Certain types of flowering shrubs, like rhododendron and azalea plants, require fairly acidic soil to grow properly. These plants are often native to areas with a high amount of rainfall, like the Pacific Northwest region of the United States (frequent rainfall generally lowers soil pH). For these types of shrubs, a pH range of about 4.5 - 5.5 is optimal. However, pH levels as high as 6.0 are usually acceptable. Many brightly-colored flowers, like petunias and begonias, grow best in acidic soils. For some of these flowers, changing a soil acidity from slightly acidic to very acidic can produce a visible change in the bloom color. For instance, growing a hydrangea in soil with a pH level of about 6.0 - 6.2 will produce a plant with pink flowers, while lowering the pH  level to about 5.2 - 5.5 will produce a plant with purple/blue flowers. The blue color of low-pH hydrangeas comes from the chemical aluminum. When the pH of the soil is low, it's easier for the hydrangea to absorb aluminum from the soil, which shows in the flower petals. Many needled evergreen trees grow in slightly acidic soil. For instance, spruces, firs, and pines all thrive in soils with a pH level of about 5.5 - 6.0. In addition, the needles of these types of trees can be introduced to neutral or alkaline soil as organic matter which lowers soil pH as the needles decay. Perhaps the most well-known acid-loving plant is the blueberry, which thrives in highly acidic soils (generally about 4.0 - 5.0 is ideal). However, several other species of berry also favor acidic soil. For instance, cranberries grow best at a level of about 4.2 - 5.0, while gooseberries, currants, and elderberries grow best at a level of about 5.5 - 6.5. Most varieties of garden ferns prefer soil pH levels below 7.0 — even those that prefer alkaline soils can usually tolerate slightly acidic soils. For instance, Maidenhair Ferns prefer soil pHs of about 7.0 - 8.0 but can grow even in soils with levels of about 6.0. Some ferns can even tolerate soils with a pH as low as 4.0....

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Write a summary of the previous text in Vietnamese:
Giảm độ pH trong đất cho các cây bụi như đỗ quyên. Giảm độ pH cho các loài hoa như thu hải đường và cẩm tú cầu. Giảm độ pH trong đất cho các cây thường xanh. Giảm độ pH trong đất cho một số loài cây quả mọng. Giảm độ pH xuống dưới độ trung tính một chút cho cây dương xỉ. Tham khảo các nguồn hướng dẫn làm vườn để có danh sách đầy đủ các loài cây ưa axit.