Most dahlias will be blooming, on average, 90 days after planting. The earliest blooming dahlias will be most of the Low Growing Dwarf dahlias and early blooming varieties, which will bloom approximately 75 days after planting. While the larger blooms (8" bloom size and larger) will take approximately 120 days from planting to bloom. The great thing with dahlias though regardless of when they start to bloom is that they will bloom through frost. However, this bloom time greatly depends on the growing environment including weather, deep watering, fertilizing, and overall care given.

Watering is the #1 problem we see when dahlias are not growing and blooming properly. They do not need to be watered at planting time in most areas but need lots of deep (8-10" deep) watering to reach the roots once they sprout above ground level. The exception will be in very warm, dry areas, where light watering at planting is needed (about once a week) until the dahlias have emerged. Most areas have an adequate amount of rainwater to get dahlias
off on the right foot. Once the dahlias are above the ground and established, they will require deep watering 3-4 times per week for 60+ minutes by sprinkler or soaker hose, and even longer in the heat of the summer. In containers, you will need to be watering 1 – 2 times per day until the water runs out the bottom of the container. Deep watering means the water will reach down eight or more inches to the planted tuber's roots. Hand watering is not enough, nor is it a method we recommend! Watering deeply three times a week is better than watering lightly 7 times a week, as the water will not reach the roots, leaving you with a green plant and little to
no blooms. Please keep in mind your climate will determine the amount you will need to water. Adequate deep watering is required for proper growth and blooming. Most rain showers will not penetrate the soil deep enough for adequate watering. If you are growing in containers, please see container growing instructions for recommendations. Please remember you must adjust your watering schedule each year depending on the weather and the plant’s needs. Hand watering with a hose or watering can is insufficient for dahlias and will not allow the water to get deep enough to their roots.

Use Low Nitrogen Fertilizer

We recommend a low-nitrogen fertilizer, usually referred to as a bloom food. For dahlias, there are two options, one is processed/bagged steer or cow manure, and the second is commercial fertilizer. We recommend using a combination of both. Dahlias require low-nitrogen fertilizer. We recommend using a fertilizer with a higher percentage of potassium and phosphorus. A good rule of thumb is to look for a fertilizer where the first component number (nitrogen) is 1/2 of the other two numbers. Usually, a bloom food or vegetable-type fertilizer will have these similar numbers. The first application should be 30 days after planting and repeated every 3-4 weeks throughout the season, about 1 time per month. If growing in containers, you will need to fertilize every 2 – 3 weeks, as the fertilizer is washed through the soil quicker. Please remember that during extreme heat or any event causing stress to your plants, you will need to fertilize more often, as they will use the fertilizer quicker.

Cow/Steer Manure

Cow/steer manure is an excellent way to enrich your soil, as it is perfect for dahlias. It can be applied any time prior to planting, during planting, or throughout the growing season. It will amend and lighten your soil along with fertilizing. If you choose steer manure it must be processed/ bagged manure. The only recommended manure is cow or steer, as all other animal manures are too rich and will burn the tubers. If you want to add fresh steer manure, add it in the fall, this will allow time for it to break down prior to spring planting. If your plants aren't thriving, they need more fertilizer and/or more water.

Commercial Fertilizer

All commercial fertilizers contain a 3-number component series. The first number indicates the amount of nitrogen, the second number indicates phosphorus, and the third number is potassium (potash). We recommend fertilizers low in nitrogen and high in potassium and phosphorus. We like to see the first component half, or less than half, of the second two components. Examples would be 2-4-4, 3-9-4, 4-10-7, 5-10-10, 2-15-15, 8-16-16, 6-30-30. Any fertilizer close to these numbers will work great! The second two components do not have to be exact matches; just as close as you can get. Look for a bloom food that mentions that it is a bloom booster or promotes blooming. We recommend avoiding Miracle-Gro products as most are too high in nitrogen. The first fertilizer application for your dahlias should be about 30 days after planting and repeated every 3-4 weeks throughout the season for dahlias planted in the ground and every 2–3 weeks for dahlias planted in containers. Follow the manufacturer’s directions on the application amount. One of the biggest mistakes with dahlias is overfeeding them with a high-nitrogen fertilizer.

Avoid all high nitrogen fertilizers

One of the biggest mistakes made with dahlias is overfeeding them with “high nitrogen” fertilizers. Avoid high nitrogen compost and high nitrogen water- soluble types (Miracle-Gro - or anything with triple digits matching or the first number higher than the other two numbers is too much nitrogen i.e; 16-16-16, 18-18-18, 15-0-0, 20-5-5, etc.) as they promote weak stems, huge green plants, small blooms, blown/popped centered blooms, or no blooms, and tubers that rot or shrivel in storage in most cases. Although we standardly do not recommend a triple 10, 16, or 20 fertilizer, it may be used once or twice in a growing season if your dahlias have yellowing leaves or are slow to grow. Nitrogen may be needed to give your plants a boost.

