What is Mulching?
Garden Mulch is a layer of material applied on the top of your soil. Mulch maintains a more constant soil temperature, provides nutrients for your plants, and keeps your soil moist throughout the summer. Mulching will also reduce weed germination and the amount of water needed for the plants. (There’s a reason soil is always covered with natural mulches in nature.)
Mulching Tips
- Best applied in the spring and in late fall to keep the soil warm
- It can slow soil warming if applied too early in the spring
- Do not till the mulch into your garden soil before planting in the spring because the decomposition will tie up nitrogen that plants need to grow.
- Mulch is best applied to your beds after transplants have been placed in the soil and direct-seeded crops have emerged and grown partway to maturity.
- To prevent weeds, lay a thicker layer of mulch to prevent weed emergence
Types of Mulch to Use
We suggest the following mulch options, with the best options listed first:
Grass Clippings
Apply a 1-2 inch layer of clippings around the base of plants. Green clippings are rich in nitrogen, which is slowly released to the plants. It is very important to use organic clippings that aren’t contaminated with herbicides or synthetic fertilizers from the yard.
Straw (Not Hay!)
Apply a 1-2 inch layer underneath your maturing vegetable plants. You can leave straw mulch in place at the end of the growing season to protect the soil through the winter. Be sure the straw is “weed and seed free”, otherwise you’ll have a number of surprise crops in your garden the next year. Hay is fantastic, but sometimes it has grass seeds in it if it was harvested late in the season, making it undesirable in many instances. While both hay and straw can make great mulch, especially if they are certified weed-free by the Colorado Department of Agriculture, straw is the safer bet. However, straw isn’t as good as green grass clippings, because it doesn’t have as much nitrogen in it (green materials are high in nitrogen, while brown materials are high in carbon).
Compost
Apply a 1-2 inch layer of low-salt compost around the base of maturing crops. Backyard compost is by far the best quality compost you can use. After applying a thin layer of compost, consider covering it with another type of mulch so the compost will stay moist and biologically active. Mulch like grass clippings and compost releases nutrients into the soil and creates high biological activity at the surface of the soil.
Black and Colored Plastic
Many commercial growers use black or colored plastic to mulch their warm season crops. It’s great for heat-loving vegetables such as tomatoes, peppers, and eggplants, as well as for vine crops (cucumbers, summer and winter squash, pumpkins, watermelons, and cantaloupes). Plastic warms the soil allowing for earlier crop growth—typically 2-3 weeks earlier production with higher yields—but dark plastic is too hot for all cold season crops. You can use white plastic mulch to keep the soil cool for cool season crops like kale, cauliflower, and broccoli. Plastic also retains soil water incredibly well, but doesn’t allow rainwater to permeate. Therefore, use drip irrigation with plastic mulch. To use plastic, lay the plastic over the entire bed, and hold down the edges with pins or rocks. Cover edges completely with soil to keep tight. Punch holes in the plastic for the plants, and transplant seedlings into the holes. Do not use black mulch under shrubs and trees. If you use plastic mulch, save the plastic every year for re-use.
Mulch Not to Use
Wood Chips. Large pieces of organic matter such as wood chips tie up nitrogen in your soil during decomposition. The woodchips also tend to get in the way in future years. Peat moss used as mulch tends to dry up and blow away. It does not hold water very well, and adds no nutrients to the soil. It is also significantly more expensive than other mulch options. Manure (depending on the type) tends to be high in salts, so The Urban Farm Company does not suggest adding very much of it to your vegetable garden every year.
Our recommendation is to mix organic green grass clippings with shredded leaves. Shredding leaves can be difficult, but there is a great tool that can make the process easy.
Shred for the soil! Here’s a link to the magic tool.
Hay is NOT “straw with seeds in it”! Hay is grown as forage for livestock; straw is the leftover stems of a crop such as wheat, oats, barley etc from which the seeds have been harvested. Hay is usually leafy like grass, and yes, sometimes it does have grass seeds in it if it was harvested late. Both hay and straw can make great mulch, especially if they are certified weed-free by the Colorado Department of Agriculture.
Thank you for the info and the correction, Suzanne!
Where can I buy weed and seed free straw in the Denver area?