HOW TO GROW DAHLIAS

DAHLIA TIPS & CARE

RECEIVING
PLANTING
STAKING
MONITORING FOR PLANT HEALTH, PESTS & DISEASE
PINCHING, DISBUDDING, & DEADHEADING
SEEDS
DIGGING & STORING

RECEIVING DAHLIA TUBERS

• Often you will get your tubers before your frost free date. Store them properly until you can plant them (a cool, dark area like a cold room). Ensure they do not freeze!
• Optional! You can get them growing a few weeks before your frost-free date. Start them indoors in front of a bright sunny south-facing window or under grow lights at average room temperature. Place them nestled on slightly damp potting soil. Do not water until new roots develop. If over watered, the mother tuber may be inclined to rot (just keep the medium slightly damp). Remember to harden off the plants before you move them outside permanently. Ensure the risk of frost has passed. To harden off, move them outside for a few hours at a time as the weather permits. Avoid placing in direct sunlight during the hottest part of the day. Let the breeze and gentle sunlight toughen up the young dahlia plants.

PLANTING DAHLIA TUBERS

• Dahlias grow best in fertile, well-drained slightly acidic soil (amend with compost, manure, fertilizer as needed). They can be grown in pots or raised beds. If growing in pots, the pots should be at least 5 gallons in size.
• Remember dahlias need approximately 4 months (120 days) to develop “storage worthy” tubers… so aim to have your tubers planted as soon as it warms up and preferably before the beginning of June.
• Choose a sunny location (they can tolerate some shade during the day but do best in full sun all day long).
• Tubers can be planted outside after the risk of frost in your area has passed. Keep an eye out for the lilacs blooming! When the lilacs start blooming its a good indication that the time is right to plant your dahlias. Mid-May in Terrace, BC is usually frost free.
• Initially, water only if soil is not already damp. Regular watering is only necessary once the tubers have sprouted and the new growth has started to develop roots. Too much water early on can promote rot in the mother tubers.
• We plant individual tubers of the same variety in groups of 4. Approximately 4-6″ deep and 9″ apart in the shape of a square. We space each “square” 1 foot away from the next square of the same variety, and give a little more space if the next square is of a different variety.
• When your dahlias have 3 to 4 sets of true leaves, you should pinch out the central tip. This will encourage branching and more blooms!
• Water and fertilize as necessary throughout the season (how often really depends on your growing conditions).

STAKING DAHLIAS

• Most dahlias benefit from a supportive stake. Shorter varieties may not need staking and are also best suited for growing in pots, grow bags, or raised beds. Plants that are grown without support can be at risk of falling over or having stems break.
• If you’re growing for cut flowers, staking/supporting your dahlias such that they stand straight up will help produce more useable stems for bouquets. Dahlia plants that lean/fall over will reach for the sun, producing stems that bend the wrong way (and don’t unbend) making them difficult to use in the vase.
• Types of stakes – your choice may depend on your budget and what is readily available.
  • Bamboo stakes are relatively inexpensive, work well enough, but won’t last forever and can be a bit flimsy. They can look more natural and aesthetically pleasing in the garden.
  • Fibreglass stakes – more expensive. The smaller diameter can be a bit flimsy, so get the largest diamter/thicker stakes you can find. They can last a long time.
  • Hardwood stakes – more expensive than bamboo, but sturdier and will last longer. They tend to blend into the garden with ease.
  • Rebar stakes are heavier duty and will probably last your lifetime and longer. The ends of “short” rebar stakes can be a real hazard in the garden. Safety first – be sure to place a protective cap on the end (even a small length of old garden hose can work to prevent injury)
  • T-fence posts are heavier duty and will probably last your lifetime and longer too. Excellent for farms. A little on the industrial side for pretty gardens!
  • Electrical conduit are heavier duty and will probably last your lifetime and longer too
  • We prefer 7′ lengths

MONITORING DAHLIAS FOR HEALTH, PESTS, & DISEASE

• As your dahlias grow, you’ll want to keep an eye out for plant vigour, weeds, pests and disease.
  
• PLANT VIGOUR – Healthy, vigorous plants look and do best and are more resistant to pests and disease.
  • Fertilize and water as necessary.
  • If a young plant looks wilted, a rotten tuber could be the cause. Gently remove the soil around the plant to check the tuber for rot. If you find the mother tuber is mushy and rotting, remove as much of the rotten tuber as you can. Leave just the young plant with any roots that have developed. Then gently repack the soil around the base of the plant. If the plant does not perk up, remove it from your garden (“if in doubt, throw it out”).
    
