It is a good idea to mulch your garden no matter what you are growing. With tomatoes it is a requirement. Tomato plants need to be mulched to moderate the soil temperature, to control weeds and to retain the moisture around the base of the plant. Another important reason for mulching is to prevent a disease called ‘early blight.’ This disease is caused by soil splashing up onto the foliage during watering. The leaves at the bottom of the plant will turn yellow with dark spots on them, and start spreading up the plant, and to others close by. The best prevention for this is to mulch between the time you plant your tomato seedling and the time you water it in for the first time.
Mulches also keep the sunlight from getting to weed seeds in your red mulch and at least cutting down on weeds. Weeds can provide a living space for various insects and pests that carry diseases with them that are harmful to your tomato plants. Organic mulches you can use on your tomato garden are things like grass clippings that have not been treated with an herbicide, wheat straw, hay, pine straw and chopped leaves. You can place newspaper pages down as a base and put other organic mulches on top of that. The newspaper will eventually break down and you can work it into the soil.
Clear plastic will not work because in order for the soil to heat up enough to choke out weeds, the tomato roots will be cooked. Red plastic is supposed to make the tomato plants more productive because the sunlight is reflected back up to the undersides of the leaves. It gives them double the power of the sun.
It is said that no area of your garden should be left unmulched. Whether it is the beds or the pathways, you should cover everything. It cuts down weeds, retains moisture, and cuts down on muddy shoes when you walk back into the house.