Dahlias require full sun (at least 6 hours daily) to thrive and bloom abundantly. Southern growers might need to provide plants with afternoon shade if summer temperatures are extreme. Dahlias are cold sensitive and should not be planted until the soil has warmed to above 60°F (15°C) and all danger of frost has passed. Check with your local county extension office to find out the date of your last spring frost.
Select a sunny garden spot with freely draining soil and prepare it thoroughly before planting. Amend beds with 2 to 3 in (5 to 10 cm) of high-quality compost or well-rotted manure, a light dusting of bonemeal, and a balanced organic fertilizer. Mix all ingredients into the soil to distribute evenly.
To plant, dig a hole 4 to 6 in (10 to 15 cm) deep and place the tuber on its side, horizontally, with the growing eye facing up. Refill the hole with soil. Dahlias get quite large, so allow at least 12 in (30 cm) of space between plants.
Dahlias require consistent water throughout the growing season, so install soaker hoses or drip irrigation while they are still young. Dahlias should not be watered until you see the first green shoots poking through the ground; overwatering before shoots are visible can lead to tuber rot. After plants reach 8 to 12 in (20 to 30 cm) tall, give them a hard pinch by snipping out 3 to 4 in (7 to 10 cm) of the growing center to encourage low basal branching, which increases flower production and overall stem length.
Slugs and snails damage young plants, and earwigs ruin the flowers. Put down bait at planting time and periodically throughout the season. Sluggo Plus is an organic option that’s safe for both children and pets and works well against all three pests.
By midsummer, you’ll need to stake tall plants to keep them from falling over. For home gardeners with just a few plants, place tall, sturdy posts next to tubers at planting time so you can tie stems to them as they grow. For flower farmers, I recommend the corral method, which involves placing a metal T-post every 10 ft (2.4 m) along the outside edges of the beds and stringing a double layer of bailing twine from post to post.
While dahlias are not terribly long-lasting cut flowers, you can get 5 to 7 days from stems cut at the proper stage. Since dahlias don't open much after they’ve been harvested, it’s important to pick them almost fully open, but not overly ripe. Check the back of each flower head, looking for firm and lush petals; papery or slightly dehydrated petals are a sign of age. Be sure to use floral preservative in the water.
July 29 2024
Dahlias need warm, well-drained soil. Your dahlias will do best when planted in your existing soil, if it has not been treated with Preen, Casoron, or other herbicides. If you have heavier soil, we recommend amending it with peat moss to help lighten it up. Do not amend dahlia beds with purchased topsoil or potting mix unless you are sure that it has not been treated for weeds or enhanced with fertilizer. Too rich of soil can burn your dahlia sprouts and cause them not to grow at all. Even if you think you do not have the best soil, this soil may be better than bringing in new soil.
To increase the nutrients in your soil, the best all-around soil additive is cow/steer manure. If you choose to add compost to your dahlia beds, please do so sparingly, as we do not recommend it. Most types of compost are high in Nitrogen, which promotes tall spindly plants, small blooms, less blooms, and tubers that are weak in storage.
If you are planting a new dahlia bed, make sure to check all soil, potting soil, and materials being used carefully. The soil must not be sterilized or contain any type of weed killers (herbicides), compost, or fertilizers. If weeds won’t grow in the soil, neither will your dahlias. Although many herbicides (Preen), on the market state they are safe for dahlias, we disagree as we have seen negative results. Hand weeding is the only option when growing dahlias. The pH level of the soil should be 6.5-7.0, slightly acidic. To adjust the pH level in your soil you may add Lime to increase your pH level, or Sulfur to decrease your pH level. Please check with your local garden center or extension office for recommendations for dosage and application.