• WEEDS
  • Minimize competition by keeping your dahlia patch weed free – this will help your dahlias thrive. Weeds can crowd out your young dahlia plants and rob them of nutrients.
  • Mulching can be helpful, especially if you live in an area with hot dry summers. It keeps weeds at bay and helps keep moisture in the soil. We don’t mulch. Instead we keep the weeds in check by regular hoeing or cultivating. Once the plants are established they’ll start to shade out the weeds.
    
• PESTS – commonly include slugs, aphids, thrips, tarnished plant bug, cutworms & caterpillars, leafhoppers and earwigs.
  • Slugs love to munch on young dahlia plants. We control them primarily by keeping a clean garden. It is most effective and doesn’t cost a penny. A clean garden reduces unintentional slug habitat. Debris piles, pots, wood and tarps left on the ground are examples of places where slugs hide and lay eggs. The best time to find slugs on plants is the early morning or late evening. If you notice slug damage on a plant but can’t find any slugs, place a trap near the plant. A scrap piece of wood placed over a depression in the soil makes a good slug trap. The slugs use the trap during the day. Remember to check the trap during the day and remove the slugs. Remember to remove traps no longer needed or else they become breeding grounds for more slugs! Pop slugs into a bucket of salted water or snip them in half with garden shears to eliminate them. Slug bait can also be used to help control slug populations.
  • Cutworms feed on young plants at or below the soil level. If you see leaves or young seedlings that appear to be “snipped” off at the soil level, there is likely a cutworm hiding in the soil an inch or two away from the stem of the affected plant. Finding & eliminating the cutworm is essential to prevent further damage. Gently scoop up the soil from around the stem and then scatter it on a board or pathway to shake out the culprit. Cutworms are grey/brown in colour and curl up when disturbed. They can be smaller or larger – about 1/4 of an inch to 1 1/2 inches long. Spring application of beneficial nematodes may be used as part of a strategy to control cutworms and other pests such as wireworms.
  • Aphids, thrips, earwigs, leafhoppers and caterpillars can be controlled with an insecticide like Safer’s End-All or Ortho Bug Be Gone. Neem oil may also be used for some pests. If caterpillars are the main problem, BTK is a good option that can be more cost-effective.
    
• DISEASES – Fungal, bacterial, viral.
  • Prevention is the best method to reduce and eliminate disease.
  • Be familiar with symptom and signs of disease. Some helpful links:
    • https://www.dahlia.org/docsinfo/understanding_virus_in_dahlia/
    • https://blog.longfield-gardens.com/dahlia-pests-and-diseases/
    • https://www.greenhousegrower.com/production/crop-inputs/how-to-prevent-leafy-gall-before-you-lose-plants/#slide=67339-67283-1
  • Subscribe to the philosophy “if in doubt, throw it out”. Only share tubers that you know to be disease free.
  • Keep your tools clean (dip your tools in 10% bleach solution between plants).
  • Keep pests under control – some can spread disease between plants.
  • Avoid mechanical and environmental (i.e. support/stake dahlias to mitigate wind breakage) damage to your plants. Wounds can be an entry point for disease.

PINCHING, DISBUDDING, & DEADHEADING DAHLIAS

• PINCHING– the practice of removing the tip of the central stem to promote a bushier, sturdier plant with more lateral growth and more blooms. Pinch plants when they are approximately 12″ tall, leaving 3-4 sets of true leaves (use snips, or fingers to pinch off the central stem just above the junction of the 3rd or 4th set of true leaves). Plants that are not pinched, will still produce beautiful blooms, but you won’t get near as many blooms to enjoy.
• DISBUDDING – the practice of removing lateral buds to promote longer stems and better blooms. Some varieties will require more debudding than others, but generally speaking, a little debudding goes a long way.
  • If you use shorter stems (I often need shorter stems for bouquets), you may want to experiment with removing the central bud instead. I like to experiment to see what works best for me 🙂
• DEADHEADING – the practice of removing spent blooms. Removing spent blooms will encourage more blooms! Blooms will last for many days in the garden. When they start to look a little ragged – they start to show their yellow central disc, the petals start to fade (from back to front), turn papery, wilted, and brown – they need to be removed to encourage more blooming. Snip or break the spent bloom off the top of its stem and move it to your compost. If you’re keen on collecting dahlia seeds, do not deadhead.

