work if you are planting many, but not so bad for just a few, and always worth it in the end. Planting dahlia tubers the right way will ensure a field or garden full of fabulous dahlia blooms. Learn how to plant dahlia tubers, to get your gorgeous dahlias off to a great start.
When To Plant Dahlia Tubers~ What Month
The date to plant dahlia tubers will depend on the growing zone that they are to be planted. It’s very important to plant after the risk of all frost has passed, since dahlias are tender plants, and will not fare well with frost. Consider your growing zone and plant after your last frost date.
Different planting zones will have different frost dates. Check out your frost dates here.
Keep in mind these dates are only estimates, and it is always a possibility that a late frost will occur, especially in the colder growing zones.
A good rule of thumb is to plant your dahlia tubers when the lilacs are blooming. Our lilacs are just opening up this week, so into the ground went our dahlia tubers!
I try not to delay the planting time, as it is also important to have lots of growing time in the ground to get blooms before the first frosts of fall.
Here in zone 5b we plant our dahlia tubers in mid to late May, and then cross our fingers that we don’t get a late frost, which is always a possibility.
If a frost touches the growing tips it will blacken them, however it will generally not harm the tuber, and more stems will be produced. It’s almost like an early pinching of the stem.
Can You Divide Dahlia Tubers In Spring~ Before Planting?
You can divide tubers in the fall or the spring, whichever is your preference.
Many people like to wait until the spring, as the eyes are more prominent and you can see the tubers that are good for planting.
If you do divide in the spring, make sure that you allow at least twenty four hours for the tuber to callous over on the newly cut part before planting into the ground.
We generally divide our tubers in the fall, to complete this arduous task long before the busy spring.
Although the eyes are not always readily visible in the fall, it still makes it easier for us to store away the tubers when they have been divided. This is the reason for our decision to divide in the fall.
Starting Dahlias In Pots
Some gardeners start their dahlia tubers early in the spring in pots, to give them a head start on the growing season.
This is especially helpful if you live in a colder growing zone, and you are waiting for the frost to pass.
These plants are then planted out into the garden when the frost has passed, and will have had extra growing time, and hopefully earlier flowering time.
To Plant The Dahlias Tubers In Pots:
- Choose one tuber per pot.
- Plant into a good growing medium, like a soilless potting soil.
- Plant approximately four to six inches deep.
- Keep the soil warm, and slightly damp.
- Dahlia tubers tend to rot fairly easily when they remain in a wet cool soil.
- Place the potted up tubers in a sunny location, such as a sunny windowsill or sunroom, or under grow lights.
- A greenhouse is ideal as well.
Once the weather has warmed up and the chance of all frost has passed, the dahlias will be ready to be planted into the garden. Make sure that they are hardened off prior to planting them out into the garden.
You can do this by gradually acclimatizing them to the outdoor elements by placing them in a protected area outside and then bringing them back in, slowly increasing the time over the course of a week or so.
Can You Plant Dahlia Tubers Straight In The Ground?
You can plant dahlia tubers straight into the ground, although it is important that the tubers are planted in an area that has fertile and well drained soil.
We plant most of our tubers directly into the ground.
How Do You Plant Dahlia Tubers?
We have heavy clay soil on our farm. We amended the soil with lots of organic compost the first year that they were planted in the ground, and amend every year with fresh compost at planting time.
The dahlias grew very well in the fertile amended soil.
Last year I had lots of extra tubers and planted some straight into the clay, with compost and bonemeal in the planting holes. These tubers grew, however not as well as those planted in the heavily amended soil.
The tubers planted in the clay did not grow as big, were more prone to insect damage, and some also produced flattened tubers at the end of the season.
Clay tends to compact when dry, and this would explain the shape of the tuber growth.
So lesson learned, all tubers this year have gone into wonderful soil, amended with lots of organic fish compost.
Do You Soak Dahlia Tubers Before Planting?
We do not soak our dahlia tubers before planting, although some do.
Even if the tubers are somewhat shrivelled and dry, if they have an eye and are starting to sprout, they will be planted as is.
Most of our tubers are sprouting by the time we get to plant them. The concern for soaking them would be that they would be more vulnerable to rot.
The tubers will rehydrate in the soil.
The Process for Planting The Tubers
There are many different ways to plant dahlia tubers.
You can plant the tubers directly into the ground, or into pots.
If planting into the ground you can grow them in rows, like we do at our flower farm, or plant them in a sunny spot in your garden.
We plant in rows that are four feet wide, with two rows of dahlias inside this four foot strip. We have a three to four foot walking pathway between the rows.