Only use zero nitrogen (ex: 0-10-10 Alaska Morbloom) late in the season. A fertilizer with zero nitrogen (the first number in the 3 digits listed on a fertilizer), such as 0-10-10, should only be used late in the blooming season to increase bloom. Do not use a zero-nitrogen fertilizer early and mid-season as your dahlias need some nitrogen to grow and be green.

Dahlias will hibernate if they are not receiving proper water or fertilizer. If your dahlias are green plants lacking blooms, they are most likely waiting for more water, food, and/or direct sunlight. Dahlias require deep watering 3-4 times a week by a soaker hose or sprinkler for 60+ minutes each session when planted in the ground, as the water must reach the roots, which are 8-10” deep or watered at least 1-2 times daily if planted in pots. Hand watering with a hose or watering can is insufficient for dahlias and will not allow the water to get deep enough to their roots. Dahlias also require low-nitrogen fertilizer, which should be applied about every 3-4 weeks for in-the-ground plants and every 2-3 weeks for dahlias growing in pots. They also need 6-8 hours of direct sunlight daily to thrive. If your dahlias are struggling in the summer, please give them 1 dose of high nitrogen fertilizer and ½ cup of Epsom salts (per plant) to help them take off. Two weeks after the one application of high nitrogen fertilizer, you may repeat the high nitrogen dose and Epsom salts if your plants have not improved. Alternatively, you may switch back to low nitrogen fertilizer and apply it every 3-4 weeks. Please increase your water if you are not giving them the suggested amount per our recommendations. They should take off in 10-14 days once our recommendations are followed. Remember, rainwater is not sufficient for watering your dahlias.

We recommend staking any dahlias that have a height of 3 feet or more. The best time to stake your dahlias is during the planting process. This will avoid unnecessary damage to the tuber later. Any staking product will work, including tomato cages, metal rods, bamboo stakes, etc. We do offer stakes, view our stakes here or visit our gift shop at the farm to view the options available.

We recommend topping all plants over 3' tall to promote shorter, stockier plants with better stem length for cutting. Pinch or cut the center shoot just above the third set of leaves or when the plant height is about 18- 20" tall. This is just a one-time pinch, as we recommend continuing to deadhead your old flowers all season long. Please see the diagram or video below for additional information. If, at any point, your dahlias are too tall, they can be trimmed back.

The best time to cut your dahlias is in the cool mornings, although you may cut at any time of day. When selecting your blooms, choose blooms that are 1/2 to 2/3 open. Cut your dahlia stems at least 12" long to help your plant. You may be taking multiple unopened buds from some varieties to get the desired stem length. Place the cut stems in 2-3" inches of very hot water, 160-180 degrees (hotter than most standard house hot water tanks, but not boiling). Put them
in a metal or plastic container (coffee can or plastic bucket) and let them remain in hot water until it has cooled, or about 1 hour. Do not use glass containers, as the water will cool too quickly. We recommend adding “cut flower” food at this point, such as Floralife. Be sure that your bloom heads are above the container edge so that the steam will not burn the flower petals. This is a one-time “hot water” treatment. This will set your blooms and help your dahlias last 4-6 days or more. After this process has been completed, the stem that was in hot water will show a slightly different color, which is just a watermark on the stem. At this point, you can cut your stems to any length you like, and they do not need to be re-treated if cut and should go in cool tap water. It is best to change your water daily in your vases and keep all leaves out of the water as they promote and create bacteria that will shorten the life of the blooms.
See videos at dahlias.com

Removing dead blooms from your plants and cutting your dahlias will help promote more blooms and stronger plants. The more you cut, the more they bloom! Please remember not all dahlias are excellent cut flowers.

Hand weeding is the only type of weed control we recommend; there are no exceptions. Do not use any type of weed killer, pre-emergent (Preen), or herbicide in or around your dahlias. If weeds do not grow there, neither will your dahlias. The only product that may be used, if absolutely necessary, is Round-Up or products on the market that are comparable. If you choose to spray with Round-Up or a similar product, do not let any spray drift onto the dahlias and foliage, as it will kill them. These products are not pre-emergent and do not stay in your soil. Double-check product labels before application.

Although not recommended, when using bark dust or mulch, be sure to apply it after the dahlias have sprouted and pushed through the ground. The product should be kept away from the base of the plants by at least 12" to allow water and nutrients to reach the tubers. Mulch soaks up the water and doesn’t allow the water to reach the roots. Please watch the pH level of your soil when wood products are applied yearly, as the level can change over time. See soil preparation in Spring Care for more details on adjusting pH levels in your soil.

