"has grown lower" is correct and usable in written English.
You can use it to describe something that has declined in amount or intensity. For example, "The number of applicants for the position has grown lower since last year."
The cost of moving water long distances has grown, while lower costs of technology and other factors have made these smaller, decentralized projects less costly.
Investor appetite has grown, also lowering the cost of capital.
For three consecutive months, from March through May, industrial production in South Korea has grown at a lower rate than the month before.
Although the D.C. budget has grown, revenue is lower than expected, in part because of a cooling economy and the 35-day partial shutdown of the federal government, which hurt retail, hotels, restaurants and other businesses across the city.
Since 2001, employment has grown 8.7 percent in lower-wage occupations and 6.6 percent in high-wage ones.
But the difference in interest rates, or spread, between the top-rated commerical paper and that issued by companies with lower ratings has grown because of concerns about potential credit problems among smaller, riskier issuers.
"In a Mellow Tone," in particular, showed that Ms. Callaway, who has always been so good at fluty sound effects that she has underused her middle and lower registers, has grown more comfortable propelling phrases from deep inside her body.
Sleep America carries lower margins has grown substantially in recent periods due to an agreement to place Sleep Number mattresses in Radisson Hotels over the next several years.
And in the six years hence, the middle class has shrunk significantly, the lower class has grown dramatically, and the wealthiest 1percentt has run off with 95percentt of income growth.
Our knowledge about mechanosensation in lower organisms has grown rapidly, but many exciting questions remain open for mammalian systems (Chalfie, 2009).
