When you think of plants, one of the first things that come to mind is usually soil. Soil is an excellent substrate because it meets all of a plant’s basic needs. You may therefore be surprised to learn that plants do not need soil to survive.
Plants do not need soil if they can get their basic needs met in other ways. Plants can grow in the air, in water, or on other plants as long as they have access to nutrients, oxygen, and water. They also need support for their roots and protection from heat.
This article will look at the benefits that soil provides plants and how they can meet these needs without soil. We will discuss three categories of plants: air plants, hydroponic plants, and epiphytes.
What Does Soil Do for Plants?
Soil is often the perfect growing medium for plants because it meets their basic needs. These are:
- Nutrients: Plants need nutrients to survive, including oxygen, nitrogen, and potassium. There are nutrients in the soil, but you can supplement them with fertilizer, compost, vermicompost, manure, or cocopeat.
- Oxygen: It may seem like plants already have access to plenty of oxygen in the air. However, plants also need oxygen for their roots. Soil is lightweight and creates air pockets around the roots to maintain oxygen flow.
- Root support: Roots are the anchors for plants. A deep, broad root system gives plants the support they need to grow taller and stronger. Soil provides a base for roots to latch onto, preventing the plant from falling over.
- Water source: Water is essential to the growth of plants. Thus, the roots must have access to enough water to stay hydrated (although too much water can also cause problems with root rot). Soil absorbs water and retains it around the roots of the plant. You can also increase water retention by incorporating other lightweight substrates.
- Heat protection: We have all seen plants turn brown and wither in the heat. Plant roots are even more sensitive to heat than the leaves. They would die very quickly if exposed to sunlight and the direct air of a hot climate. Soil keeps roots cool by preventing sunlight from reaching them and holding water to cool them.
Plants That Grow in Air
Air plants are often the first image that comes to mind when thinking about plants without soil. Often kept in terrariums, air plants are a family of plants that survive independently of any other living organisms.
Nutrients and Oxygen
Unlike other plants, air plants take in nutrients and oxygen through their leaves. Being above ground gives them unlimited access to oxygen, as well as nutrients in the air, including carbon, nitrogen, and phosphorus. Although the air does not provide enough nutrients for larger plants, air plants do not need any other nutrients.
Root Support
Air plants have aerial roots or roots that do not tether to anything. Therefore, they do not require soil for root support. The roots are not crucial to the plant’s survival, and many people remove the roots to make their air plants more aesthetically pleasing.
Water Source
Without soil to retain water, air plants are entirely dependent on their environment for a consistent supply of water. When kept as houseplants, they should be misted every few days or submerged in water each week.
Heat Protection
Air plants are found in Central and South America and the Caribbean islands. These areas are near the equator, with high temperatures and lots of sunlight. Therefore, the plants are well adapted to hot climates and do not need soil to protect them.
Plants That Grow in Water
Growing plants in water is called hydroponic growing, and many plants can fall into this category. Plants such as hyacinths, lucky bamboo, and food plants like potatoes, herbs, and peppers can be grown in water.
Hydroponics is becoming more popular as a sustainable option for gardeners. Growing plants in water can use less space by growing vertically, reducing water use, and preventing nutrient depletion in the earth.
While plants such as lotuses, lily pads, and water lilies grow in water, their roots are located in the soil at the bottom of the pond, so they will not be included in this discussion.
Nutrients
Hydroponic plants take in nutrients from the water they grow in. However, these nutrients do not occur naturally in water, so you must add a nutrient mixture to your water. Plants need a wide variety of nutrients that work together to keep the plant healthy, but they require large amounts of nitrogen, potassium, and phosphorus. These nutrients come in liquid or powder form to supplement the water.
Oxygen and Water
Soil is lightweight, so it can retain water for a plant’s roots and enable the roots to access oxygen. When a plant’s roots are submerged in water, they do not get enough oxygen. Fortunately, there are several types of hydroponic systems that use different setups to give roots access to both water and oxygen.
Root Support
Hydroponic plants are supported by a grow tray, which is generally netting that the plants sit in, though other substrates can be used as well. The plants are held up by these grow trays, which create the same support as soil to keep the plant upright.
Heat Protection
The vast majority of hydroponic plants are grown indoors or in greenhouses. This allows growers to have more temperature control over their plants and limit the amount of direct sunlight they get. Water is also slow to change temperature, so it will not heat the roots much, even on a hot day. Therefore, soil is not necessary to keep the roots from drying up.
Plants That Grow on Other Plants
Epiphytes, or plants that grow on top of another plant, are another type of plants that do not require soil to live. Ivy, moss, and lichen are all epiphytes. They can all be found on trees, the most common location for epiphytes to attach to.
Unlike parasites, epiphytes do not take anything from the plant they subsist on. Instead, they are self-sufficient and only use other surfaces as a place to live.
Nutrients
Although epiphytes can obtain most nutrients from the water and air, some of their nutrients come from the environment. This includes organic debris, excess nutrients that their host plant does not absorb, and nutrients carried by animals.
Oxygen and Water
The roots of epiphytes are above ground and have easy access to oxygen. Although water may pool in the nook of a tree or crack of a rock, these plants are often located in places that cannot retain moisture. They depend on watering, rainfall, and sometimes dew to stay hydrated. For this reason, you will find many epiphytes in rainforests and damp places with high rainfall.
Root Support
The roots of epiphytes are not deep, allowing the plant to latch on firmly to the host plant without penetrating it. These plants take in nutrients and water through their leaves, so they do not need a large surface area for their roots.
Initially, epiphytes will grow their roots right into the tree or surface, but they can also travel throughout their life. Plants in the rainforest have been known to slowly travel down from the top of a tree to the ground and eventually put down roots in the soil.
Heat Protection
The entire epiphyte plant is exposed to the air. While this is good for getting oxygen and water, it leaves the plant exposed with no barrier protecting the roots.
Most epiphytes have a higher heat tolerance than the plants you might find in a backyard garden. However, their environment also reduces the threat of burnt roots. These plants live in dark, damp environments, such as forests. These locations help protect them from excessive sunlight exposure and arid conditions.
Conclusion
Plants can grow without soil if they have other methods to meet their needs. These needs are:
- Nutrients
- Oxygen
- Root Support
- Water
- Heat Protection
Plants that do not need soil can get these requirements met through air, water, and added nutrients.
