How much fertilizer

dahlia1972

I’m about to plant with osmocote. How much do I use per plant?

calico20hill

dahlia1972 I used to plant with osmocote and then when I had my soil tested found out that I had toxic levels of some of the nutrients. The nitrogen gets used up or washes out with the winter rains but the others do build up. I might use it with a new bed for a year or two but get the soil tested as soon as possible then add what is recommended by a good soil test. I plant my dahlias just with a handful of alfalfa pellets for quick nitrogen after adding the recommended elements to my soil.

Krista

I’ve also always just added a handful of alfalfa pellets into the hole with each tuber, but this year I’m considering working chicken feather meal into the planting space. I wonder if the alfalfa pellets would still be ok to use for fast-food right away or if that will be overkill.

Teddahlia

Osmocote in small amounts will not build up in the soil(Ted says this and Noni and I differ in our opinions on this) . A teaspoon is a small amount. Osmocote is the rolls royce of fertilizers as the wax coated pellets release a balanced amount of fertilizer over a couple of months. Alfalfa is excellent too and has an NPK of something like 3-1-2 and you would need about 5 times as much to match the osmocote. The Waltons used both in the holes. Alfalfa is a slow release too but not like osmocote that has even release. In our hanging baskets where we use potting soil, the osmocote is critical for fertilizing the plants. I do not like to mix up greenhouse fertilizer outside and osmocote works well. Max Ollieu is master show person and his soil has lots of the P and the K from his addition of wood ashes to his dahlia beds. He uses a time release N product only as his fertilizer. Such fertilizers are harder to find, however. At the trial garden in Swan Island we use alfalfa in the holes and chicken feather meal has been applied to the whole bed. It is a slow release organic nitrogen product. Fertilizer and dahlias is a complex, long winded and controversial subject. Ph was not mentioned at all and micro nutrients not mentioned. We could go on and on.

calico20hill

Ted, I based the statement about it building up in the soil on my own experience from official soil tests done by WSU extension services. THis was when I lived on Vashon Island in Washington state. This was after multiple years of planting with the same mix of osmocote plus a bit of bloodmeal. I think it was before I started using alfalfa meal with it. The flower beds were not machine cultivated after the first year. Perhaps the difference is that you do cultivate more deeply with your tractor and equipment.

dahlia1972

So is a teaspoon of osmocote the appropriate amount to mix into the hole at planting? I'm trying to keep things as simple as possible- I'm not looking to buy multiple fertilizers and amendments.

Teddahlia

The addition of phosphorus is not needed in my garden, your garden and probably in most gardens where anybody has added fertilizer over the years. 19-6-12 is one of the formulas for osmocote and it would be very good. I am too cheap to actually use osmocote on my dahlias or even in the container plants. I use Haifa Multicote: Polymer-coated controlled-release fertilizer Multicote (4) 15-7-15+2MgO + Micronutrients . I have said you probably cannot find it as it is a horticultural product sold at my horticultural supply store. I think I paid about $75.00 for 50 pounds this year. This is the first time I have gotten a bit different formula that is lower in phosphorus and has some magnesium. Haifa has micronutrients in the pellets and Osmocote no longer adds them. Micronutrients are important in containers. Again fertilizer can take up more words than most subjects. By the way, fertilizer for dahlias in the ground is a very different subject than fertilizer for container plants grown in potting soil. I have to add some phosphorus to the container plants. The dahlias get plenty from the accumulation of the element in the soil.

Teddahlia

So is a teaspoon of osmocote the appropriate amount to mix into the hole at planting? Probably, but it will not be enough to keep the plant fertilized past about 4 to 6 weeks. We eat some food every day. Plants need access to fertilizer as they grow. Fertilizer (nitrogen) washes out of the soil. The dahlias will need more nitrogen during the growing season.

calico20hill

Since I shop at t he same store as Ted does for my fertilizers I hope I remember to look into their version of osmocote next year. I do use some for everything I plant out here, including a small amount in the dahlia patch. My heavy clay soil seems to have a lot of iron and not a lot of other things naturally. So I use osmocote in all my spring planted veggies and flowers. Of course they all get alfalfa pellets too.

cmcramer

Watching the big white flakes, but planning my dahlia gardens....
I decided to up my fertilizer game in 2024 so I just purchased a sack of Osmocote - Bloom with micronutrients, NPK 12-7-18, 2 to 3 month release. The manufacturer suggested application rates refer to "top dressing" and "container size", so I am trying to adapt those recommendations for my one year old Dahlia beds.
By using their "2 gallon container" recommendation as a starting point, and their Medium level application rates, I get about 18 grams of Osmocote, which turns out to be a heaping Tablespoon. So I'm thinking about one full Tablespoon - once - in early June here in Upstate NY. If I were to use the Manufacturer's 'Low' or 'High' application rate, that one heaping Tablespoon could be as little as half a Tablespoon, up to two full Tablespoons per "2 gallon container."

