I started my tomato odyssey about 20 years ago. Since then, I've run the gamut from all hybrid plants to growing a huge number of heirlooms. I prefer the heirlooms hands down for flavor. One of the problems I met along the way was finding an appropriate groundcover to suppress weeds while allowing rain to penetrate. The liquid fertilizer applied via water mentioned below can be a foliar feed, nutrients applied in irrigation water, or just a bucket of compost tea poured in the hole next to the plant. Here are the results of my search and my current thoughts on mulches.
Dust - makes a very good ground covering mulch, It is modestly effective at retaining moisture even in high heat. If the dust mulch is renewed weekly, it is 100% effective at suppressing weeds. Rainfall passes right through a dust mulch. Fertilizers and amendments can be easily raked into the soil during weekly gardening activity. The weakness of a dust mulch is that it is relatively labor intensive because the rows have to be tilled then raked regularly. The plants must be staked or caged so the tiller can pass down the rows between the plants. This method should be first choice for anyone who has time to work in the garden on a regular basis.
Living Mulch - is any small plant used as a ground cover beneath larger and heavier feeding plants. Some common living mulches are grasses, clovers, vetches, and some kinds of peas. They are low maintenance, suppress weeds if properly used, and can even produce an edible crop in a few cases. It is very important to know the characteristics of a living mulch before planting. Some mulches might sound good but be terrible in practice. An example of this is bermuda grass. It is short and pretty and almost completely suppresses weeds. Unfortunately, it is very invasive and will suppress the crop you are trying to protect. If rainfall is low, living mulches compete with crop plants for moisture. I have used cowpeas as a mulch in a corn planting to some effect. The corn has to be planted first and has to be spaced wider than normal. A crop can be picked from the corn and another crop from the peas. This can’t be done with tomatoes because the peas get too large compared to the tomato plants. A somewhat successful living mulch in tomatoes is white clover. The clover must be kept away from the plant stems, but it can grow in the middles of the rows. You can even run a mower down the middles and let the clover leaves and stems discharge next to the tomato stems. Be warned though that clover competes very heavily for moisture!
Hay - Can be a very effective mulch if it is used every year. The hay should be in a layer at least 6 inches thick. Weeds are suppressed, moisture is retained, and rain easily penetrates to the soil beneath the hay. The single biggest flaw with hay is that it is usually loaded with noxious weed seed or even just the seed from the hay grass. This can be a big problem if it is bermuda grass hay. If you put down a new layer of hay each and every year, the weed seed don’t matter much. Try to go back to soil cultivation and the weeds will overwhelm you.
Silvered Plastic - is a very effective ground cover and is highly effective at retaining soil moisture. It is most useful in desert climates where irrigation is required to make a crop. The silvered surface reflects significants amounts of light onto the plants which increases fruit production. Fertilizing should be done pre-plant or via liquid fertilizer applied with water. This should be first choice of gardeners in arid climates.
Black Plastic covered with wood chips - is a moderately effective ground mulch. It suppresses weeds, is relatively easy to set up, and does not require regular maintenance. Flaws are that it totally blocks rain so some form of under the plastic irrigation is required. It also prevents access to the soil so fertilizing must be done pre-plant or via liquid fertilizer applied with water.
Felted Woven Fabrics - are readily available at many stores such as Walmart, Home Depot, etc. They are effective at suppressing weeds, easy to set up, and do not require regular maintenance. They can be used with a covering of wood chips or by using wire pins to hold the mesh in place. Rain passes to some extent through most of these fabrics. Flaws are that access to the soil is limited so fertilizer must be applied pre-plant or via liquid fertilizer applied with water. These fabrics usually last one or at most 2 years before degrading beyond usability. They are relatively expensive considering how often the investment has to be replaced. Cost usually runs about $.03 per square foot.
Woven Plastic Mesh - is available in a range of weights and sizes. This material is commonly available from greenhouse supply stores. It is highly effective at suppressing weeds, permits rain to pass through the weave, and is very low maintenance. While it can be used with a covering of wood chips, it is best used with wire pins to hold the mesh in place. Flaws are that soil access is limited so fertilizer must be applied pre-plant or via liquid fertilizer applied with water. This fabric commonly lasts 4 to 5 years in direct sunlight. This material is on the high side of expensive at a price of about $.07 per square foot. Given its durability, it is a better long term value than other mulches. This method should be first choice for anyone who does not have a lot of time to spend in the garden.
I really prefer the dust mulch method of growing tomatoes, but work and customers and other concerns limit my gardening time. I’m lucky some years to get plants in the ground. Because of this, I buy woven plastic mulch in rolls 15 feet by 300 ft. I roll it out across my garden and stake it down with wire pins. This is VERY IMPORTANT. When a strong wind blows, the plastic will be picked up like a sail. It may bounce up and down on top of your plants, it may be dragged off to the side of the garden. A decent breeze that catches it just right develops hundreds of pounds of pulling force! The only way to prevent this is to use lots of wire staples to hold the plastic mesh in place. The minimum is 1 staple every 6 linear feet. I put in a staple at each edge then two more staples on the 5 ft marks of the mesh. This gives 30 square feet of mesh held down by 4 staples. Once the mesh is securely anchored down, I put plants on 3 ft centers down both edges of the 15 ft wide mesh, then cut holes in the plastic so the plants are in rows 5 feet wide by 3 feet between plants. This gives each plant 15 square feet of growing space which is just about right for most indeterminate varieties. A websource for woven plastic mulch is Shawfabrics