One of the most difficult orthograms in Russian is an unstressed alternating vowel at the root. For example, the words "plants", "growth", "grown" and "grown" have the same root but are spelled differently. What determines the choice of "a" or "o" in the roots "rast", "rasch" and "ros"?
Spelling type
Unstressed root vowels are of three types: checked, unchecked and alternating.
When faced with an unstressed checked vowel in the root, it is enough to choose a test word in which this letter will be stressed. For unchecked, such words are not selected, so the correct spelling can only be learned. The alternating cases are especially important to remember, as trying to define a vowel using cognates can lead to an incorrect result.
The spelling in the roots "growth", "growth" and "growth" belongs to this type.
Rule
The correct vowel can be chosen based on the type of root: the letter "a" is written before "st" and "u", and "o" is placed before "c": germinate, overgrow, grow, grow, overgrowth, sprouted.
Naturally, in the roots "rast" and "ros" under stress, you need to write the vowel that is heard, as, for example, in the word "growth".
Exceptions
In the case of the root "rasch", the rule is always fulfilled, and there are exceptions for the roots "rast" and "ros".
In a few words with the root "growth", always written "o": sprout, usurer, Rostov, Rostislav, for growth. All words formed from data are also written with "o".
For example, "usury" is formed from "usurer" with the suffix "est", so the root vowel is "o". The noun "sprout" was obtained by adding the suffix "ek" to "sprout", therefore, in this case we write "o".
The exception with the root "race" is the word "industry" and all its derivatives. For example, the adjective "interbranch", formed by the prefix-suffix method.
Thus, for the correct choice of a vowel in the roots "rast" and "ros" it is enough just to remember a simple rule and exception words.