Key to keeping your plants & tubers healthy

A thorough spraying program is the best method to prevent the spread of disease and viruses, as vectors (aphids, thrips, and other insects) are one of the main transporters.

We strongly recommend preventively spraying before issues arise and continue spraying throughout the season. In general, as with most plants, dahlias should be sprayed with an insecticide every two to three weeks (following the manufacturer’s recommendations) during the growing season. A good spraying program is the best preventative to stop infestations, virus transport, and create overall healthiness of your plants. Begin spraying once your plants have reached 12" or more and continue throughout the growing season and into the fall. The sprays listed here are just a few of the name brands available. Ortho, Bayer (BioAdvanced), and Monterey brands produce excellent all-around sprays. You may also check with your local garden center for other great products available in your area. When looking for a product to use on or around your dahlias, anything safe for vegetables, roses, or other flowering plants will work fabulously for your dahlias. We carry a wonderful line of products on our website or at our farm in our Pest & Disease Control section. Spraying is necessary to stay ahead of pest issues.

General Insects

Some general insects that attack dahlias are leaf miners, stem borers, aphids, and thrips. Recommended sprays: Bayer (BioAdvanced) 3 in 1, Monterey Garden Insect Spray, Orthene, Neem Oil, Sevin-5, Organocide, and Malathion. All organic sprays tend to work best for preventative care but are not as effective in treating a problem that already exists.

Snails & Slugs

Treating slugs and snails is critical during the first few weeks after planting in all areas until sprouts are through the soil. Slugs/Snails will eat the sprouts off nightly before you ever see them. Apply slug/snail bait after planting and continue applying throughout the season. Any slug or snail bait product at your local garden center will work. We recommend applying regardless of visible trails. We find many times there are no trails, as they can live up to 5' underground.

-Other Helpful links:

   -managingslugssnails.pdf (oregonstate.edu)

Earwigs

These insects will crawl up your plants and most often are found hiding or chewing on your blooms. They can be a nuisance especially when you cut your dahlias to bring the beautiful blooms inside. We recommend treating your plants with Sevin-5 dust or spray, malathion, or sprays containing pyrethrins.

Cucumber Beetles (similar to a ladybug, but green instead of red)

These insects fly in daily and are hard to control. They especially enjoy chewing on light colored blooms. We do not treat for them as we do not want to harm ladybugs and other beneficial insects. We recommend hand-picking them off your blooms.

Spider Mites

Spider Mites are the biggest and most common predators of dahlias. These pests will cause your plants to look brown around the base with possible spots on the leaves. Spider mites feed on leaves during the summer and return to the soil for the winter and must be treated for to prevent future issues. Typically, your dahlia plant will look like it needs more water. Most plants will begin with yellow spots on the leaves and then the leaves will begin browning completely, working their way up from the bottom, and eventually killing the entire plant. Spider mites thrive in hot weather and can attack certain varieties, while not bothering others right next to it. If you take a leaf off the bottom of the plant and turn it over, it could look dusty/dirty and feel grainy. These are tiny pests that are hard to see with the naked eye. These pests will appear and thrive mostly when the temperature rises and you water more, as they love humidity and hot temperatures. We recommend preventively spraying beginning 60 days after planting and continuing through the entire growing season. We recommend spraying with a Miticide, Monterey Horticultural Oil, Bayer (BioAdvanced) 3-1, Malathion (good for prevention, but does not work as well on infested plants), or any spray that lists mites in its description.

Mildew

Most commonly shows up in the fall. The leaves will begin to get a white powdery mildew or spots on the leaves. We do not believe that this is caused from overhead watering, but rather weather temperatures and humidity. We recommend preventatively spraying before this issue arises, begin spraying in late July and continue through the fall. Recommended sprays: Daconil, Funginex, or Fung-onil, or any Oil-based sprays.

Although dahlias can get different diseases, pest damage can often be resolved by taking care of the pests by spraying with an insect spray related to the plant issue. Although the virus can occur, the virus is not common and your entire crop will not suddenly all have a virus. Many insects suck the juices out of the leaves, creating crinkled leaves or lines. This is not a virus but sign of pest damage that should be treated for. Please do not dispose of any plants or tubers until we have had a chance to look at your photos and diagnosis them. Please use our Contact Us page.

