FAQ: Growing Season Questions

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Table of contents
» Pros & cons for planting dahlias in a perennial bed versus creating a dahlia bed
» When do I plant my dahlia tubers?
» Can I plant dahlia tubers in decorative pots?
» How deep should I plant my dahlia tubers?
» How far apart should the dahlia plants be?
» How do I keep track of the variety's names?
» How should I mulch the dahlia plants?
» How much mulch do I need to order?
» What are the best ways to water dahlias, and how much water to give?
» How do I support my dahlia plants?
» How do I 'top' or 'pinch back' my dahlia plants? Why should I?
» Disbudding: what is it, and how do you do it?
» How should I fertilize my dahlias?
» Could you explain foliar feeding, and when I should do it?
» How can I increase the vase life of my cut dahlia blooms?
» What can I do about bugs damaging my dahlias?
» What can I do about wireworms?
» How should I deal with white powdery stuff on my leaves?
» What can I do about animals destroying my plants?
» Compacted Soil
» What kind of question/answers are needed here?

Pros & cons for planting dahlias in a perennial bed versus creating a dahlia bed
If you are looking at the garden as a "picture", by all means mix it up--you can extend your season of color from earliest spring until late fall. Because of the heavy maintenance dahlias require, it is easier to use dahlias in a flower bed that is re-planted each year as opposed to one that is left in.

If your focus is on growing the finest dahlias, a monoculture bed is the way to go. It is much easier to irrigate, stake and maintain a group of just dahlias in a dedicated bed.

Read grower's comments to this question here:

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When do I plant my dahlia tubers?
There are three sure-fire ways to tell if it is time to plant dahlias outside:

1. It is after the last frost date for your region.
2. It is time to plant out tomatoes.
3. The soil registers at least 60 degrees Farenheit four inches down.

Bottom line: Dahlias want warm soil to grow in.

If you try to 'hurry them up' in cold soil, they are more likely to rot, get fungal diseases or just plain sit there doing nothing until warmer soil temperatures.

Read comments from some growers about what they look for before planting out:

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Can I plant dahlia tubers in decorative pots?
Yes, but the challenge is making sure they are watered, fertilized and supported adequately in the pot. Depending on your climate and the size of the pot, sometimes they need watered multiple times a day to once a day. The health and size of the plant can suffer if water and fertilizer requirements are not met, and it is quite easy to not keep up mantainance throughout the dahlia's long season.

Some bury the pot (from two gallon size to four inch size) into the ground to protect the tuber from underground critters and to make digging at the end of the season much easier. Watering and fertilizer demands are less when you bury the pot in the ground, as feeder roots can grow from below and above the pot into the surrounding soil to obtain what is needed.

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How deep should I plant my dahlia tubers?
Plant dahlias 4-6 inches deep.

Although the general consensus in the dahlia community is to bury the tuber four to six inches deep, there are lots of viewpoints on specifics:
1. using mounding to add depth over normal soil level
2. adding soil to the hole as it grows to allow warmth at root level
3. different depths for different plant sizes

Read grower's comments to this question here:

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How far apart should the dahlia plants be?
The standard answer is 18 to 24 inches for smaller varieties, and 24 to 36 for larger varieties. New growers should stick with these guidelines.

However, spacing can range from 6 inches to 36 inches apart, depending on what you are trying to do and your growing situation.

-If you are trying to maximize blooms from each plant, or they are in partial shade, you might want to space them on the wide side of the spectrum.
-If you are short on space, trialling different seedlings and/or varieties, or want to inhibit excessive root growth, you might want to space them on the short side of the spectrum.

Read how other growers are spacing their dahlias, and why they do it that way, here:

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How do I keep track of the variety's names?
In progress...

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How should I mulch the dahlia plants?
Mulch choices may vary by what is available in your region, and what your climate is like during the growing season. Read member's comments to get an idea of what you might look for.

Mulch options:

None (preen helpful, or scraping surface weeds with hoe)
Plastic with holes for plants (need irrigation system in place for season)
Landscape material
Alfalfa hay
Straw (seedless)
Grass clippings (some may disagree, as it is not composted)
Leaves (preferably aged so they won't blow away)
Aged manure (many growers stay away from horse manure because of the high weed seed content, preferring cow, chicken or guano)
Aged compost
Mushroom manure
Wood chips

What am I missing? Please let me know in the comments, and I'll add them!

