First, read the English article below.

By holding off until your roses have neared their full size, you can ensure that they’ll be able to withstand having whole sections removed. A mature knockout rose should be about 4 feet (1.2 m) tall by 4 feet (1.2 m) wide before you begin hacking at it.  A fully-grown knockout rose will require the most pruning around mid-February to early March. Young roses, by contrast, only need to be touched up throughout the growing period to remove dead or dying growth.  Knockout roses can often go as long as 2-3 years between major prunings, depending on how rapidly they grow and how big or small you like to keep your plant. Look for small buds to begin forming along the stems of the plant. If the existing buds have swelled up but no new growth has appeared, it means the roses are ready to prune.  The main pruning period for knockout roses is in late winter or early spring, just as the plant prepares for another season of growth.  You can still prune your roses even if new growth has already begun. Buds might start forming early if the winter was especially mild. In this case, snip the growth back to the first dormant bud. Clip one or both canes as needed to get the plant’s interior structure growing straight and vertical. Creating some separation between the canes prevents them from rubbing against one other, making the plant look neater and promoting stronger, more lasting growth.  By reducing the density of your rose bushes early in the season, you can make sure they continue putting out neat, attractive growth all year long. Thinning out overlapping canes and stems also promotes better air circulation through your rose bushes, making them less vulnerable to fungal diseases. You can cut healthy shoots back considerably without worrying about harming the plant. Doing so will prevent your roses from putting too much energy into maintaining an overabundance of foliage. As a result, it will produce more flowers.  Keep in mind that your knockout roses will grow vigorously after being pruned. As a general rule, you’ll... 

Now, please write a short abstract for it in Vietnamese. Abstract:
Đợi đến mùa sinh trưởng thứ hai hoặc thứ ba của cây. Tỉa cây ngay khi các chồi nhú ra sau thời kỳ ngủ đông. Bắt đầu bằng cách cắt bỏ các cành cây mọc chồng lấn nhau. Cắt bỏ một phần ba hoặc một nửa tổng số cành cây của bụi hoa. Tỉa bớt cây đến chiều cao và rộng mà bạn mong muốn.