This week 
Many people would normally feel that pressure treated wood is the way to go when building planters. They last longer, and avoid rotting with the moisture from the soil. However the chemicals use to treat this pressure treated lumber are harsh and can leach into the soil and eventually the vegetable plants. There is a bunch of ideas that the amount of leaching is so minimal that it really is not a concern, but personally I feel much better to avoid pressure treated wood all together.
Another idea would be to use Hardwoods, they will last longer than softwoods untreated but they are expensive and they will rot over the course of less than 4 years. Really not a long term option.
So what would be an ideal method to built and seal or preserve the wood for vegetable planters for the long term? I have a couple of ideas that work, and are generally accepted that are chemical free. I have attached a Youtube video that speaks to this nature of testing the soil of a raised bed using pressure treated lumber.
My first choice is a homemade conditioner to apply to my wood, made with beeswax and oil. Jojoba oil and Mineral Oil are both good choices for the mix. It is simple to mix and inexpensive. These mixture of both ingredients provide a beautiful finish that will display the natural beauty of the wood. Beeswax will protect the wood surface as it repels the water and dirt. You may also want to use it as a wood conditioner. I use it as a sealant brushed over a base finish of Milk paint, which makes it food-safe and non-toxic. The mix ratio is 4 -oz of beeswax. I use the beeswax pellets, and I use 16 oz of Mineral oil, but again you can use Jojoba oil, either or works great.
So if your asked by your honey to make planters this Spring for the vegetable garden please consider all that I have said in this post. Good luck with your projects. 16 weeks to planting season....
Image Sources:
http://serenitystumps.com/bees-wax-finish.php
