Re-posting what to do to UP the scent: slow-released fertilizer & use a moisture retentive medium like potting soil or dense clay. Magnesium is what makes soil sticky and it also retains nutrients to help with scent. Potting soil (with peatmoss & lime) has plenty of magnesium and is a denser medium than sand.
https://www.houzz.com/discussions/5957059/ph-of-soil-can-affect-fragrance
Sylvia: Lavender Crush's scent is strong in Walmart's pot (late fall with rain), and strong in my always-wet alkaline clay (fertilized with chicken manure which is high in boron, zinc, and copper ... these trace elements are added to chicken-feed).
Potassium is MOST AVAILABLE when soil is wet, so hot & dry weather would lessen scent. Among my 130 fragrant own-root roses, the lavender & purple roses' scent are best with tons of acidic rain, but ABSENT during hot & dry.
Berrypie: Agree .. it took 2 years before the scent of Christopher Marlowe become strong. In its 1st year, I was disappointed in its mild scent, now Christopher Marlowe is 10th-year own root, and I love its strong scent.
Katy: If you google potassium co-factor, you'll see magnesium. Potassium works best when there's magnesium. Magnesium is what makes clay soil sticky. Magnesium makes soil dense thus retains nutrients. My clay is tested exceedingly high in magnesium at pH 7.7, and nearby Cantigny rose park is also alkaline clay but fluffier than mine.
The roses at Cantigny park are SUPER-FRAGRANT .. even the "mild" scent Lilian Austin is very strong. But the SAME ROSES have zero scent at Chicago Botanical Garden which is LOAMY & SANDY with less sticky magnesium to hold potassium & trace elements.
LEACHING is a big problem with loamy soil. I detected ZERO SCENT at CBG's old garden roses, and even their Gertrude Jekyll had zero scent after week-long rain.
However, my Eglantyne and Lilian Austin as own-roots can't compare to the heavenly scent at Cantigny. Why? Potassium is most available when soil is WET with some magnesium for density, such as potting soil (peatmoss is actually dense, rather than fast-draining like sand). Pots are well-fertilized with NPK 20-20-20 plus trace elements. My clay is very high in magnesium to the point of rock-hard, thus limit potassium mobility, but the scents improve when I make my soil fluffy.
Magnesium is found in sticky & dense organic matter such as alfalfa meal, any leaves, also high in rocks and pea-gravel, and Azomite. I tested Azomite for cut blooms, and Azomite stuck tight to the bottom of the vase .. I had to scrub it with a brush. My high magnesium clay sticks tight to my skin. Soap and water won't take it off, I have to scrub my skin with alcohol to get the clay off.
That's why topping with leaves, dolomitic lime (has both calcium and magnesium), pea-gravel or Azomite helps to retain scent plus UP the pH of rain in acidic & high-rain region.
https://www.houzz.com/discussions/5957059/ph-of-soil-can-affect-fragrance
Q
Helpful post from strawchicago
Q