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1. Break open their shell: The seed coat becomes imbibed with moisture, swells up and breaks open (hopefully). Some seeds like baobabs or almonds are impervious to water and gases. This may delay or completely prevent germination. In some cases plants may need a little help from you if you wish to be successful at growing them. There are a few ways of getting through the testa (another name for the seed’s shell). Any process of breaking, scratching, or altering it through chemical, physical or thermal methods to make it permeable to water and gases is known as scarification. You may already have heard of this.
2. Activate hydrolytic enzymes: Enzymes that are necessary in order to metabolise the food reserve (starch) are activated with water’s helping hand.
3. Wash away abscisic acid: Abscisic acid is a plant hormone that is responsible for seed dormancy. Excess water helps to wash away this abscisic acid, allowing the plant to leave its dormancy stage.
4. Help with photosynthesis: Once the food reserves in the cotyledons are all used up (you can sometimes watch this happen in beans: the cotyledons shrivel up and fall off the plant), the developing embryos produces food via photosynthesis. Water is extremely important to plants, for photosynthesis and other vital functions, if you want to learn about this, we recommend you read our post on why plants need water.

You do need moisture for seed germination, but you need it in the right quantities if you want to be successful at growing seeds. The planting medium must be kept evenly moist, but never waterlogged: too little moisture and germination will not occur, too much and your seedlings will rot.