What Dahlias Need in October: 6 Easy Tasks for Plenty More Blooms and Winter-Ready Tubers

Early October is peak flowering time for most dahlias, and the right care now will influence not just how many more blooms you enjoy into fall, but the health of their tubers you’ll soon be digging up to store over winter. Dahlias thrive during this season’s warm days and cool nights, and will reward you with spectacular and abundant blooms. But if you want to enjoy the same dazzling show next year, you need to strike a balance between pushing for more flowers and prepping those tubers for storage. So, if you're wondering what dahlias need in October, balanced care is critical.

Fall dahlia care also depends heavily on your growing region and climate but for most gardeners, early October should bring a focus on cleaning up plants, preventing new green growth, supporting tall stems, and monitoring and managing pests and diseases. Get it right and you’ll get plenty more blooms as well as plump tubers full of energy that’ll overwinter well, ready for a repeat performance next year.

Ready? Let’s dive into what to do with dahlias in October.

1. Keep Watering, But Don’t Overdo It

Part of the fall balance for dahlias is irrigation levels. While plants are still putting out impressive blooms, they’ll be using plenty of water, but their tubers are also preparing to toughen up for winter – and too much moisture means those roots get soft and won't store well. Add rainfall into the mix and there’s even more to consider, especially if you're growing dahlias in containers.

The best guideline is to water your dahlias if it doesn’t rain, once the soil has dried out. But then water deeply. A rain gauge such as this pretty precipitation gauge stake from Amazon is a really simple but effective way to keep an eye on how much rainfall your plants are getting, so you can water accordingly. Irrigate at soil level, never over the plants, and try to avoid getting foliage and stems too wet.

As October proceeds, gradually cut back on how much water you provide so the tubers start to toughen their skins.

2. Deadhead Flowers

As long as you keep removing spent blooms, you’ll direct the plant’s energy into growing more blooms rather than seed production. To deadhead dahlias, cut the faded flower stem back to the next branching point. Of course, you don’t need to wait for the petals to fade before cutting, as now you can be enjoying cut flowers as your reward for all your hard work. Snipping freshly opened blooms will also encourage plants to continue producing more.

With some dahlia varieties, the spent flowers look very similar to new buds. If you're not sure which is which, give it a gentle squeeze: fresh about-to-open buds will feel firm to the touch while spent blooms will feel a little mushy.

Of course, if you plant to collect seeds, leave some of the flowers in place.

3. Support Stems if Needed

All these heavy blooms can start to weigh down the stems, especially if you're growing dinnerplate dahlias, and it’s common to see plants splay at this time of the year. If you don’t already have them in place, add stakes to help top-heavy stems stay upright. Not only do vertical stems look better, broken stems can create wounds that are vulnerable to disease.

Bamboo canes will do the job just fine, but make sure you buy poles that are long enough, like these reusable 5' support stakes from Walmart, as you’ll need to push a quarter of the length into the ground. Tie individual stems into the stakes using soft twist ties such as these from Amazon that won’t cut into the plant material, or simply fashion a cradle around the whole plant with canes and twine.

If you do have supports in place, check them and make adjustments as needed, especially after heavy rain or windy weather.

4. Watch Out for Pests and Disease

As part of regular maintenance, you should be looking out for signs of pest infestations or diseases taking root in your dahlias. Do this throughout the growing season, but especially now, as you want your plants to stay healthy as they build up energy and tough, healthy tubers for winter storage.

Some of the typical pests you’re looking for in October include spider mites and aphids, both of which feed on dahlias. Pests are less of a concern this time of year as growth is wrapping up anyway, but it’s still worth removing them with a spray of water or use an organic neem oil spray such as Bonide Captain Jack’s Neem Oil, available from Lowe’s, to keep your plants looking tidy for the rest of the season.

Increasing rain and lower temperatures in fall can increase the prevalence of powdery mildew and leaf spot. While there’s no need to worry, if you spot a white dust-like coating to leaves, it’s best to remove them to reduce the amount of infected plant matter in your garden beds. A collapsible waste bag like Fiskars 10-Gallon Yard Waste Bag, available from Amazon, makes it easy to transport them straight to the trash, as you don’t want these fungal spores in your compost bin.

5. Gradually Stop Fertilizing

Feeding dahlias as we head deeper into fall pushes the plant to make new growth rather than harden off its tubers ready for storage. Particularly, avoid the temptation to use up any high-nitrogen fertilizer which promotes leafy growth. If you're gardening in a warmer zone and still feeding to promote flowering, make sure the fertilizer is designed specifically for that job. Look for a low- or zero-nitrogen feed such as TPS Flower Fertilizer, available from Amazon, that’s rated 0-10-10 or 5-10-10 – the first number indicates nitrogen levels, so this must be lower than the second two numbers that indicate potassium and phosphorus.

Aim to stop fertilizing completely 4-6 weeks before your first expected frost date, to give your plant time to mature its tubers.

6. Prepare for the First Hard Frost

If You Garden in a Cold Zone

In zones 7 and below, you’ll need to dig up and store your dahlia tubers over the winter. Depending on the zone you garden in, your first frost could hit in October, so make sure you’ve got everything ready. Coco coir such as this from Walmart in a cardboard box makes for cheap and effective storage.

Always wait until the first good frost has killed the stems above the ground, as this triggers the plant to send a rush of sugars and starches down into the tubers. Not only does this mean lots of energy stored for next year, it tells the plant to enter dormancy and mature the tubers, when they’ll store better.

It’s best to leave tubers in the ground to rest for 1-2 weeks after this frost to allow this process, unless you suspect the soil will freeze, when tubers will die, or rainfall is heavy and incessant, when roots may start to rot.

If You Garden in a Warm Zone

If you live in the warmer climates of zones 8-11, you can safely leave dahlia tubers in the ground as long as you have well-draining soil. If you have a frost, wait a week or two to allow the energy transfer into the tubers then cut stems down to around 3-4 inches and pile a 5-inch layer of mulch such as Back to the Roots Organic Mulch, available from The Home Depot, over the soil to act as a cozy duvet.

In frost-free zones, cut stems by mid-December at the latest to ensure plants rest, and there’s no need to mulch.

As you look ahead, adjust your plans to the weather as temperatures and rainfall can vary widely in fall. Keep enjoying those spectacular October blooms but remember you need to start caring for the tubers, too, if you want next summer's display to be equally stunning.

Stock Up On Showstopper Varieties

October is a great month to buy dahlia tubers as you'll be able to find more unusual varieties and dahlia types that are usually snapped up months before the first hint of spring. Most specialist dahlia retailers open for pre-orders in October then send tubers out in spring, though it's fine to physically buy tubers now as you can safely store them for spring planting.
Take a look at Dutch Grown's impressive dahlia collection of over 150 cultivars for inspiration, and here are just a few varieties new for 2027 to give you a taste of the incredible flower shapes and color combos now available.