DAHLIA SEEDS

• Dahlias can be grown from seed, but you may need to alter your expectations because the seeds are unlikely to produce the same bloom as the seed parent. The only ways to grow a dahlia with the same characteristics/genetics as the parent is by taking a cutting from the parent, or by growing a new plant from a tuber of the parent. Dahlias tend to revert to to their less appealing dominant traits (open centres, single blooms, very tall plants…).
• Some dahlias are great pollen producers, some varieties are great seed producers, and some are great at both or neither.
• Instead of deadheading, leave spent blooms to form seed pods – seeds take approximately 4-6 weeks to ripen after pollination occurs.
• If you get a lot of rain, you can help reduce chance of seed pods rotting by gently squeezing the water out of them.
• SEED COLLECTION – Ripe seed pods should feel somewhat solid/dense/heavy if seeds have developed within. More so for good seed producers than for those that produce few seeds. Collect ripe seed pods, and place them somewhere warm and dry where they can dry out in a single layer. When the pods are completely dry, the seeds are easily removed.
• GROWING FROM SEED – Start seeds indoors 4-6 weeks before your last frost date (you can start them earlier if you have space to grow them on indoors or in a heated greenhouse where they are protected from subzero night temperatures). Germination rates can vary a fair bit… they tend to be lower for double blooms and higher for single blooms. Seeds will take ~7 to 10 days to germinate at room temperature (~21 degrees C, or 70 degrees F). Your indoor space may influence how you decide to start your dahlia seeds. If you’re short on space, you may wish to use the “paper towel” method whereby you germinate the seeds between moist layers of paper towel, then plant only the seeds that germinate in cell packs or small 2-3″ pots under grow lights. Ensure that the paper towel doesn’t dry out. Dahlia seeds can also be started in moist potting mix (I like https://www.sungro.com/retail-product/sunshine-mix-4/ ). Fill a tray with the potting mix, moisten, then sprinkle the seeds across the top, then sprinkle no more than 1/4″ of moist potting mix over the dahlia seeds (cover tray with a clear plastic dome to maintain the moisture until seeds have germinated, then remove). Transplant seedlings into cell packs or small pots after they develop their first set of true leaves. As the plants grow, you may wish to pot them up into successively larger pots. If your goal is to have lovely tubers, ensure that the seedlings aren’t constricted by the size of the pots while you’re waiting for your last frost free date, else you’ll end up with more of a “pot tuber” (still totally viable for producing shoots the next season, but the appearance is more like a small clump the size of the pot). Watch the weather forecast – as it gets closer to your frost free date you can begin to harden off your tender seedlings by putting them outside for a few hours each day (avoid direct sunlight, and avoid mid-day sun). After your seedlings have been hardened off, and your risk of frost is in the rear-view mirror, transplant the seedlings out into your garden and grown them on as you would if growing from a tuber…

