Chloe Zhang
Plastic containers are a popular choice for gardeners due to their durability, lightweight nature, flexibility, and strength. They are also readily available, easy to move, maintain, and replace. However, with increasing concerns about the safety of plastics and their potential to leach chemicals, many gardeners are unsure about using plastic containers for their seedlings. The type of plastic used is crucial, as some types of plastic may leach harmful chemicals into the soil when exposed to heat and light. Understanding the safety of different plastics and taking precautions, such as using food-grade plastic, monitoring temperature and humidity, and choosing light-coloured containers, can help ensure healthy seedling growth without the risk of chemical leaching.
| Characteristics | Values |
|---|---|
| Advantages | Durability, lightweight, flexibility, and strength |
| Safety | No evidence that plants can uptake BPA and BPS, but theoretically possible that leafy greens could be affected by leaching |
| Plastic type | Use food-grade plastic, avoid RIC 3, 6, and 7 |
| Plastic colour | Opt for light-coloured containers to avoid direct sunlight |
| Potting medium | Use a medium with a high amount of organic material to act as a filtering system for chemicals |
| Seedling propagator | DIY seedling propagators from recycled plastic containers are an excellent, sustainable, and versatile way to grow seedlings |
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What You'll Learn
Pros and cons of plastic containers
Plastic containers are a popular choice for gardeners due to their durability, lightweight nature, flexibility, and strength. They are also readily available, affordable, and can be recycled. However, there are concerns about the potential health risks associated with using plastic containers for growing plants.
Pros of Plastic Containers:
- Durability, lightweight, flexibility, and strength: Plastic containers are durable, lightweight, flexible, and strong, making them easy to move, maintain, and replace.
- Moisture retention: Plastic containers are excellent for moisture-loving plants as they help retain moisture.
- Affordability and accessibility: Plastic containers are readily available and often inexpensive or free, such as recycling empty buckets from grocery stores.
- Recyclability: Using recycled plastic containers for seedlings is sustainable and environmentally friendly.
- Customizability: Plastic containers can be customized to meet the needs of different plants, such as adding electrical heating or stacking them for upward growth.
Cons of Plastic Containers:
- Chemical leaching: The potential for chemical leaching from plastic into the soil and plants is a significant concern. While there is no solid evidence, it is theoretically possible for plants to absorb chemicals, especially if they rest directly against the plastic. Certain types of plastic, such as RIC 3, 6, and 7, are known to leach harmful chemicals when exposed to heat and light.
- Health concerns: Due to health concerns, some gardeners prefer alternative materials like wood, metal, bricks, or stone for planting.
- Sunlight sensitivity: Plastic containers, especially dark-colored ones, can degrade quickly when exposed to intense sunlight, leading to breakage.
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Safety concerns and chemical leaching
When considering whether to plant seedlings in plastic containers, one of the primary safety concerns is chemical leaching. This process involves the potential migration of harmful chemicals from the plastic into the soil and, subsequently, into the plants themselves.
The type of plastic used for containers is crucial in understanding the risks associated with chemical leaching. Different types of plastics are identified by a resin identification code, which is usually stamped on the container. For example, polypropylene (PP) plastics are commonly used for plant pots and are generally considered safe, as they are resistant to leaching. On the other hand, polyvinyl chloride (PVC) plastics are more likely to leach harmful chemicals, such as phthalates, which can be toxic to both plants and humans.
Another factor to consider is the age and quality of the plastic containers. Older plastics may degrade over time, increasing the likelihood of chemical leaching. Additionally, low-quality or recycled plastics may contain impurities or contaminants that can leach into the soil. It is important to source plastic containers from reputable suppliers who adhere to safety standards and regulations.
To minimise the risks associated with chemical leaching, it is recommended to choose containers made from safer materials, such as clay or terracotta pots. However, if plastic containers are the preferred option, it is advisable to look for containers made from safer types of plastics, such as polypropylene or polyethylene (PE). Additionally, using a barrier, such as a fabric liner or a thick layer of mulch, between the plastic and the soil can help reduce direct contact and minimise the potential for chemical leaching.
It is also important to note that certain plants may be more susceptible to the effects of chemical leaching than others. Plants with shallow root systems or those that are particularly sensitive to their environment may be at higher risk of absorbing harmful chemicals. When planting seedlings, it is advisable to choose containers that are appropriately sized and made from materials that will not compromise the health of the plant.
Overall, while plastic containers can be convenient and affordable options for planting seedlings, it is crucial to consider the potential safety concerns associated with chemical leaching. By selecting the right type of plastic, ensuring the quality and integrity of the containers, and taking appropriate precautions, gardeners can minimise the risks and create a safer environment for their plants to thrive.
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Choosing the right plastic
Plastic containers are a popular choice for gardeners due to their durability, lightweight nature, flexibility, and strength. They are also inexpensive and widely available. However, there are concerns about the safety of using plastic containers for plants, especially food crops. Some types of plastic are known to leach chemicals into the soil, which can be absorbed by plants and ingested by humans. Therefore, it is essential to choose the right type of plastic to ensure the safety of your plants and yourself.