Dahlias need a sunny location to thrive! More sun equals more blooms. It is recommended that dahlias receive at least 6-8 hours of sunlight per day. Do not plant your dahlias under trees or too close to shrubs as they will not receive enough sunlight or nutrients to thrive. They can be grown with less sun, but please remember that less sun means less blooms and taller plants, reaching for the sun. Of all dahlias to consider growing with less sun, the lower growing and dwarf dahlias will do the best. In hot climates (such as Texas, Arizona, Southern California, many other southern U.S. states, or desert climates) morning sun with some afternoon shade may be best for proper growth. We recommend not growing bi-color varieties in hot climates, as the white tips can burn. Please remember dahlias require deep water 3 times a week or more by a sprinkler or soaker hose for at least 45–60 minutes during the growing season to bloom properly.
Dahlias are ready to go in the ground when your ground temperature has reached 60 degrees or warmer. Be sure that your soil is workable and not soggy. The ground should be warm, well-drained at planting, and in an open sunny location.
If you have heavier soil, add sand, peat moss, or bagged steer or cow manure to lighten and loosen the soil texture for better drainage. Planting dahlias too early, in cold wet soil, may result in rotting tubers. Dig a hole 4-6” deep, lay the tuber horizontally (on its side), then cover it completely with soil. If the tuber sprout(s) is longer than 2 or 3" in length, it would be best to trim/pinch the sprout back to a length of 1”. This will not hurt your dahlias, in fact, this will help them have a stronger stalk by pushing through the soil. We recommend planting 12-24" apart. An average 4' dahlia plant will be 18"+ in diameter.
Bone meal is ideal at planting time. Add a small handful of bone meal to the hole and work it in well before planting the tuber. However, beware if you have pets or other animals around, they are attracted to bone meal and may dig up your tubers, we would recommend skipping this step.
This is the ideal time to put in your garden stakes. AT THIS POINT YOUR DAHLIAS DO NOT NEED MUCH WATER UNLESS YOU ARE GROWING IN CONTAINERS (See container growing instructions). Begin your watering regimen AFTER sprouts have appeared above the ground. There is an EXCEPTION in hot climates and/or container growing, where you will need to be sure the soil is slightly damp at planting as tubers do need a small amount of moisture to get growing. In hot climates, we recommend light watering once a week after planting until the sprout appears. Naturally, we assume Mother Nature will give us enough rain in the northern states at planting time, that additional water is not needed until you see the sprouts above ground. However, with changing climates, if your dahlias are planted in bone dry conditions and you aren’t receiving any rain for a few weeks, you will need to provide your dahlias with a little moisture to get started.
At this point do not cover your dahlia beds with bark dust or any other mulch as this will prevent the ground from warming up and allowing your dahlias to get growing. Snail and slug bait should be applied immediately in all climates.
Continue applying slug and snail bait throughout the season to protect them. The average time for dahlias to sprout through the ground is 3-5 weeks. If you have any dahlias purchased from us this season, that have failed to sprout through the ground after 5 weeks, dig them up and contact us immediately for assistance. Do not discard them, as photos of them will be required or return of the tubers may be requested.
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, please visit our website or farm to view options available.
Many areas receive enough rain to fulfill water requirements for dahlias until the sprouts appear above the ground. Do not water your dahlia tubers after planting unless your ground is dry and no rain is expected in the next few weeks. If, however, you are planting in a hot and dry climate, you will need to water once a week to help the tuber establish its root system until the sprout appears above ground. If you are growing in containers, please see container growing instructions for recommendations.
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 not sufficient for dahlias and will not allow the water to get deep enough to their roots.
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. Please see the diagram or video on our website dahlias.com for additional information. We recommend continuing to dead head your old flowers all season long. If at any point your dahlias are too tall, they can be trimmed back.
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 will 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, be sure to 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 prior to 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.
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, the second is commercial fertilizer. We recommend using a combination of both. Steer manure can be worked in prior to planting or applied on top of the soil of your established flower beds. Commercial fertilizers can be applied starting 30 days after planting and throughout the growing season. Dahlias require low nitrogen fertilizer. We recommend using a fertilizer with a higher percentage of potassium and phosphorus. A good rule of thumb is looking 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 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 fertilize. 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.
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 staying away from Miracle-Gro products as most are too high in nitrogen.
The first application of fertilizer 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 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. The 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.