Seasonal Articles 2025
Suggestions for the Dahlia Garden in Fall
Before first frost: 1. Complete your dahlia record keeping!
Check if you received and grew the correct variety. Do flowers match the name tag? If unsure, Google pictures of the variety to confirm its identity. (Note: flower color & form might differ slightly in cooler temps as compared to summer.)
Take pictures of the blooms, possibly the entire plant.
Note key characteristics and comments that might be useful when planning your dahlia beds for next year. Either directly annotate photos on your phone (fast) or on a separate spreadsheet. Suggestions on what to record:
Height of plant & staking needs. Next year- plant short varieties in the front, provide tall varieties with stakes.
Bloom characteristics for shows: Does the average bloom match its classification (size, fully double, good color)? Or do blooms have flaws such as asymmetric shape, low petal counts, fading color, open centers in fully double varieties?
Bloom characteristics for cut flower gardens: Does the variety bloom all summer or only for a short time. Are there many flowers per plant, good stems, nice flower color and size suitable for arrangements?
Health of foliage, signs of viruses, or disease susceptibilities. Are plants prone to mildew or fungal diseases, insect pests such as stem borers, aphids or mites? Are there signs of virus on the foliage? Next year, plant mildew prone plants at the corners where they get more airflow.
Approximate time of peak bloom: early summer (July), mid-summer (August) or late summer/fall (September or later).
Finally, note if you want to grow this variety (and these tubers) again next year or replace it with something new.
Discard failures such as diseased plants and possibly those which never bloomed.
Weigh the effort of overwintering against the cost of buying new tubers if you only have a few plants or no space to store tubers over the winter.
Consider donating your extra, disease-free tuber clumps now for next year’s tuber sale.
Label all plants that you want to dig up. Attach a ribbon or tag with the variety name or general description (flower color and form) to the base of the stem and note if you want to keep or maybe donate them.
Before first frost: 2. Collect ripe or nearly ripe seed pods!
If interested in growing dahlias from seeds next year, try saving your own dahlia seed pods now. You can also share seeds with friends or donate seed.
Note: Seeds need to undergo a ripening process on the plant. Seeds ripen at different speeds inside the seedpod. It takes about 4-6 weeks from flower to seed.
Immature seed pods are soft and very green.
Mature seed pods feel dense, have a golden color, and very little green left on the outside. Seeds inside the pod are turning black or dark brown.
Very ripe seed pods are brown. Place ripe seed pods in a paper bag for storage; don’t store them in a plastic bag until they are completely dry to prevent mold. Label with the name of the seed parent.
Cut mature/yellow pods with stems and label each pod with the name of the seed parent. Slightly less mature pods can be left in a vase to mature inside.
Let pods mature in a cool and dry place until ready to store/clean seeds.
Video about seed saving from Floret Farms: https://www.youtube.com/watch?v=qxmZagHqEz4
After the first frost: Get ready and dig your tubers!
Wait to cut down plants until ready to dig or the hollow stalks might fill with rain water and rot down to the tubers.
When digging your tubers - consider prioritizing favorites and expensive varieties just in case bad weather delays the rest of your dig.
Sometimes it’s easier to lift tuber clumps if you leave longer plant stems.
Before digging, consider how big the tuber clump might be. For large varieties, carefully dig in a circle of at least 12” diameter around the old dahlia stem. This should sever some of the thin feeder roots and make it easier to lift the clump without breaking the tubers’ necks.
Lift the clump out of the soil with a spade or digging fork.
Attach a label with the variety’s name to the clump.
Clean most of the soil off the tuber clumps, then cut down stems as far as possible (stems will rot), and remove any soft or rotted tubers. If the weather allows, you can also wash clumps to make them easier to divide later.
Let clumps dry at a frost-free place until ready to store or divide.
Don’t over-dry clumps! Tubers are dry and ready to be stored when they feel warm to the touch, and are no longer cold or clammy. If necessary, temporarily cover clumps with a plastic sheet (tarp, plastic table cloth) to prevent them from shriveling.
Don’t leave tubers sitting directly on concrete or in a cardboard box. This will dry them out too quickly.
Get your storage containers ready: these can be Sterlite plastic containers or Styrofoam boxes; or line a cardboard box with a plastic bag.
Obtain storage medium: such as newspaper, cedar chips, or vermiculite.
