Answer: Fertilizer would provide nutrients to the plants. Fertilizer should be applied on the basis of soil test results indicating how much is needed. But, in general, for lilies you could use a general purpose granular fertilizer or a slow release granular fertilizer such as 10-10-10. Read and follow the label directions for how much to use.
Herbicides are used to kill weeds. Pre-emergent herbicide will usually stop most annual weeds such as crab grass. For this purpose you could use corn gluten. (It will also provide a bit of nitrogen for the lilies.) Read and follow all of the label directions. Perennial weeds can be carefully dug out root and all, or spot treated with an herbicide containing glyphosate. Be very careful not to allow this to contact your lily plants as it will damage or kill them.
An overall weed control approach is to keep your plants mulched year round. Use a three inch layer of organic mulch over the root area (do not allow it to touch the stems.) This will hold down weeds, help keep the soil more evenly moist, and also breaks down slowly over time to help feed the soil. The mulch will actually help fertilize as well as prevent weeds.
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