Plant Dahlias Now for Late Summer Color

Still chilly outside and you are starved for color? Plant dahlias for late season color. It is like money in the bank. You are glad you did it early on as you know good things will happen later. Gardening in all about anticipation!

Lined out dahlias at Arundel Castle in the UK, picture by Amy Sparwasser

Ordering Dahlia tubers

Order your dahlias now. I recommend Longfield Gardens for all my dahlias as I have always gotten large plump tubers that are ready to jump!

Dahlia tubers come packaged in peat moss to keep them moist

When you first receive tubers you’ll want to do one of two things – plant them, or store them until you are ready to plant. The best way to store tubers prior to planting is in a cool, dry, dark place. Packed in some kind of material like peat moss and/or pine shavings, your tubers will be fine for several weeks in that material and some will even sprout.

Be sure to label your plants so you know the varieties that perform well

Dahlia tubers can be potted up and planted early in the season, but the plants should not be planted outside until the planting area is frost free or the soil temperature reaches at least 60 degrees. If you plant them and then get surprised by an upcoming frost, cover your plants to protect them with row covers, sheets or whatever gets the job done.

I inserted my cooking thermometer into the soil and it read 50 degrees- not quite warm enough

This year I tried to plant dahlia tubers in pots in my greenhouse to get an early start. This one came up and I pinched it back to make it stronger and bushier

Some people say plant dahlia tubers when you plant your tomatoes, but I have already planted my tomatoes and the soil is still only 52-53 degrees. Maybe another week will do it!

Planting

Heavy feeders, dahlia tubers should be planted in loose fertile soil. Add compost or bone meal to the soil before planting. Don’t plant in soggy soil; they need good drainage to be successful. Tubers can rot if planted in wet cold soil in the spring.

‘Campos Gibby’ dahlia seen at Longwood Gardens

Pick a sunny spot as dahlias love sun. If you have some shade, your dahlias won’t flower as much and the plants not as full and bushy.

‘Emory Paul’ is a gorgeous pink dahlia

Planting

Plant tubers by digging a hole three to six inches deep and laying the tuber in it with the growing tip up. The growing tip or bud is obvious as a fresh emerging shoot coming out of the fleshy brown tuber or an old stem that was cut off. Cover with about an inch of soil but don’t water until well after growth emerges. Plant the tubers about 18 to 24 inches apart because they produce bush-like plants. If shoots have already formed, then pinch them back to 2-3 inches. They will come up stronger.

Planting a ‘Cafe au Lait’ dahlia tuber in the spring that has already sprouted; pinch back the white sprouts to 2-3 inches

‘York and Lancaster’, an heirloom dahlia from Old House Gardens

Care

Staking can be done with tomato cages or with stakes and twine and should be done when you plant to avoid damaging the tuber. Most dahlias need to be staked or you will have a plant with branches that will flop on the ground and have misshapen flowers. Water if you don’t get at least an inch of rain per week and the plants benefit from feeding lightly with a granular or liquid fertilizer of a general use fertilizer – not high in nitrogen. High nitrogen will produce more foliage than flowers. I generally look for a fertilizer that is recommended as a bloom booster. Dahlias like cooler conditions, so flourish especially well in the late summer when temperatures start to moderate.

Seen at Longwood Gardens, dahlias are lined out in rows and at the end of the row, stakes are hammered in and tied with twine

Saving/Storing

Frost will hit your plants sometime in October or November and they will go from glorious specimen plants to blackened wilted skeletons overnight. Check your weather report and before a hard frost is forecast, cut off every flower and bring it in to enjoy for another week.

Bring in your dahlias before a killing frost and enjoy

Once the plants are frost killed, you can start digging around the root ball carefully to remove the shrunken starfish-like tuber that is nestled a few inches under the soil. Wash off any soil with a hard stream from your hose and dry in the sun. If you leave you tubers in the ground, I have found that some even come back if the winter hasn’t been too cold. Some people don’t save them, preferring to buy new ones every year.

Use a digging fork to dig up your tubers

Wash off your tubers in a crate for easy cleanup

Wash off the soil and dry the large tubers in the sun

Cut the stems a few inches above the tubers and store them in a container full of peat moss and perlite. I only place two layers of the tubers in a container, as I find that the bottom layers tend to rot more often than the top. If the tubers are too wet, they might rot anyway, so I check them after a couple of weeks of storage to see how they are doing. If they are moldy, I scrape off the mold and add some dry peat moss. You are going to lose some of the tubers, but I have a success rate of about 75% saved tubers.

Storing tubers in peat moss

Using a large rubbermaid container that has a layer of peat moss and perlite

Alternative Method of Planting/Saving

Another method is to plant your tubers in 1 gallon plastic pots early in the spring. When the weather warms up, plant the whole pot in the garden and cover with soil. Leave the tuber in the pot and roots will come out the bottom drainage holes. When frost hits, dig up the entire pot, cutting off roots that are outside of the pot and bring the pot inside and place in a cool dark place for the winter. When shoots come up in the spring, top dress with compost and plant outside for another season of bloom. I read about this method on Old House Gardens and want to try it next season.

Dahlia ‘Gallery Art Deco’ from Longfield Gardens is a stunner

Another method which a friend swears by is to dig up the tubers and shake the loose soil off and place in a large trash bag, leaving all the clinging soil attached to the tubers. Store the trash bag in an unheated garage that won’t go below freezing. Easy and effective!