- Habit
- The characteristic growth or general appearance of a plant.
- Hardening off
- The process of gradually exposing seedlings started indoors to outdoor conditions before transplanting.
- Hardiness
- The ability of a plant to withstand winter cold; often expressed in terms of geographic zones.
- Hardy
- A plant which can withstand prolonged exposure to temperatures at or below 45"F.
- Heading back
- Pruning off the terminal growth of a plant.
- Herb
- A plant grown for flavoring or medicinal purposes
- Herbaceous
- A plant with a non-woody stem that dies back to the ground in winter.
- Herbicide
- Any material that kills plants, generally weeds.
- Honeydew
- Sticky, sugary secretion deposited on plants by insects such as aphid and whitefly.
- Horticulture
- The cultivation of plants for ornament or food.
- Houseplants
- Plants that are grown and raised indoors in containers
- Humidity
- The amount of water vapor present in the air. Relative humidity is the percent present in the air relative to the amount that the air could contain, given the temperature.
- Humus
- Partly or wholly decomposed vegetable matter; an important constituent of garden soil.
- Hybrid
- A plant with parents which are genetically distinct. The parent plants may be different cultivars, varieties, species or genera but not different families.
- Hydroponics
- A plant with parents which are genetically distinct. The parent plants may be different cultivars, varieties, species or genera but not different families.
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