It is very good, and I would recommend a three to six inch layer when you first put it down, depending on the size of your plants. It will settle some.
Bill P.

I've had this question myself. Thanks for posting it!

My tomato plants are only about eight inches high. I put about 1-2 inches of straw down. Should I add more straw as the plants grow?

And what about strawberry plants? They don't really get that tall, would I really use 3-6 inches of straw mulch?

I'm new at this, previously I had done mostly container gardening. Thanks for any help!

Straw is fantastic. There can be an issue where there are straw are seeds which might sprout but they're usually very easy to pull and add to your compost pile. It's good to know your source so you know what you're getting

Hay and Straw Glossary

A popular organic mulch, hay is commonly used to protect soil and plants from the elements, to line pathways, and to address various needs in the garden. What many people don�t realize, however, is that various products are often labeled as "hay" at garden centers, but there are many different types of hay and straw that are commonly sold in bales. While they are easily confused, it�s important for gardeners to become familiar with the differences.

Salt hay
Salt hay, or Spartina patens, is a grassy plant that grows in salt marshes and wetlands. Martha has long used salt hay in her gardens. It is useful for keeping weeds from growing in paths, preventing runoff, and keeping soil from turning into mud whenever it rains or the garden is watered. A layer of salt hay will keep soil moist and encourage worms to come to the surface, which will help to aerate the soil. It also makes an attractive path to walk on between garden rows. Salt hay is an ideal all-purpose mulch because its seeds won�t grow away from salt water�so it won�t germinate in your garden.

Golden straw
What is commonly termed "Golden straw" is either oat straw, Avena, or wheat straw, Triticum. This straw is a by-product of the process of separating oat or wheat seeds from their stalks. Golden straw is often used as bedding in horse stalls; because there are no seeds, the horses won�t eat it. This straw spreads nicely, and the lack of seeds means there is no risk of it germinating in your garden. It can be used in the same way as salt hay.

Wheat straw
An excellent choice for straw for use in the vegetable garden. Lay down six inches in height in the fall then direct sow seeds in the spring. No need to dig. There will be a handful of weak sprouts from seeds, just pull them out.

Feed hay
Just as its name implies, feed hay is used to feed livestock. Though inexpensive and plentiful, it is not a good choice for use in gardens because it is full of seeds. The main ingredient of feed hay is alfalfa, Medicago sativa. It also frequently contains flowers and seeds from many other plants and weeds such as clover and golden rod. These seeds are likely to germinate, resulting in a garden full of weeds rather than flowers and vegetables.

I use it for everything, too. At least an inch to start off and then I add more as I see it is needed. I also use grass clippings later in the season as they become very available from a neighbor, so I end up with a layered mix of grass clippings and straw which continuously breaks down. Straw is nice and dry as a mulch and the light color seems to repel some insects by reflecting sunlight upward to the undersides of leaves.

How you apply the straw will have a huge influence over the thickness. If you shake the straw apart to fluff it you will need a thicker layer than if you just lay the unshaked slices around plants.

Some friends who invested in an expensive round bale chopper use it to chop and blow the fine chopped straw around their sprawling tomato plants. A few inches of the finer straw is adequate.

Let your eyes be the judge of straw quality. Weed seeds are more influenced by the farm that the straw came from than the cereal grain type. I've seen wheat (typically less weeds)fields loaded with seeding thistle and oats (shorter stubble and often more weeds) that has hardly any weed seeds). Look for uniformity of material.. thicker weed stems and leaves or obvious weed seeds on the bale surface are an indication that you need to avoid that source of straw.

Assuming that you will purchase the straw bales invidually rather than by weight, look for longer, heavier (35-40 lb) bales to get a better bargain. The slices of the bales should break apart easily and not be moldy for ease of spreading although for mulch purposes you might look to get a good deal on moldy (baled wet) straw.

I still prefer hay over straw because of the superior nutrient content. A well cared for (few weeds)field of alfalfa that was rained on near to time it was to be initially baled is an excellent mulch and often available at less than $1 per bale. Rather than shaking the moldy hay apart just lay the bale slices around your plants.