But, of course, I don't have two gallon containers. Any Osmocote I add has to cover a volume of soil quite a bit greater than 2 gallons!

Any thoughts about my estimate of one Tablespoon - once? Should I go for two Tablespoons, once, in mid-June? Something about adding 2 to 3 month time release fertilizer in mid-July bothers me: late nitrogen, late growth, weaker tuber for storage, so I have read. Thanks for any input!

Teddahlia

Osmocote - Bloom with micronutrients, NPK 12-7-18, 2 to 3 month release. Sounds like a "Rolls Royce" fertilizer. I have noticed that time release is good for about 6 weeks and then declines thereafter meaning you need to add some more to make up for the decline in the release of fertilizer. I have read in a fertilizer companies' literature(not time release) that phosphorus and potassium for the entire year can be applied once in the beginning of the year along with some nitrogen. Then the only thing the plants need is nitrogen in a few applications later on. With time release you are giving them all three elements all the time but as I said, it declines after about 6 weeks and a supplemental dose is needed and that would take you out to 12 weeks that should cover the growing season. Fertilizer is very complicated and one always has to do a soil test as you very well may have plenty of phosphorus in your garden and too much is not good. Too much nitrogen and too much potassium are not much of an issue. And pH is important too as plants need proper pH to absorb nutrients. One old timer I know just adds more fertilizer to make up for his overly acid soil in his garden. It works for awhile until the soil gets so acid that it will no longer work. If you let that happen, you cannot add enough lime in one year (or even in some cases two years) as there is a limit on how much lime you can add in one year.
Seedling picture.

SteveM

I agree with Ted. A good soil test does not cost much more than the price of a couple iof tubers. The formulation NPK 12-7-18 would work great in my soil but I would add some additional Nitrogen. Maybe a small hand-full of alfalfa pellets with 1 tablespoon of Osmocote mixed into each planting hole at planting time. A good soil test lab will make recommendations on what to add. Since nitrogen leeches with rain, a soil test should be done just before planting to get accurate results.

calico20hill

THat is just about what I do, Steve. We do the soil test after the New Year, and then try to get the presribed supplements on the bed shortly before planting. The Nitrogen ..probably some feather meal or something recommended but always supplemented with some alfalfa worked in under the tubers when I plant it. IN my small garden of raised beds it is hard to figure out all the other recommended elements but the clerk at the supplements store is always willing to help if you present your test results to them. I just find it hard to spread a half cup of supplements over a 4' by 20' bed! Adding a bit of Osmocote and the alfalfa under the tuber at least makes ME feel better.

Teddahlia

I will always remember the fertilizer session at the Federation where about 10 growers, most of whom had decades of experience, described how they fertilized their dahlias. Most were not organic growers but at least a couple were half and half and a couple full blown organic. Most everybody seemed to add something to the hole where they planted the dahlia tuber. Alfalfa was not yet popular nor was chicken feather meal but seaweed and chicken manure were common ingredients. One of the most experienced and successful show growers described adding a long list of items from inorganic fertilizers, bat guano, blood meal, seaweed, and who knows what to his holes and then made the statement, "and just in case I add a teaspoon of Osmocote."

And I was surprised that the most successful show grower used inorganic fertilizer in probably smaller quantities than most of us but observed her plants for health and added more according to how they looked. Everything she does to grow her dahlias is based on observation and experience and just doing most everything we do except meticulously better. I left the training session with the realization that fertilizing dahlias is not the secret potion to success but just one of many things you do correctly.
Dahlia growing over 6 feet tall in a pot. Fertilizer was Haifa Multicoat 14-14-16, a product similar to Osmocote. This picture was taken on August 5th. On about August 30th the plant, grown in a 20 gallon pot, was too tall and a wind gust blew the 8 foot plant over and it laid there for a few days and then was righted and it never looked quite as good thereafter.

calico20hill

That was a beautiful flower. Knowing its fate now, I want to retro-actively run out and take cuttings of it to root!

Cosey

I use that same brand in my fields. Based on my soil tests I use the medium application rate. I grow in 50' rows. I measure out how much is needed to cover the square footage of the 50'x20" dirt row. Sprinkle on before I plant. They act of planting I corporates it into the soil. I sometimes add a top dressing to plants that look like they need it 10-12 weeks later.

cmcramer

Sure appreciate all the experienced information and practices!