“Slow Release” has become a marketing gimmick for fertilizer sellers. They will all try to tell you that there product is “slow release” because in most consumers minds this adds value. So they splash it all over on the front of the bag. To really get the real truth, you should look carefully at the analysis label on the bag. The truth lies within this labels information. It will always disclose what percentage of the nitrogen contained therein is slow release. The cheap fertilizers will say 20% or less of the nitrogen is slow release, but the more expensive types will say 50% or more is slow release. The reason they are more expensive, is that they have to create some type of coating or mechanism around the fertilizer particles to slow down the distribution of the nitrogen. We don’t want that, we want the cheap stuff for our purposes. If the nitrogen isn’t soluble it will not be available to the bacteria and this will make the conditioning process happen more slowly. Look for the least expensive bag of fertilizer, then double check the analysis tag and make sure it has 20% or less slow release nitrogen, or 80% or more soluble nitrogen. Whatever amount of phosphorus or potassium is included doesn’t really matter much, as most of it will simply wash out, until we begin to build up soil particles in the bale. At that point, usually day 10 in the recipe, the Phosphorus and Potassium will have something to bind with as it makes its way into the heart of the bale.
I like to use Ammonium nitrate or ammonium sulfate, but these are usually sold at the farmers coop, or farmers elevator and they come in a plain brown bag. It is likely you won’t find these for sale at your garden center, but you could ask. Otherwise, just go to the cheap lawn fertilizer section. Do not use any fertilizer that contains herbicide. Do not buy weed and feed. Do not buy fertilizer with preemergent crab-grass-preventor. Just buy plain old fertilizer, usually a store brand works great.
Dry straw would provide a lovely home for a mouse or nest for a snake, but once the straw is saturated with water and begins to break down and heat up inside the bales, the bale is not at all hospitable to a mouse or snake. If you woke up in a hotel and the roof was leaking on your head every morning you would check out quickly, and that is how a mouse feels too. If they are trying to nest, they need a dry spot to protect their baby mice. If you let your bales dry out, or water very infrequently so they have a chance to dry up in spots, then a mouse might appear, but my experience has been that if I water regularly, they are not a problem. Snakes are not attracted to straw, however if they already live in the area of your garden, they may take the opportunity to sun themselves on top of the bales before the bales are covered with plants to shade the surface. Snakes are usually very beneficial in a garden, as they eat slugs and other pesky insects that can be the real trouble makers in a garden. I sure wish I had snakes in my garden. You will not find any more snakes in a Straw Bale Garden than you will find in a traditional garden in the same exact spot.
If you know you already have gophers, chipmunks, moles or voles, one great option is to unroll a long run of 3′ wide chicken wire, or hardware cloth, then arrange your bales right down the middle of the wire, bending it up on the sides. This little wire “trough” will keep most of them from trying to tunnel into your bales from underneath. If you have shrews, those suckers are tiny, so use two overlapped chicken wire fences with the holes off center. This usually does the trick. Hardware cloth wire is effective but it can be expensive, actually more expensive than two rolls of chicken wire.
If you find straw bales in the fall and you plan to store them over winter, do not keep them inside of your garage or potting shed. The will serve as a mouse hotel if you do. Instead put them outside, right in the garden where you will use them. Store them so the string don’t touch the soil, and don’t bother covering them up, the snow or rain will help soak them and start some bacteria build up. The real conditioning will only start when you add the nitrogen source.
You will discover that all of your concerns about rodents are usually overblown, and the damage they inflict is minimal at most. So stop worrying about what you think is going to happen, and just start a garden. Let the results speak for themselves, you’ll see your fears were mostly unwarranted.