Compost is a great way to reduce waste and improve your garden soil. However, it is important to remember a few things to prevent spreading diseases, weeds, and pests. A large, properly-maintained compost pile can reach the needed time-temperature conditions that will cook most potential pathogens and render them harmless. Unfortunately, most home compost systems do not achieve this goal.
You should think twice before adding any plant material to the compost heap if it has died from a disease. The factors that determine if it is safe to add something is how the disease survives and spreads. Some diseases cannot survive outside a living plant host while others create survival structures that allow them to remain infectious in the soil for years. A few of these long term survivalist diseases that should never go into your compost pile are downy mildew, hosta petiole rot, white mold of tomatoes, and Fusarium.
Many pests can finish their growth and reproductive cycles after they are placed in the compost pile and from there move back into your garden. Others such as nematodes can live in the compost heap and then infect the plants when the compost is placed onto the garden.
The compost pile may seem like a perfect place for recycling pesky weeds, but here again you must be careful. Some plants such as creeping Charlie and Asiatic dayflower are capable of growing new plants from chopped up remains. Plants that are flowering or producing seeds should not be added to the compost pile. Many weeds can continue to produce seed from flowers even after they have been pulled. Those seeds will then germinate happily in the compost and spread to your garden.
These examples are only the tip of the iceberg and to be safe it is best to dispose of all infected materials in the trash. Stick with things such as food scraps, leaves, and healthy plant material to create compost that improves your garden without spreading problems.
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