QUESTION: How soon can I plant after adding compost? I don’t want to mess up my garden.
ANSWER: Ideally, when using homemade compost, you should amend your garden soil with fresh compost in the fall ahead of the spring planting season so the compost has all winter to decompose and release its nutrients into your garden’s soil. However, as long as your compost is completely mature and ready to use, there is no danger of “burning” plants with fresh compost or otherwise harming your plants if you need to add compost and plant immediately afterward.
You can also feed existing plants with compost if they need a nutrient boost or the last batch of compost has been in the garden long enough to give up all its nutrients by using the side dressing technique. With side dressing, you add a layer of compost to the area where plants are growing, but leave some space around the plants themselves.
The reason you leave empty spots between your plants and the compost is to prevent a reaction between your plants and the microorganisms the compost is full of. In short, with the side dressing method, compost is handled just the same way you’d use mulch in the garden, and it can serve many of the same purposes.
When you side dress with compost, not only do you make its nutrients available to your plants, you also increase the soil’s capacity for water retention (especially important in the summer) and prevent weeds from growing where the compost has been spread.
Commercial compost purchased from a nursery or garden center does not need to be laid out in the garden in fall; it can be added in the spring when you plant for the season, because store bought compost is less likely to need additional time to decompose completely so it is fully mature and ready to use.
Instead, store bought compost is fully mature at the time of purchase, so its nutrients will be accessible to plants immediately once it is added to your garden beds. The exception is commercially manufactured compost that includes an abundance of fibrous material or is thick due to containing lots of green matter. This type of commercial compost should be added to garden beds in fall for a spring planting, just like homemade compost.