The lavender leaves don't smell as strong as they used to.
The lavender leaves are losing their fragrance.
この場合、次のような言い方ができますよ。
ーThe lavender leaves don't smell as strong as they used to.
「ラベンダーの葉っぱは以前ほど強く匂わない」＝「匂いが薄まってきた」
ーThe lavender leaves are losing their fragrance.
「ラベンダーの葉っぱは香りを失ってきている」＝「香りが薄まってきた」
ご参考まで！
カナダ 