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How much mulch do I need to order?
Two to three inches deep is standard.

Be aware that if your mulch choice is compost-based, it will most likely be well on its way to breaking down into the soil by fall. Normally, this is not an issue as the dahlia plants tend to shade out any weeds at that time.

Here's a helpful link to a calculator for how much material is needed to cover the garden:

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What are the best ways to water dahlias, and how much water to give?
Dahlias love having water always available to their roots, but can't survive long in standing water.

Here are the most common ways of watering, from half-hazard to most efficient...

-rain (depending on your area, this might be just fine with supplemental watering in dry weeks)
-individually soaked with a hose or buckets (tough to do on a consistent basis with good frequency over a three month time period, even with a few plants)
-overhead sprinkler (tends to waste water to evaporation, and can be problematic for water to reach roots when foliage is grown)
-ground-level sprinkler (some growers swear by it for keeping spider mites away from under the foliage, and water stays near the roots.)
-flood irrigation (weekly. Could not use with mulch, as it would wash away)
-leaky hose (used under mulch, with a slow drip to the root zone)
-t-tape with intermittent drip emitters (delivers water to each plant with low pressure. Very efficient, and the grower can put diluted fertilizer into the water)

Think your climate is tough? A grower in the desert area of Australia where temperatures are around 110-140 degrees has perfected 'pulse irrigation,' where the plants are watered and misted in fifteen minute pulses several times a day. This isn't for everyone, but check out what successful growers are doing in your area before deciding on the best solution for you.

Read the comments for grower's thoughts on watering, and chime in with your solution too!

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How do I support my dahlia plants?
Here are the different ways you can choose to stake/support your dahlias:
-Tomato cage (best for hard-to-reach plantings, or very few plants)
-Inverted tomato cage (more stable then the 'normal' direction, using stakes to secure the bottom)
-Bamboo poles (three ways- single thick one with main stalk tied to it / one pole per branch / three poles forming a teepee over plant)
-Rod, post or stake cut to 5 or 6 feet (tie main stalk and branches to it as the plant grows)
-Horizontal netting/fence (use posts to hold up netting/fence about 18 inches from ground, and allow plants to grow through it for support)
-Vertical netting/fence (use posts to secure netting up, and tie plants as it grows)
-Group roping (grow plants in rows, put posts on the corners & middle, and run twine or string all the way around the row at different levels to keep plants inside row)
-Combo horizontal netting with group roping
-Mounding soil at the base of the plants, and/or stopping each plant severely to keep them short

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How do I 'top' or 'pinch back' my dahlia plants? Why should I?
During the first month of growth, it is important to top the plant by pinching the middle growth out with your fingers, leaving four or five sets of leaves on the main stem. This forces the plant to grow 'out' instead of just 'up.' The plant will start growing branches from each leaf junction, and increase the number of buds the plant will develop at the same time.

Thumb of 2015-05-02/CCvacation/92debd
Borrowed from: http://www.thefriendsofmanito.org/images/GROWING_DAHLIAS_han...

This process is only needed to be done for the 'full sized' dahlia plants that grow three to eight feet tall. There are many bedding dahlias now being sold in nurseries as 'annuals,' and they typically grow one to two feet tall with no staking or topping needed.

Thumbnail by CCvacation
Click the image for an enlarged view.

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Disbudding: what is it, and how do you do it?
Disbudding is the practice of removing selected flower buds to allow the plant to focus on the remaining buds. This allows for longer, straighter stems and often a better-formed center bloom.

Typically, there are three buds at the end of each stem or the top of each dahlia plant. Most growers remove the secondary buds (or 'wing' buds) on either side of the center bud when they are the size of a pea or smaller.

If a stem is double disbudded (the laterals pinched out of the leaf set under the top bloom), the size of the remaining bloom is typically larger as more of the plant's energy is put into it.

