For best long-term results, dig them into the soil early in the season. They usually have higher levels of nutrients and a larger percentage of soluble nitrogen than natural fertilizers. However, when fertilizer is applied too heavily and followed with excess irrigation or rainfall, the soluble nitrogen can run off the soil and pollute surface water as well as groundwater. You can buy natural and chemical fertilizers in liquid or solid form. But, because the nutrients usually last only a couple of weeks in soil, liquid fertilizers need to be applied more often.
Liquids are useful for feeding plants in containers and hanging baskets.
They can be broadcast or spread over lawns and ground covers, or dug or raked into soil around the root zones of trees, shrubs, and perennials. To avoid burning plants, water soil thoroughly after application. Other solids include controlled-release fertilizers. Since they release nitrogen slowly and steadily, most of it is used by the plant and very little leaches out with irrigation water. Pound fertilizer spikes into the soil around trees and shrubs.