Powdery Mildew (white fungus on leaves)

Powdery mildew is an air-borne spore you either have in your location or don’t. Mildew commonly shows up in the fall with damper weather conditions. The leaves will begin to get a white powdery film or spots. We do not believe this is caused by overhead watering but rather by weather temperatures and humidity. We recommend preventively spraying before this issue arises. Begin spraying 60 days after planting and continue through the fall, depending on your location. Reapplying about every 10-14 days or per the manufacturer’s directions on the spray, you are using. Recommended sprays: Daconil, Bayer (BioAdvanced) 3-1, Funginex, or Fung-onil, or any oil-based fungicide sprays. If you do not treat for powdery mildew, it will kill your plant and potentially get into the tubers, killing them as well, which is devastating.

Crown Gall

Crown gall is a disease caused by the bacterium Agrobacterium tumefaciens, which enters the plant through wounds in roots or stems and stimulates the plant tissues to grow in a disorganized way, producing swollen galls or a cauliflower-looking mass. This bacterium is found in soil. If any of your dahlias have grown gall, we recommend that they be disposed of immediately. Crown Gall can be found in woody plants, including fruits, vegetables, shrubs, and ornamental plants. We recommend removing the soil in your planting area to prevent further contamination if a gall is found. Please remember to disinfect all tools between clumps of tubers to avoid any cross-contamination. We are working to have more research done with dahlias.

Leafy Gall

Leafy gall is caused by the bacteria Rhodococcus fascians which enters the plant through wounds of the stems and roots of many herbaceous plants. Infection with this disease causes dense clusters of distorted leafy shoots that are fused together. If any of your dahlia clumps show signs of leafy gall, they should be disposed of immediately. We recommend removing the soil in your planting area to prevent further contamination if a gall is found. Please remember to disinfect all tools between clumps of tubers to avoid any cross-contamination. We are working to have more research done with dahlias.

General Insects

Preventative measures are always better than trying to get rid of pests once they arrive. Some general insects are leaf miners, stem borers, aphids, and thrips. Recommended sprays: Bayer (BioAdvanced) 3 in 1, Monterey Garden Insect Spray, Orthene, Neem Oil, Sevin-5, Organocide, and Malathion. All organics tend to work best for preventative care but are not as effective IN treating a problem that already exists.

Mosaic

Mosaic Virus in dahlias will cause large-scale disfigurement of the plant. It is found worldwide and is spread by inoculation of the sap, either through human intervention or by the 13 species of aphids that serve as its natural vectors. Dahlias with Mosaic Virus can exhibit many symptoms, such as variegated leaves, yellowing on the leaves that follow the veins, or stunted/ gnarled plants. Please treat your plant for pests and watch the new growth before assuming it is a virus.

If you suspect any issue, please send photos of the plants along with close-up photos of the bottom and top new growth on your plants. If your new growth on the top of the plant looks normal, this is a very good sign that it is just pest damage and not a virus.

In general, dahlias do not do as well in pots or containers as they do directly in the ground. If you choose to grow your dahlias in pots or containers, we recommend using the low-growing or dwarf varieties of dahlias, as they are easier to maintain. However, any variety can be grown in a raised bed or container. When choosing a container, ensure there is adequate room for tuber growth. A dahlia could be easily planted in a 15" x 15" pot. For example, you could plant 3 full-size dahlias in a “whiskey barrel” sized pot due to the volume of soil. Raised beds should be a minimum of 12" deep to allow proper growth and drainage.

The planting medium should be 2/3 garden soil/topsoil to 1/3 potting soil or all garden soil. Potting soil alone is too porous, dries out too quickly, and will cause poor growth and blooming results. Be sure that the potting soil and garden soil used are not chemically sterilized or treated with any type of weed killer or herbicide. Avoid potting soil that includes high nitrogen fertilizers, such as Miracle-Gro, compost, etc., as they will burn and rot the tubers.

The difference between growing in containers rather than on the ground is they will need water to start growing. Please make sure to keep your soil slightly damp or cool to the touch after planting, not soaking wet. After planting and until you see the sprouts above the soil level, water sparingly, about once a week. Overwatering to keep the soil wet will result in rotting tubers.

Once the dahlias have sprouted above the soil, water them daily or as often as you would any other container plants. After plants are 12" high, potted dahlias will require extra watering and fertilizing to promote proper growth and blooming. We recommend fertilizing dahlias in containers and raised beds much more often than those planted directly in the ground, as the fertilizer is washed through the soil quicker.

Dahlias need to be watered consistently for proper growth and blooming. In containers, we suggest watering them 1 to 2 times daily once your dahlias are above the ground.

Fertilize approximately every 2–3 weeks with low nitrogen fertilizer or choose a slow-release fertilizer and follow the manufacturer’s recommendations. In raised beds, you will water less often than in a container; however, more often than dahlias planted directly in the ground due to drainage. Fertilizing your dahlias in raised beds is similar to containers, applying it every 2–3 weeks.