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, 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

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.

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 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.

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. 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.