Seasonal Articles 2025
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.
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.
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.