Some gardeners/ flower farmers who plant their dahlias in rows opt for one row of dahlias per row. This option is also a good one and allows for easy identification and organization of your dahlias.
We till our rows, due to our clay soil, and also due to the number of tubers that we have to plant.Tilling loosens up the soil and makes it more manageable to dig.
A no till approach however is optimal, if at all possible.
Tilling always brings weed seeds to the surface, and weeding will be a summer chore in the dahlia rows throughout the season.
Dahlias require at least six hours of sun per day for optimal growth. They will tolerate some shade as well, but do best in full sun.
We have planted both in full sun and partially sunny locations with good success.
We have had our best blooms however in full sun.
How Deep To Plant Dahlia Tubers
Make holes or drills at least 4 to 8 inches deep. Planting deeply will help to support the heavy plant as it grows taller throughout the summer.
If planted too shallowly they are at risk for tipping.
It’s always a good idea to add compost and bonemeal to the planting hole, as dahlias are heavy feeders.
Plant in the hole with the eye or the sprout facing upwards. Gently fill in the hole, making sure that the sprouted stem does not get crushed.
We bury the stems if they don’t reach the surface when planting. Otherwise, we will let them protrude if they are high enough.
We space our dahlias closer together than what’s normally recommended, as this is what we learned in the Floret workshop.
Normal recommendations for spacing is 1.5 to 2.5 feet apart, depending on the size of the dahlia variety.
We space out plants one foot apart, and this spacing has worked out well for us. The plants tend to support each other with the closer spacing, which is helpful.
The rows are then corralled along the outside edges of each row, on both sides for support.
Watering Your Dahlias After Planting
It is highly recommended that you do not water your dahlias until they are up through the soil and growing well.
The reason for this is the risk for the tubers to rot. Dahlia tubers can rot very easily.
Every year we have had a few casualties, and this just goes with dahlia growing.
So be careful with watering initially. After the dahlias are growing well, they will appreciate water every week.
Sometimes there will be enough water just from the rain, however if there is a dry spell the plants will need to be watered, up to an inch per week.
If you are planting just a few dahlias in the garden, you can add a support stake to your planting hole at the time of planting.
A strong bamboo stake works well for this purpose.
If planting dahlias in rows, corralling is another method to hold the dahlias up. You can also stake individual plants within the rows as needed.
Planting Dahlia Tubers In Pots
The first year we had dahlias, we planted them all in pots. It is definitely doable.
Those dahlias grew and flowered, and produced more tubers at the end of the season.
The reason we grew in pots was that our garden was not ready to be planted, and the ground was much too hard for dahlias. We grew about seventy five plants in pots.
If I was to do it again, the main thing that I would do differently is to make sure that the pots were heavy and weighted, so they are less at risk to being blown over by the wind.
We discovered that as dahlias grew they tended to get top heavy. Besides requiring supports in the pots, they also benefited from supports to keep the pots upright, especially if the soil in the pots was somewhat dry and light.
To protect some of the taller heavier plants that season, the plants were staked inside the pot, but also tied to a trellis to keep the pot and plant from blowing over in the wind.
Recommendations if growing in pots:
- Use a heavy pot with good drainage, and a solid base that will not blow over in the wind
- Shelter from the wind
- Use good fertile soil or potting mix
- Water regularly as they may dry out more quickly in pots~ but do not over water as you will lose some plants to rot.
When Do Dahlias Bloom?
Dahlias bloom about two and a half to three months after they are planted. Some of the larger varieties will need a little more time.
We usually start to get a few blooms by mid August, and by September the dahlia garden is in full bloom.
Can You Leave Dahlias In The Ground Over Winter~ To Avoid Spring Planting?
Dahlias can be left in the ground in warmer zones to over winter.
In our zone 5b garden the ground freezes hard and deep, and dahlia tubers would not survive the winter.
Generally, if you are in a zone where your ground does not freeze, the dahlia tubers would likely fare well with overwintering.
It is very important that there is good drainage in the soil, and that the tubers are not left in cold wet soil over the winter months.
Love ‘N Fresh Flowers are in zone 6B/7, and have successfully overwintered tubers, albeit with lots of protective covering. Read Jenny Love’s post here.
In our zone 5b garden we are not able to leave dahlias in the ground over winter. Our dahlia tubers are lifted and divided every fall, and safely stored away for the winter. It is a difficult task, but a necessary one.
Have you planted dahlia tubers in spring? Be sure to leave a comment below to share your thoughts!
There are lots of ways to plant the tubers. Wishing you the best of success with your dahlia tuber planting!