bruxupanswered grow question 3 years ago Soil with slow-release nutrients tend to last a few weeks to about a month, but there are different factors including the pot size, and the size and health of the plant itself. You will probably be good for the first few weeks as the plant sprouts, but you will likely have to add additional nutrients down the line when the plant is bigger. As the roots grow, they will most likely deplete the nutrients in the soil sooner rather than later. Hope this helps. Cheers!