Timothy enjoys a broad native range across various regions of Europe, the Middle East, and parts of Asia. It has been introduced to continents such as North and South America, Africa, and Oceania, where it has adapted to new environments. Although timothy is sometimes thought to be invasive in certain areas, like parts of Japan, its presence may have an impact on local ecosystems, particularly where it becomes abundant.

Though timothy is not toxic, some people develop allergies to its airborne pollen or by contacting the grass. Symptoms include sneezing, itchy nose, cough, chest tightness, congestion, and puffy eyes. Those with asthma may suffer attacks and shortness of breath. Skin contact can cause rash, hives, or welts.

Native to Eurasia, timothy has been introduced worldwide as a nutritious forage grass. It can become a weed in its native range and is considered to be invasive in 16 countries, including the United States, where it is defined as invasive by five states. It spreads rapidly through disturbed areas, including abandoned fields and roadsides, and quickly depletes nutrients from the soil. Increases in temperature due to climate change may allow timothy to spread and grow more rapidly. Continuous grazing, hand-pulling, frequent mowing, and application of herbicide can reduce invasions of timothy. However, it can be difficult to control without negatively affecting native species, so the introduction of a desirable competitor can help fully control it with minimal impacts.

The best time to manage timothy is during late spring or early summer when the plant is still young and hasn't set seeds yet.