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Reusing items that would otherwise be tossed in the recycling bin or trash, frugal gardeners sometimes repurpose paper towel and toilet paper rolls into biodegradable seed pots when starting seeds indoors, combining a love of DIY tricks and gardening know-how. While this approach is as noble as it is economical, the soil in the pots needs to stay quite moist to germinate, and wet conditions can lead to mold growth on the cardboard roll.

These makeshift pots end up soggy either because of the very high humidity conditions the seeds need to germinate, or the indoor gardener being heavy-handed with the watering can — or both. As we all know from the mildew that grows in our showers, mold thrives in wet environments. If precautions aren’t taken, a glowing seed starting setup can quickly turn into a frightful, fungal takeover. And who wants to grow fuzzy mold when they’re trying to cultivate vegetables?

Just as there are different types of fungal organisms that can damage plants in the garden, such as blight and powdery mildew, wet conditions can also encourage the growth of unwanted microorganisms on indoor seed trays. Damping off is a plant disease that can cause seedlings to fall over and perish, caused by fungal and fungal-like microorganisms. Sometimes, this disease kills seedlings before they manage to emerge from the soil.

Your seedlings are at risk of damping off if you see fuzzy growth creeping across the soil, but white mold on the outside of the pots shouldn’t be a concern. Once the young plants are transplanted into the garden, fungi will make the most of this DIY pot’s biodegradable properties and help turn it into organic matter. However, if the pot falls apart before it’s time to plant it, this reuse is — well, essentially useless.

While you may not be able to prevent your DIY toilet paper seed pot from falling apart before transplanting, there are steps you can take to avoid mold growth on repurposed cardboard tubes. Being careful not to overwater seedlings is by far the most important step indoor gardeners can take. Keep your seedlings warm rather than letting them sit in moist, cool conditions, which allows pathogens to thrive. Rather than potting soil, sow in seed starting soil, which is sterile and free from the microorganisms that cause damping off. If you want to take your gardening game up a notch, do as the professionals do, and apply a fungicide or bio-fungicide to the seeds at sowing time to help protect them from mold. When using fungicides, be sure to follow the manufacturer’s recommendations for applying the product.

In the end, you may decide that reusing cardboard rolls for this purpose is not ideal for your gardening plans. Plastic-free alternatives to these DIY gardening pots include CowPots, made from composted cow manure or soil blockers, which are both simple soil tricks for starting seeds more sustainably.