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What conditions should qualified seedlings have?
The quality of seedlings directly affects the survival and growth of seedlings. Choosing qualified seedlings for planting not only has high survival rate and fast growth, but also can exert greening effect as soon as possible, and has strong resistance to adverse environmental conditions. Qualified seedlings should meet the following conditions:

1. has a strong growth, a good tree skeleton foundation and well-distributed branches. The terminal buds of seedlings with axial branches should be full and free from damage. Seedlings should have a good skeleton foundation in their infancy, and only when they grow up can they have a beautiful tree shape and grow healthily.

2. The root system of seedlings is developed, with many lateral roots and a certain length, and the main roots are short and straight. Specific requirements should be based on seedling age and specifications. The older the seedlings are, the more roots they should have, which is generally determined by the height and rhizosphere diameter of the seedlings. Nanjing has made the following provisions on the requirements of general seedling roots for reference.

Requirements of root system of seedlings of various specifications

Table 8- 1 requirements for root system of seedlings of various specifications (continued)-1

For slow-growing or deep-rooted tree species, the requirements for root system should be appropriately increased.

For evergreen seedlings with soil balls, the size standard of soil balls depends on the characteristics of seedling roots and tree species.

3. The ratio of the aboveground part of the seedling to the root should be appropriate. Under the condition of the same tree species and seedling age, the seedlings with small ratio of stem to root and large weight have good quality. The so-called stem-root ratio refers to the ratio of fresh weight of stems and leaves above ground to fresh weight of roots underground. Small ratio means that the seedlings with developed roots but too small ratio of stem to root are weak due to small growth above ground, and the quality is not good.

4. The height-diameter ratio of seedlings should be suitable. The ratio of height to diameter refers to the ratio of the height of seedlings to the diameter of root neck. It reflects the relationship between seedling height and seedling thickness. The seedlings with suitable height-diameter ratio grow evenly, neither too thin nor too thick, generally100 ~ 80:1.

5. No pests and mechanical damage: The above indicators are mainly morphological indicators of seedling quality, and those that meet the requirements of the indicators are considered as qualified seedlings. When evaluating the quality of seedlings, these indexes should be considered comprehensively, and the grade should be determined according to the national or provincial standards of main garden tree seedlings.