Either wrap clumps in newspaper and keep them in a plastic shopping bag (great for cold and humid basements) or carefully stack clumps in storage containers with a storage medium. Leave containers cracked open to allow condensation to escape.
Copyright © 2025 New England Dahlia Society. All rights reserved.
Dahlias in June: Common Pests and Diseases
As June warms up, your dahlias are really starting to put on growth, which unfortunately also makes them attractive targets for various pests and diseases. Early detection and treatment help maintain healthy plants ensuring great blooms.
APHIDS
How to Recognize: These small (1-3mm), soft-bodied insects can be green, black, pink, or even white. They typically cluster on new, tender growth, buds, and the undersides of leaves. Look for distorted or curled leaves, stunted growth, and sticky "honeydew" on leaves which can lead to sooty mold.
What to Do:
Strong Water Spray: A forceful jet of water from your hose can dislodge them.
Hand-Squishing: For small infestations, you can simply squish them with your fingers.
Insecticidal Soap: Apply an insecticidal soap solution (check label for dahlia safety) to affected areas, ensuring good coverage, especially under leaves. Repeat every 5-7 days if needed.
Natural Predators: Encourage beneficial insects like ladybugs and lacewings, which are natural aphid predators.
More Info: https://extension.oregonstate.edu/news/how-control-aphids-less-toxic-methods https://extension.umd.edu/resource/aphids-vegetables/
THRIPS
How to Recognize: These are tiny, less than 1mm, insects that are hard to see with the naked eye. Signs of their damage are silvery or bronzed streaks on leaves, distorted or stunted new growth, and discolored, often brown-streaked, or distorted flower petals, especially on lighter-colored blooms.
What to Do:
Hosing Off: Regular, strong sprays of water can help reduce populations.
Sticky Traps: Blue or yellow sticky traps can help monitor and trap adult thrips.
Neem Oil: Apply neem oil spray as directed on the label. It stops feeding and acts as a growth disruptor.
Pruning: Remove and dispose of heavily infested flowers or leaves.
More Info: https://ipm.ucanr.edu/PMG/PESTNOTES/pn7429.html
STEM BORERS
How to Recognize: This is a more serious pest. You might notice wilting of a single stem or an entire plant despite sufficient watering. Closer inspection might reveal a small hole (often with frass, a sawdust-like material) on the stem, usually at leaf axils. The stem might feel soft or hollow. Larvae (caterpillars or grubs) burrow into the stem, disrupting water and nutrient flow.
What to Do:
Pruning: If you identify a borer, prune out the affected stem well below the entry hole. Dispose of the infested stem far away from your garden or find and destroy the larvae inside the stem.
Vigilance: Inspect plants regularly, especially young ones, for signs of entry holes.
No Chemical Controls: Systemic insecticides are generally not recommended or effective for home garden stem borer control. Prevention is key.
More Info: https://extension.okstate.edu/fact-sheets/hla-6040-how-to-identify-and-managing-squash-bugs.html While focused on squash, the principles of recognizing borer damage are similar.
LEAF-EATING BEETLES: Asiatic Beetles, Japanese Beetles or other chafer beetles
How to Recognize: You'll see obvious holes in leaves, often irregular in shape. Asiatic beetles are the size and shape of a coffee bean but light brown. They only feed at night (check your plants after dark with a flashlight). Japanese beetles and other chafers feed during the day.
What to Do:
Hand-Picking: For smaller infestations, hand-picking beetles off the plants and dropping them into a bucket of soapy water is effective.
Row Covers: For young plants, physical barriers like fine mesh row covers can prevent beetles from landing on them.
Neem Oil: Can act as a deterrent.
More Info: https://www.umass.edu/agriculture-food-environment/landscape/fact-sheets/asiatic-garden-beetle
SLUGS AND SNAILS
How to Recognize: Are most active at night and leave irregular holes with ragged edges, especially on young leaves and new shoots. The most definitive sign is the silvery slime trail they leave behind on leaves, stems, or the ground.
What to Do:
Hand-Picking: Go out in the early morning or after rain with a flashlight to collect them.
Barriers: Create barriers with copper tape since slugs dislike crossing copper or diatomaceous earth. It needs to be reapplied after rain.
Traps: Beer traps such as a shallow dish filled with beer sunk into the ground attracts and drowns them.
Less Mulch: Keep mulch away from the immediate base of the plant, as it provides hiding spots.
