Repurpose the shell after you finished your candle.
To do so, use a hair dryer or a heat gun to melt the remaining wax and to remove remaining wick and the metal sustainer.
Once you have removed the majority of the wax, use hot water to scrub the shell with a sponge to remove the remaining wax.
After cleaning the shell, you can use it to store many things including, jewellery, keys, pens, any general items and you can even plant some kitchen plants inside. Do not use as a bowl to store food or drink, as it is not safe for that.
The time between your order and the actual tree planting will vary depending the time of year. Planting usually happens during the rainy season, when the soil provides optimum conditions for tree survival.