Double disbudding is pinching out the wing buds AND pinching out the secondary buds that will start developing BELOW the primary bud in the second set of leaves. This allows for a nice long stem that can be cut down into the bush when the primary flower is almost ripe. It also assists the primary bloom to grow with more of the plant's resources, often leading to a higher petal count and larger size if disbudding is done when primary bud is the size of a pea or smaller.

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How should I fertilize my dahlias?
-Use a little balanced fertilizer every week, or use a time-release formula.
-Make sure the pH is around 6.2-6.5 so the plant can absorb the nutrients.
-Ensure there is ample water several times a week, and that it can drain freely from the soil.

"Like all plants, dahlias need sunlight, water and fertilizer. When somebody says they have difficulty in growing a plant each of those three ingredients must be correct. Assuming you get the tubers to sprout and get above the soil level, make sure they stay well watered(dahlias need more water than most plants), make sure they are in full sunlight(they hate full shade or even half shade) and that they have some fertilizer.

Just about any fertilizer will work, a little bit at a time. Too much is bad, too little is probably not likely if you fertilize them every couple of weeks with no more than a level tablespoon sprinkled at the base of the plant. If you are organic, you would use manure or bat guano, or blood meal, or leaf mold, or very rich compost before you plant and hope that there are enough nutrients for the plants for the entire season. If you (don't have too many), you can use Osmocote time release fertilizer and give them about 4 tablespoons per plant when you plant them and maybe one more tablespoon on August 1st. Once the plants are full sized(most reach 4 feet) stop fertilizing as they have enough to last the rest of the season.

Notice I did not say the formula for the fertilizer. That is much less important than the small doses of regular feeding. And you could use Miracle Grow once a week too, just make sure it is a weak solution. Fertilizer is plant food and just like human food you do not eat one meal each month but you eat every day. Plants too need small meals on a regular basis."
- teddahlia on Tue, Feb 18, 2014

"Pay no attention to the myth that dahlias do not need nitrogen. All plants need nitrogen and without nitrogen dahlias grow very poorly. The myth goes back to when people were over fertilizing dahlias in the Fall and too much nitrogen in the Fall does affect tuber storage but does not affect the quality of the blooms. In my fertilizer recommendation above, you will note that the fertilizer is drastically reduced in early Fall. Any fertilizer that you use must have nitrogen. As I said just about any formula will do as long as there is some of all three nutrients. They are abbreviated as NPK and the first number is nitrogen the second phosphorus and the third potassium. Having all three gives the plants a balanced diet. Osmocote is always formulated with enough nitrogen and all the major elements and as a bonus it includes the minor elements needed for plant growth."

One of the most important things about fertilizing is to make sure the pH is as close to 6.2-6.5 as possible, which allows your dahlia plants to take up all that fertilizer you're throwing at them.

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Could you explain foliar feeding, and when I should do it?
Foliar feeding is the light spraying of diluted liquid nutrients/fertilizer on the leaves of plants to encourage growth.

It is recommended to apply foliar feed diluted, lightly and often. Best done when sunlight is not on the plants, as it can scorch the leaves as droplets act as magnifying glasses. Most growers spray during cloudy days or in the early evening.

The benefits to foliar feeding are thought to be: it bypasses the root system that is dependent on a balanced soil to properly metabolitize nutrients, it uses less fertilizer then would be needed if applied to the soil, it avoids fertilizer buildup in the soil, and compost teas are thought to be most effective applied to the leaves. (There are mixed opinions in the scientific world, with no fully accepted benefit of foliar spraying. There are many growers that swear by it, however.)

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How can I increase the vase life of my cut dahlia blooms?
See what other growers say about preserving vase life HERE:

Please comment on methods that has or has NOT worked for you!

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What can I do about bugs damaging my dahlias?
Four main methods of pest management
-systematic/straight pesticide
-good bugs (importing or supporting lady bug, praying mantis, hover wasps, etc)
-'natural' sprays (water, horticultural oils, ammonia, etc.)
-manual removal of pests (by hand, tool or pet poultry)


Systematic/straight pesticide
Many growers see pesticides as a last resort, if nothing else works. It's similar to swatting a fly with a sledge hammer-you might get the fly, but what about the lasting collateral damage to the wall behind the fly? In other words, most insecticides kill both the predator and nuisance bugs, which often ends up causing a sharp increase in the nuisance bugs after the insecticide wears off, with the predator bugs not able to recover as quickly. Predator insects typically keep other insects in balance, and without them, the other insects thrive.

