In general, most plants grow by absorbing water and nutrients from soil. Soil's nutrient content, texture, and acidity together determine whether the plant will be able to meet its life cycle needs. But soil is only important after seed germination has already occurred. Need proof? As this video demonstrates, seeds can sprout outside of soil, provided a few environmental conditions are met.
A seed is a tiny plant-in-waiting. Inside its protective coating are leaf, stem, and root parts just waiting to emerge. Germination marks the time when a plant starts to grow from a seed. The conditions that plants need for germination and growth vary among species. The most important ones are temperature, water, oxygen, and, to a differing extent, light. Seeds germinate over a wide range of temperatures. Some seeds will not germinate above or below a certain temperature. For example, seeds that grow in colder climates do not germinate until spring or early summer when the soil and air have warmed.
Germination also requires moist conditions. As seeds take in water, the swelling creates the pressure needed to crack the seed coat for germination. Once the seed coat is cracked, the germinating seedling needs oxygen for its metabolism. Moisture and oxygen levels are closely linked; if a seed gets too much moisture—as in flooded conditions—it may not get enough oxygen, and growth will not take place.
For certain plant types, light must be present in order for their seeds to germinate. Many seeds in forest settings, for example, will not germinate if sufficient light does not penetrate the canopy and reach the ground. Conversely, there are plants that need darkness in order for their seeds to germinate. Cactus and other desert plant seeds can only germinate in total darkness deep within the soil.
Once a seed has germinated and the root and shoot begin to grow, plants rely on nutrients to continue their growth. The sixteen chemical elements that are important to a plant's growth and survival are divided into two main groups: non-mineral and mineral. Non-mineral elements include hydrogen, oxygen, and carbon—nutrients found in air and water. Plants use these nutrients along with energy present in sunlight to produce their own food in a process called photosynthesis. Mineral elements come from soil. They are dissolved in water and absorbed by the plant through its roots. The primary nutrients are nitrogen, phosphorous, and potassium. When these minerals are missing from soil, farmers or gardeners wanting to grow crops or a small vegetable garden add them to the soil using natural or synthetic fertilizers.
To view another experiment designed to show how beans and seeds can germinate outside of soil, check out Germinator.
To watch time-lapse footage of plant development, from germination to flower formation, check out From Seed to Flower and Plants-in-Motion.
To learn about each step in the life cycle of a seed plant, check out Life Cycle of a Seed Plant.
To learn about plants that act as both producers and consumers in an ecosystem, check out Carnivorous Plants.