The Q&A Archives: Unidentified Objects In Potting Soil

Question: I was repotting some container plants (rosemary, hydrangea) and noticed little yellow balls packed in the soil around the plants roots. These balls were as hard as rocks. I have looked in every gardening book I have with no success as to identifying these little things. I scraped them out of the soil before I repotted the plants. Can you tell me what these "marbles" could be?

Answer: You've discovered encapsulated time-release fertilizer, probably put there by the grower or nursery where you first purchased your plants. One trade-name is Osmocote. Adding this type of fertilizer is common practice in the nursery trade. Water dissolves the outer coating and allows the fertilizer to slowly seep out.

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