The antonyms for the phrase "most high growing" can be low, descending, retreating, decreasing, or declining. When we talk about things that are "high growing," we usually mean something that is growing upwards, tall, or reaching new heights. However, when we use antonyms, we refer to things that are either staying low, decreasing in height or growth, or moving downwards. For example, a plant that was once "most high growing" may now be in decline due to a lack of nutrients or health issues. In summary, antonyms for "most high growing" are words that denote a lack of growth, or a decrease in height, size or quality.