This is one of my favorite fertilizers. It is safe for snails, and contains no copper.
What you need
Live plants are not high-tech and only have a few requirements: they need micro- and macro- nutrients, good lighting, and carbon dioxide. Combined, these factors can really help plants, and increase growth. However, if even just one of these factors is limited, plant growth will really be inhibited.
Micro- and Micro- Nutrients: Most of the time, fish wastes and minerals in water changes are enough to supplement the plants. However, in heavily planted tanks, or tanks with very little fish, aquatic fertilizers should be added. There are many commercial products to choose from. Look for something low in phosphate because it can cause algae blooms. Also, keep in mind that if you have snails, copper should be avoided, because it can poison and kill them.
Good Lightening: For plants to grow, they really need adequate lightening. The simple light you might get with a kit. Good lighting is at least 1 watt/gallon. Better would be 2-3 watts/gallon. Investing in a better light fixture with more bulbs is really worth the money.
Carbon Dioxide: Carbon dioxide is essential to aquatic plant growth and can be added in DIY methods to help. See the CO2 tab in order to learn more about this.