When setting up a naturalistic terrarium for a frog, plants are always a wonderful - and for some speicies - a necessary addition. Live plants or artificial plants can both be used, and there are precautions to take with both.
With live plants, one consideration is whether the plant itself is compatible and appropriate for the living conditons required by your frog. Plants, just as frogs, require certain conditions to thrive in so it is important that your frog's ideal environment matches the plant's ideal conditions. You also need to take into consideration the size and weight of the frog in comparison to the size, sturdiness and hardiness of the plant. You can also match plants from a frog's natural geographical habitat if you wish.
Here is a helpful
plant page with images for determining which plant is best for your terrarium:
Once you have chosen the non-toxic and environment appropriate plants you wish to have and purchase them, there are precautions that need to be taken before adding them to your frog's tank. They need to be removed from the soil they came in and washed thoroughly, roots and all. They then need to be replanted in a safe soil - free of any fertilizers, pesticides or any other chemicals and allowed to grow for 6 weeks before being added to the tank. This allows the pesticides/fertilizers and any other chemicals which have been absorbed into the stalks and stems of the plants to "grow out" of the plant. Otherwise, these toxins can be absorbed from the plant by the frog and are potentially fatal.
Here are some additional plant pointers:
With artificial plants, you need to be sure when selecting them that the stalks and stems are plastic covered, not exposing any wire or containing any sharp points. They should be washed thoroughly to remove any dust, dirt or other potentially harmful substances as well as to be sure there are no dyes which will run/bleed. If they run or bleed under running water, the dye can be absorbed through a frog's skin as well which is potentially fatal to the frog. You should also choose appropriate size and sturdiness for the imparticualr species of frog. Some of the cheaper made artificial plants - with plastic only stems and no leaf support - will work great for a small tree frog to support it's weight but would not hold a larger tree frog, but the more expensive ones with wrapped wire stems and leaf supports will.
Different plastic plants have different textures. Some are plastic with very slick and smooth leaves and others are fabric which are more rough. Some frogs have preferences and dislikes when it comes to texture, so if your frog avoids a plant, you could try a different type.