WINTERIZING DAHLIAS – DIGGING & STORING

• Dahlias are not hardy. The tubers do not tolerate freezing and thus must be dug up and stored over the winter in most of Canada. In areas like Vancouver BC where winters are often very mild, some folks have success leaving them in the ground. If you choose to leave your dahlias in the ground in Canada, be prepared to lose them all to freezing! It is a real risk.
• In the Terrace, BC area (zone 5 with pockets of 6-7) we start the “digging” process in October. Remember that the earlier you dig, the longer you’ll need to store the tubers. If you leave it too late, you might find it rather cold and miserable to be out digging, or you might run out of time if you get a snowfall or the ground freezes! Some folks like to wait until the first hard frost kills off the plants – this is not necessary. If your dahlias have been growing for at least 4 months (~120 days), you can start lifting them.
• Things you’ll need:
  • Your favourite shovel for digging
  • Water/hose for washing off your tubers
  • snips for trimming/cleaning up tubers (I like to have 2 pairs, so that one can be disinfected while I use the other)
  • loppers or cordless reciprocating saw for cutting down stalks and splitting big clumps
  • bleach solution for cleaning tools
  • storage boxes
    • Plastic (remember that plastic doesn’t breath – check periodically for condensation and ventilate if necessary)
    • Cardboard (breathes nicely)
  • storage medium – remember that different mediums may work better for some folks than others depending on moisture levels of the medium, humidity level during storage, and storage temperatures. Note about storing: There are many different ways to store dahlia tubers successfully. Location, humidity, temperature, ventilation, and storage medium play roles. You’ll need to find what works best for your circumstances. Some dahlia varieties have amazing tubers that store really well no matter how they are treated, while others do not! My Boppa used to store his clumps of dahlias on their own without any storage medium in cardboard boxes on the cement floor of an old house with a cool basement with great success!
    • peat moss (inexpensive and readily available in the Terrace BC Canada area)
    • wood shavings (inexpensive and readily available from farm supply or pet stores or maybe even a local sawmill if you’re lucky. We have not used wood shavings for long term storage ourselves – we’d suggest being cautious that they don’t cause your tubers to shrivel)
    • vermiculite (expensive and harder to find in large volumes in the Terrace area – we have not used it, but many people do with good results)
    • perlite (Expensive and harder to find. Very dusty to work with – wear a mask! Works well for areas with high humidity. If humidity is too low, tubers may desicate)
    • newspaper (roll individual tubers tightly to block air and light, then pack rolled tubers into a cardboard or plastic box. Works well on a smaller scale. Watch out for mold if humidity is too high, or desication if humidity is too low)
    • seran wrap (roll individual tubers – we do not use or recommend this method because we avoid unnecessary single use plastic where we can)
  • a cool, dark place that doesn’t freeze to store your tubers (aim for 5 degrees celsius).
• Steps to follow:
  1. Strip the lower the leaves from the plants in September. If you keep track of your varieties, this is a good time to ensure all your plants are labelled while they still have blooms.
  2. A week before you intend to start digging, cut the stalks down leaving 4-6 inches of stalk above the ground (enough to easily grab to pull the clump out). Leaving the clumps in the ground for a week or so can make the “eyes” more obvious as they swell up. It may or may not improve storage success – know that it is not critical. If circumstances are such that you need to dig right after cutting the stalks down, you can do that. If its going to rain a lot, you may wish to get them out of the ground sooner than later especially if your soil is heavy or doesn’t drain as well as you’d like. Remember, this is a good time to be on the look out for disease such as leafy or crown gall that if present can sometimes be noticed around the top of the clump.
  3. Time to dig! Using your favourite shovel, cut a circle around each clump. Insert the shovel at a bit of an angle so that it severs the roots from the tubers under the clump. For a large clump, you might make 4-5 cuts at a bit of an angle with the shovel to circle the clump. Try to avoid slicing thru the tubers (if you cut thru a good tuber, just let it air dry for about 24 hours to heal over and it should store just fine). Now that most of the roots are severed from the tubers, grab the stalk and lift the clump with the shovel at the same time, pulling the clump out of the bed. If you yank the clump out of the ground without severing the roots, you risk breaking necks on good tubers. If your soil is really heavy, you may also want to brush away the bulk of the heavy dirt from the crown area before lifting to help preserves those necks. Some varieties with long skinny necks may require a bit more finesse than those with robust “no neck” tubers.
  4. Inspect the clump for anything that looks like disease. With the hose, gently wash the dirt off the clump.
  5. Decide if you’re going to split the clumps into individual tubers now or wait until spring. I almost always split the clumps in the fall as it requires much less space to store them. If a clump is quite small with a small crown that might be too small to split without damaging, I will leave it until spring to split. If you have a lot of space or don’t have many dahlias, you may wish to store clumps whole and split in the spring – that works too.
  6. Split the clumps into individual viable tubers (each tuber must have an “eye” – a bit of a bump on the crown from which a new stalk will grow in the spring). Not all of the tubers will produce a new plant. On average, a clump from a single stalk may give you 4-5 viable tubers with eyes that will produce new plants. Some varieties produce a lot more and some less. Plants grown from tubers usually produce twice as many viable tubers as those grown from cuttings. The viable tubers are found attached to the crown or sometimes the base of a stalk… many of the tubers around the bottom of the clump, or tubers growing off another tuber, will be blind (without an eye) and will not be able to produce a new plant. They can be discarded in the compost bin. If your clump was grown from a tuber (rather than a cutting) you may also need to cut away the “mother” tuber. The mother tuber is usually fairly easy to spot – its usually darker, bigger, and may sometimes have a bit of rot. Sometimes the mother tuber may not be present if it rotted away earlier in the season. On occasion, your dahlia may not be a good tuber producer and you might only end up with the mother tuber and few smaller tubers. If this happens, you can attempt to keep the mother tuber and hope that it doesn’t rot over the winter in storage.
  7. Let the split tubers air dry and heal over for approximately 24 hrs before storing. If you leave tubers out of cold storage too long, they may start to soften and shrivel (some varieties are more sensitive than others).
  8. Pack the tubers into either cardboard or plastic boxes with your storage medium. We use peat moss for our storage medium (because its readily available in our area) in plastic containers. The peat moss should be drier than damp. If too damp, the risk of rot increase. Pack the tubers loosely in layers such that they are separated from one another by the storage medium.
  9. Move your boxes of tubers into your cold dark winter storage area.
  10. Throughout the winter, check on your tubers periodically. Check for condensation that requires ventilation. Check for desiccation which may indicate humidity is too low or temperatures too high. Make adjustments as necessary.

HOW TO DIVIDE A CLUMP OF DAHLIA TUBERS