Exploring the Impact of Cardboard in Gardening
19 August 2024, written by Benedict Vanheems
Is cardboard toxic? It’s a question many gardeners ponder, given the presence of glue, ink, tape, and other materials in its production. In this article, we’ll dissect the concerns surrounding cardboard, determine whether they’re justified, and outline safe and effective ways to use cardboard in your garden.
Potential Soil Contaminants in Cardboard
Glue
Cardboard contains two types of glue:
- Vegetable-based glue: Found in corrugated cardboard, this is made from starchy crops like potatoes, rice, or tapioca. It naturally decomposes and is harmless for gardening.
- Synthetic glue: Used for joining cardboard sheets in boxes. Although not plant-based, the small amounts used are negligible. However, if you prefer a completely natural garden, you may remove these areas.
Tape and Labels
- Tape: Most tape is plastic and doesn’t degrade, so it’s crucial to remove it before using cardboard in the garden. Biodegradable tapes exist, but the strings within them can take longer to break down.
- Labels: While some labels decompose, others are treated with plastic or glue. Remove labels to avoid introducing non-degradable elements into your soil. Wetting the cardboard can make peeling easier.
Ink
Most cardboard uses soy-based ink, which is safe for soil. However, avoid glossy or colorful cardboard, as it may contain heavy metals and harmful chemicals. These materials resist decomposition and could potentially increase toxic levels in your soil.
Chemical Treatments
Plain brown cardboard is generally untreated. However, some boxes may be chemically treated to repel moisture or reduce fire risk. If you’re unsure about its safety, opt for untreated cardboard.
How to Use Cardboard Safely in the Garden
Once stripped of tape, labels, synthetic glue, and glossy surfaces, cardboard is fully degradable and beneficial for gardening. Here are three popular uses:
1. Composting Cardboard
Cardboard serves as a rich carbon source to balance nitrogen-heavy compost materials like grass clippings or spent crops. Mix cardboard with green waste in thin layers to achieve a 30:1 carbon-to-nitrogen ratio. Turn the compost occasionally to speed up decomposition.
2. Sheet Mulching
Cardboard is effective for weed suppression when used as mulch.
- Dry climates: Cardboard may take longer to decompose. Thoroughly soak it to ensure it remains pliable and starts breaking down.
- Wet climates: Cardboard decomposes faster, often within six months under mulch. Always water the cardboard well before covering it with soil or mulch to lock in moisture.
2. Sheet Mulching
Cardboard is effective for weed suppression when used as mulch.
- Dry climates: Cardboard may take longer to decompose. Thoroughly soak it to ensure it remains pliable and starts breaking down.
- Wet climates: Cardboard decomposes faster, often within six months under mulch. Always water the cardboard well before covering it with soil or mulch to lock in moisture.
3. Weed Control
Using cardboard as a base for new garden beds or raised beds is an excellent way to kill weeds without herbicides or heavy digging. It acts as a barrier that prevents weed growth while decomposing to enrich the soil. Roots can penetrate the softened cardboard as it breaks down.
Addressing Concerns
- Soil Suffocation: Cardboard may reduce oxygen penetration in compact, heavy clay soils, but the impact is minimal in most gardens.
- Termites: Cardboard may attract termites due to its cellulose content, but it’s unlikely to draw them into your garden if they’re not already present.
Conclusion
Cardboard is an affordable, sustainable resource with versatile applications in the garden. By taking simple precautions to remove synthetic elements, you can use it safely and effectively. Whether for composting, mulching, or weed control, cardboard can be a gardener’s ally.
How do you use cardboard in your garden? Share your thoughts in the comments below!