Slug Pellets: Use iron phosphate-based products, such as Sluggo or Sluggo Plus which are safer for pets and wildlife.
More Info: https://www.rhs.org.uk/biodiversity/slugs-and-snails
Disease to Watch For
VIRUSES
E.g., Dahlia Mosaic Virus, Tomato Spotted Wilt Virus
How to Recognize: Viruses are spread by sucking insects like aphids and thrips or contaminated tools and fingers. Symptoms vary but often include:
Mottling or Yellowing: Irregular yellow or light green patches on leaves, often in a mosaic pattern.
Stunted Growth: Overall reduction in plant health and size.
Distorted Flowers: Flowers may be smaller, misshapen, or have unusual color breaks.
Ring Spots or Necrotic Areas: Circular patterns or dead spots on leaves.
What to Do:
No Cure: Unfortunately, there is no cure for virus infections in plants.
Remove and Destroy: Infected plants should be dug up and disposed of to prevent the spread to other dahlias.
Pest Control: Control insect vectors such as aphids, thrips to prevent further spread.
Sanitize Tools: Always disinfect pruning shears and other tools with a 10% bleach solution or rubbing alcohol between plants.
Source Healthy Stock: Purchase dahlia tubers and plants from reputable sources known for disease-free stock.
More Info: https://www.dahlia.org/wp-content/uploads/2022/06/Deborahs-Dahlia-Virus.pdf
Copyright © 2025 New England Dahlia Society. All rights reserved.
Part 2: Waking up Tubers for Cuttings ONLY
Copyright © 2024 New England Dahlia Society
February is generally too early to plant tubers indoors in pots
—> wait to pot up tubers until March/April - unless you have a heated greenhouse available
Timing for dahlia cuttings (approximate – differs by variety)
Waking up tubers: 2 to 5 weeks (some varieties need longer)
Root cuttings: 3 to 6 weeks (visible roots)
Grow on cuttings to planting size: 3 - 4 weeks
Continue reading the full article on cuttings. (with photos) here . Note the references are active links.
And just like that our thoughts turn to spring …. March 2025
Reminder, Long Island hardiness zone is now 7B with last frost predicted for the last week of April.
Part 1: Starting Dahlias from Seeds
Growing dahlias from seeds isn’t any harder than growing most other annuals from seeds. However, there are a few things to keep in mind.
The flowers of dahlia seedlings rarely look like their seed parents. Due to the octoploid genome (8 sets of chromosomes), countless combinations of different genetic traits can occur in seedlings.
Some of the dominant traits that tend to prevail in seedlings are open disc centers, low petal count, small blooms, tall plants, poor form, weak stems, downward facing blooms, or a single set of petals. Thus, most seed dahlias don’t look like the flashy big show dahlias most of us admire. But seed plants are usually much more vigorous and healthier than plants grown from tubers. They will do great in a garden border and are a fall favorite of many pollinators. Most seed dahlias will also make tubers that can be overwintered.
Desirable traits such as high petal counts, strong stems, good tubers, large blooms, and closed centers are far less common. It’s estimated that only 1 out of 1,000 seedlings has the right combination of desirable traits to become a show flower variety.
Seed germination typically takes between 3 days to 1 week and up to 2 weeks. However, due to the complicated genetics, even fat looking seeds might not sprout. Germination rates can sometimes be very low. Seeds can be pre-sprouted between wet paper towels in plastic bags to save space. Paper towels need to be checked daily and sprouted seeds have to be transplanted immediately and very carefully into pots with soilless growing medium.
Alternatively, sow seeds densely into soilless or seed starter mix and prick them out into larger pots as they germinate.
Dahlia seeds are very cold sensitive and should be started indoors 4 to 8 weeks before planting outside. Keep seedling trays or wet paper towels at a temperature of 70°F or higher.
Plant seedlings outside in late May. They should be well rooted and have at least 3 sets of true leaves.
Space plants 12 inches apart. If you want to increase the number of seedlings to evaluate, plant them 4 inches apart and then cull seedlings with undesirable traits as they bloom.
You can save your own seeds or buy seeds. However, many fully double show dahlia varieties make no or only few seeds. Therefore, high quality seeds from experienced dahlia hybridizers may cost $.50 to $2 for each seed.
Seeing a completely novel dahlia bloom, one you cultivated from seed, is a joy beyond measure.
Copyright © 2024 New England Dahlia Society.
All rights reserved.