Nuisance bugs

-squishing with gloves/knocking into pail of soapy water
-using rolled up damp newspapers (or empty half grapefruit, or low containers of beer) to trap them at night, disposing of them in morning
-Sluggo Plus (works on first population waves of slugs and earwigs if set out early)
-systematic pesticides

-squishing with gloves/knocking into pail of soapy water
-using rolled up damp newspapers (or empty half grapefruit, or low containers of beer) to trap them at night, disposing of them in morning
-spray diluted ammonia water on plants, or directly on slugs
-diatonic earth (spelling!)
-Deadline poured in a line or circle around the plants, and it paralyzes the slug before killing.
- Sluggo bait sprinkled around plants in spring before shoots are out of ground, or when just planting out. After consumed, you will see orange slime trails in one species of slug as it dies.

Japanese beetles
-drowning in soapy water by knocking pests into bucket
-pheromone traps (some say that this just draws more to your garden)
-systematic pesticides
-Milky Spore added to lawn and garden-- it is a nematode that preys on grub beetles, and takes a long time to take effect.

-importing or supporting lady bug populations
-spraying infected plants with strong stream of water (once aphids fall off, they can't climb back up)
-spray diluted ammonia water on plants, or directly on aphids
-oil sprays (neem, horticultural or vegetable oils)
-systematic pesticides

Spider mites
-use a sprinkler directed UNDER the plants to water. Spider mites prefer hot, dry conditions.
-there are more tips below in the comments, but haven't been listed in this summary post yet.

-buy a cheap, plastic bucket, cut it into strips, wipe a quantity of detergent on each strip and hang them in trees around the dahlias. "You'll gradually get the whitefly numbers down and even catch a few other things while you're at it, like thrips and mites. Couldn't be easier."
-use a sprinkler directed UNDER the plants to water. Whiteflies prefer dry conditions.

Check out more details on the four main methods of pest management HERE: http://cubits.org/Dahlias/thread/view/80296/

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What can I do about wireworms?
There are many types of wireworms. There are species on the west coast in the US and Canada are nasty to dahlia tubers, but the species of wireworm dominate on the East coast tend to prefer eating grass crops over tuberous crops.

If you are experiencing continued damage to your tubers, you can check with potato lures by putting the cut-side of potatoes down onto the soil, and checking after 12 hours for sign of the tiny worms burrowing in.

There are three potential solutions for wireworm infestations:
- purchasing the beneficial nematode, Steinernema Carpocapsae, and releasing them in several applications over several years for bad infestations
- flooding the planting zone with water (google for specifics- there were several studies on this by universities)
-seeding the area with brassica (especially mustards and oil radish) as a manure crop and tilling in before planting dahlias (supposed to repel the wireworms from the area)

Please read the comments for specific directions on nematodes.

Do you have another solution? Please add it to the comments, and help your fellow growers!

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How should I deal with white powdery stuff on my leaves?
Powdery Mildew is a fungus that tends to hit from end of July through September, associated with hot, muggy weather.

There are a variety of strategies for avoiding or reducing the impact of PM:
1. Mulch (the spores overwinter in the soil, so covering the soil can reduce infection)
2. Air circulation (space the plants so the adult branches won't touch / take off the lower branches up to 18 inches from the ground, as well as inside branches that are too crowded)
3. Prevention/ intervention
- low fat milk spray
- baking soda with water spray
- fungi-eating bacteria spray (shop for 'beneficial microbes for plants' for product names)
- horticultural oil sprays
- fungicide chemical sprays

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What can I do about animals destroying my plants?
1. Identify the type of animal causing the damage
2. Take appropriate action to discourage the critter

Damage Sign

Dug up plants
(Full tuber and plant thrown up to three feet away from planting site with no nibble marks on plant)
Normally this is caused by raccoons, skunks or dogs looking for the bloodmeal or bonemeal used during planting the dahlia.

Demolition from the top down
Top munched down, lots of missing plant, very little plant debris left on ground
Groundhog, deer... Look for golf-ball size holes in the ground around plants- they might actually be deer tracks if ground is soft.

