I used to think my late-summer garden had to look tired. That was before I figured out that August is the make-or-break month for dahlias. This list has my personal routine to keep them loaded with flowers until the first hard freeze, all tested, all practical, and all worth the extra ten minutes a day.
Quick Summary
- 7 essential late-summer maintenance steps for dahlias.
- Keeps plants flowering heavy through the autumn cooling.
- Best starter task: Consistent deadheading — the single most important habit.
1. Deadheading Spent Flowers
I find deadheading is the absolute foundation of getting more flowers. If you don’t remove the old blooms, the plant stops making buds and starts producing seeds.
It’s similar to how we manage other perennials that bloom multiple times a year to keep the garden colorful.
I make a game of checking my patch every single evening. The trick is knowing what to snip.
Spent flowers look soft and pointed, while unopened new buds are round and hard. Trust me, they look similar at first glance until you touch them.
Don’t just pull the flower head off. I always cut the stem all the way back to the next set of leaves.
This tells the plant to send out fresh side branches.
Tip: Keep a clean pair of shears in your pocket so you can do this as you walk the garden.
2. Pinching Out Side Buds (Disbudding)
I want my dinnerplate varieties to look like showstoppers, not crowded clusters. To do this, I use a trick called disbudding.
Look at the very top of a stem and you’ll find three buds clustered together. I gently pinch off the two smaller side buds, leaving only the large central one.
This directs all the energy into one massive flower instead of three small, weaker ones. It feels wasteful at first, but the results are worth it.
I only do this for the giant dinnerplate varieties like Cafe au Lait. For the small pompon types, I let them all grow.
Tip: Do this early in the morning when the stems are crisp and snap off cleanly.
3. Shielding Buds with Organza Bags
I used to lose half my blooms to insects before they even opened. Then I started using cheap organza jewelry bags.
When a bud starts showing a sliver of color, I slip a bag over it and pull the drawstring mesh barrier tight.
The mesh keeps the bugs out but lets light and rain in. Seriously, they look a bit silly on the plants, but they work.
I leave the bag on until the petals are ready to unfold. It’s my favorite secret weapon for perfect flowers.
Tip: Use the four-by-six inch bags for standard sizes and six-by-eight for dinnerplates.
4. Targeting Earwigs with Spinosad
August is when earwigs reach their peak, and they love eating dahlia petals. Honestly, standard slug bait is useless here because it only targets slugs.
I use a bait containing spinosad, which specifically controls earwigs. I sprinkle it around the base of the stems where they hide during the day.
Targeting this area is critical for earwig control before they reach the buds. According to the University of New Hampshire Extension, spinosad is a reliable choice for managing chewing pests in home gardens.
It keeps them from climbing up the stalks at night.
Warning: Apply the bait in the evening so you don’t disrupt active bees.
The garden tasks that take the least time often save the most flowers.
5. Switching to a Low-Nitrogen Feed
I stop using high-nitrogen fertilizer by the time August hits. Too much nitrogen now makes the plants put out soft, leafy growth that breaks easily.
I switch to a fertilizer high in phosphorus and potassium instead. A simple five-ten-ten mix works well for my beds.
This helps the roots stay strong and encourages bud formation instead of green leaves. It’s a similar balance to how to fertilize zinnias for the best late-season color.
I stop feeding them entirely by the end of the month. This allows the tubers to ripen and prepare for winter dormancy.
Tip: Always water the soil before feeding to avoid burning the roots.
6. Watering Deeply at the Base
August heat dries out the soil fast, but shallow watering does more harm than good. It’s a lesson I also learned when figuring out how to keep clematis blooming all season in dry weather.
I soak the ground deeply two or three times a week rather than spraying daily. I direct the water right at the soil level using a soaker hose.
Keep the leaves dry. Spraying the foliage in late summer is a fast track to powdery mildew problems.
I’ve lost entire beds to mildew because I got lazy with the sprinkler. Now I stick to the ground level.
7. Reinforcing Stakes and Support Ties
A heavy late-summer rain can snap a thick dahlia stem in seconds. I learned this the hard way during my first season.
As the plants grow taller and the flowers get heavier, they need extra support. I drive sturdy stakes deep into the ground next to the main stems and tie the branches loosely with soft garden twine.
We need to secure them before the heavy autumn storms roll in. I also run a perimeter line of twine around the outer branches.
This keeps the whole plant from splaying outward when the wind picks up.
Tip: Check the ties weekly to make sure they aren’t cutting into the expanding stems.
The Three Tasks I Never Skip
If you only have ten minutes a day, focus on deadheading, checking the stakes, and bagging the best buds. Those three simple steps make the biggest difference in my garden.
The rest can wait, but the flowers won’t.
Common Questions
1. Why are my dahlias growing tall but not blooming?
This is usually due to too much nitrogen in the soil. Switch to a fertilizer high in phosphorus and potassium to encourage flower buds.
2. How do I know if a dahlia bud is spent or new?
Spent blooms are soft, squishy, and have a pointed tip. Unopened buds are firm, rounded, and feel like solid marbles when you squeeze them.
3. Should I cut dahlias for bouquets to get more flowers?
Yes. Cutting the flowers for bouquets acts just like deadheading. It stops seed production and prompts the plant to grow more blooms.
— Anh