When choosing plastic containers for your seedlings, opt for food-safe plastics such as high-density polyethylene (HDPE), marked with a 2 inside a triangle on the container. HDPE is very safe and is not known to transmit chemicals into the soil or food. It is commonly used for concrete mixing trays and is excellent for blending soil mixes. Another option is low-density polyethylene (LDPE), marked with a 4. LDPE is very flexible and is commonly used for garden hoses and semi-flexible plastic pots. Like HDPE, it is not known to leach chemicals into the soil, making it a safe choice for your garden.
Polypropylene, marked with a 5, is another food-safe plastic that can be used for your seedlings. It is commonly used for products that require injection moulding, such as straws, bottle caps, and food containers. While it may not be as heat-tolerant as HDPE or LDPE, it is generally safe for use with food and in the garden.
If you want to be extra cautious, you can opt for plastic containers made from polylactic acid (PLA). PLA is a biodegradable plastic often used for food packaging. It is considered safe for both the environment and human health. However, PLA containers may be more expensive and less durable than other plastic options.
When using plastic containers for your seedlings, ensure they have adequate drainage holes to prevent water buildup, which can harm your plants. Also, keep your plastic containers out of intense sunlight, and when possible, opt for light-coloured containers to reduce the risk of chemical leaching.
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DIY seedling propagators
A propagator is like a mini incubator, usually made of plastic, that provides young, vulnerable seedlings with a warm, constant environment. It helps get seed germination underway more efficiently, giving gardeners a head start on the gardening season.
You can purchase propagators, but it is also possible to make your own DIY seedling propagator using recycled household items.
Materials
You can use recycled fruit and vegetable trays and soda cans to make a DIY seedling propagator. You will need two fruit or vegetable punnets, one to act as a transparent cover and the other as an opaque growing tray. You will also need a drip tray for the growing tray to sit in.
Other items that can be used to make seedling trays include yoghurt pots, which are easy to pierce drainage holes in, and butter containers, which can be used as water trays.
Plants
You can start plants such as tomatoes, courgettes, and chillies in seedling propagators. You can also advance the growing season of plants that are typically sown outdoors, such as peas and beans, by at least one month by starting them indoors in a propagator.
Tips
- Make sure to add drainage holes to your seedling trays to prevent root rot.
- Use "seedling compost" to fill your trays, but note that you don't need to fill the entire tray with it.
- Water your seedlings well, but be careful not to overwater and cause your drip tray to overflow.
- Before planting your seedlings outside, you will need to harden them off, as they will have become accustomed to the heat and protection in your propagator. Move them to a cooler, protected place, such as a greenhouse or small polytunnel, about six weeks before you plan to transfer them outdoors.
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Alternatives to plastic containers
There are several alternatives to plastic containers for planting seedlings. Here are some options:
Ceramic and Terra Cotta Pots
Terra cotta (or terracotta) is a type of ceramic clay that is porous, allowing plants to breathe and promoting healthy root development. Modern terra cotta pots are often frost-proof, durable, and long-lasting. However, they can be more expensive than plastic options and may require careful handling due to their weight and potential for breakage. When purchasing ceramic pots, look for those that are labelled "food safe" to avoid lead-based paints.
Fabric Containers
Fabric containers, such as canvas bags or grow bags, are lightweight and flexible alternatives to plastic. They are made from a variety of materials, including wool, recycled milk bottles, and natural fibres. Some fabric containers, like the "grassroots living soil pots," have a BPA-free plastic lining to prevent water seepage. While fabric containers can be prone to mould if overwatered, they offer good drainage and airflow for plants.
Wooden Seed Trays
Wooden seed trays are a traditional and plastic-free alternative for starting seedlings. They are typically the same size as standard plastic seed trays but may be slightly deeper and heavier. Wooden trays provide a large surface area for scattering seeds and can be used in conjunction with biodegradable egg cartons or cardboard boxes for modular planting.
Newspaper Pots
Newspaper pots are a cheap and plastic-free option for starting seedlings. They can be easily crafted at home by folding and rolling newspaper sheets, providing a biodegradable and space-efficient solution for gardeners.
Food-Grade Buckets
Food-grade buckets, such as those used by bakeries for icing and batter, can be sourced for free or at a low cost. These buckets are typically made of food-safe plastic and can be cleaned and reused for planting. However, they may become brittle and break after several years of outdoor use.
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Frequently asked questions
Plastic containers are generally safe for seedlings, but it's important to monitor the type of plastic used. Some plastics may leach harmful chemicals into the soil when exposed to heat and light, so it's best to avoid plastic with RIC 3, 6, and 7 for edible crops. Additionally, keep plastic containers out of intense sunlight and opt for light-coloured containers to prevent rapid degradation.
Plastic containers are lightweight, durable, flexible, and easy to maintain and replace. They are excellent choices for moisture-loving plants and can be easily transported. Plastic containers are also versatile and can be customised to meet the needs of your seedlings.
If you're concerned about using plastic, there are other options available. You can use traditional clay and ceramic containers, recycle glass or paper containers, or opt for fabric containers like Smart Pots, which are fibre-based and lightweight.