Plants 'cut' and toppled
Tops of plant laying on the ground with or without nibble marks, with stem sliced at an angle about one to four inches from ground
Rabbits, who like to taste-test before eating at the buffet. Often the severed plants can be rooted if found early, and if the rabbit hasn't developed a taste for dahlias yet. (Can also be cutworm if cut is lower to the ground and is not sliced at an angle.)

Tubers are gone, leaving a wilted plant in place
Gophers or voles... Check by looking for tunnels and remnants of tubers for rodent gnaw marks

Possible Solutions

Do nothing
Seriously, some critters just move on by themselves, or it's an acceptably low amount of damage. So you're not a zen master? Then read on...

Stinkify the area\plants
Tie the stinkiest and cheapest dryer sheets you can find to stakes, fences, tree branches all around the area you don't want critters. Hard to appreciate a good meal if it stinks to high heaven. Along the same lines, try the expensive sprays or make your own with cayenne pepper, etc. Some use blood meal around the plants to scare off the herbivores, but this can just attract curious raccoon and skunk to your garden. Do not use things like coyote urine, as it attracts more coyotes. Human urine might work, though. Some zoos sell 'zoo poo,' with a mix of predator feces that can be spread about to deter prey animals from hanging around. You can try sachets of stinky soap, human hair or toss some mothballs about. However, don't expect stink to work alone if animals already have a taste for the great buffet you've put out for them.

Scare the critters away
Use aluminum pie pans, old CDs, sparkly ribbons tied to a rope dangling in a breeze, or put out little pinwheels that sparkle and clank in the wind. Install a motion detector water sprinkler to pelt the critters, or put a bucket over a constantly playing radio with an outside-rated cord. Let a dog have the run around the garden, for that personal 'stay out' bark delivered to each ousted critter. Or just stay out in the garden all the time waving your arms furiously every time an unwanted critter sniffs near the garden. Again, if they know the feast is waiting because they already started the first course, scaring may not be very effective by itself.

Protect the perimeter
No one wants the added expense or eyesore of a fence, but well-installed ones can keep out rabbit, groundhogs and deer. Typically, a two foot fence hugging the ground or a three foot fence with six inches bent on the ground away from what you are protecting will dissuade rabbits- they could jump it, but most won't bother. Groundhogs need at least three foot high from the ground with one foot of fence buried to keep them out once they taste what you are protecting. For deer, only an eight foot fence will fully protect your garden, but many deer have little interest in dahlias and easier methods might work for a lot cheaper. For gophers and voles, this means planting in pots to protect the tubers.

Attack their homes
Find out where those groundhogs and rabbits are living, or find the main tunnels of the underground rodents. Toss in handfuls of mothballs like grenades. Block it up if you know they are gone, and make them look for a more friendly neighborhood to bother. Flood them out. Spray yucky stuff in their holes that stink to high heaven. Make it as uncomfortable as you can so they move on.

Attack them
Killing traps or catch/release for the 15 lb or under rodents. Poison if nothing else works. Pellet guns for rabbit/groundhogs and rifles for deer if necessary. Hopefully this is a last resort for you that will not be necessary.

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Compacted Soil
admin note: this was split from the fertilizer thread, and needs a clear answer HERE.

Please comment on:
What are some ways to deal with compacted soil, and how does pH enter into the discussion?

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What kind of question/answers are needed here?
Do you have a 'Growing Season' question that hasn't been answered? Please ask it here!

Some topics that still need to be discussed:

Animal Management
Bloom care in a vase
Virus Management

Permalink / 3 comments

Other FAQ pages that may help you:
» Help! I'm new here... What do I do?
Learn the best places to check out first on this forum!

» Dahlia Basics

This FAQ provides VERY basic info on what a dahlia is and how to tend to them, directing folks to links for more details.

» Pre-Season Questions

Quick answers on how to pre-start tubers, take cuttings, starting from seed, etc.

» Post-Season Questions

Quick answers on digging, dividing and storing dahlia tubers

» Hybridizing Dahlias- Basics

Currently open to Cubit Members & Active Members.

» Hybridizing Dahlias- Advanced

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