You try it first and let me know.

Wow. Maybe we should trade plants - I'd LOVE an 8 foot dahlia. The workhorse dahlia in my yard was store bought, gets the MOST sun in my yard and grows about 5 1/2 ft of foliage. (I can be eye to eye with a few of the blooms and I am 6'2). The vast majority of mine seem to be 3-4 feet. I have never even SEEN a dahlia that was 6-8 feet high and I go to the SF Dahlia Garden every year as well.

It may be whatever fertilizer you are using. I once closely inspected the many fert. choices at Home Depot and was surprised to learn that the "0-10-10" numbers not only applied to the ingredient percentages but that the first number was meaningful to plant growth, the 2nd was bloom size and the 3rd was applicable to whatever. (Don't hold me to which is which however - I'm paraphrasing.) All I remember is ferts. with a certain specific number said 'promotes bloom quality/quantity'. I thought they ALL promoted plant growth AND bloom production but apparently you can have one over another by choosing the right fert.

I think Ted's your man when it comes to fertilizers. He knows more about that than I'll ever learn.

David

Dahlias grow taller in part shade. People who grow them under shade cloth report that a variety that may reach 5 feet in full sun will grow to about 8 or 9 feet tall under shade cloth. Many people have dahlias reach to 10 feet under shade cloth.

So, I am assuming that you have a bit of shade in your garden and dahlias are reaching for the sun.

Fertilizer in so far as what the ratios of N-P-K are used has little to do with plant height. Dahlias need fertilizer that is balanced, meaning that some of each number is present. Since phosphorus, the middle number is being banned in some states, it may be difficult to find a balanced fertilizer. However, most gardens accumulate phosphorus and if you fertilized in past years, there will be enough in the soil.

I use fertilizer that is high in both Nitrogen and Potassium. The ratio is 4-1-4 and the actual numbers are 20-5-21. I mix my own fertilizer and buy three fertilizers to achieve that number. This is very concentrated fertilizer and a little goes a long way.

Whatever fertilizer you use, apply in small amounts very frequently and the plants will do better. People tend to over fertilize and that is not good for the environment.

My dahlias are all southern facing and get blasted with sun from morning till 5:00 PM and they all need to be staked or they fall over. Most are >4' or as much as 5.5' tall, producing at least 3-5 stalks. I wish I could get them to be a little lower.

DahliaDahlias plants very tall what can i do?

Is it to late to pinch the top?