Usually, yes. For many plants, slopes are not a problem. It is critical that when cultivating on steep slopes one does not contribute to soil loss or even potentially worse situations, such as landslides. As long as vegetation is currently on the slope, it is possible. Since it is often difficult to access and work on steep slopes, it depends on what plant(s) you are interested in growing and the access to the site.
A practical question will be how
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