A Season-Long Look at Five Mulches: What Worked, What Didn’t
Getting Started
This garden trial set out to compare five common mulch options—black plastic, landscape fabric, pine needles, shredded wood, and plain cardboard—against bare ground. The goal was simple: see how each one handles weeds, heat, moisture, and overall plant performance through a full growing season. The beds were planted in late April, with the same plants in each. The weather didn’t make things easy. Weeks of heavy spring rain were followed by a long stretch of summer heat, giving every mulch type a real test.
How Weather Shaped the Results
Right after planting, almost daily rainfall created soggy conditions that made it difficult for young plants and seeds to grow. Beds in lower areas lost the most plants to soggy conditions. It was so wet we could not even walk in the garden for most of the month of May. By mid-summer, the pattern flipped, and the garden went weeks without rain. Because the beds were irrigated, drought wasn’t as much of a problem as the early flooding, but the extreme heat still influenced how each mulch performed.
A Closer Look at Each Mulch
Plastic Mulches
Black plastic and landscape fabric did a good job blocking weeds, but both trapped heat. During the hottest part of summer, the soil beneath them reached temperatures well above what most vegetables are comfortable with. Flowers still grew well, but peppers, beans, and tomatoes struggled during the peak heat. A distinct downside of the plastic mulches is having to dispose of or store the mulch after the season.
Organic Mulches
Pine needles and shredded wood kept the soil noticeably cooler. They let a few weeds slip through – especially later in the season as they thinned out – but overall maintenance stayed manageable. These mulches can be tilled into the soil at the end of the growing season where they will provide additional nutrients to next year’s plants.
Cardboard
Cardboard blocked weeds almost completely, kept the soil cooler than any other option, allowed water to move through slowly, and began to break down on its own. Plants in cardboard beds tended to handle the summer heat better, especially late in the season. Like other organic mulches, cardboard can be tilled into the soil at the end of the year.
How Mulch Influenced Soil Temperature
Soil temperature plays a big role in how vegetables grow, especially during summer heat. When soil temperatures rise too high, root systems and plants become stressed. Warm season vegetables like tomatoes, peppers, squash, melons, etc. prefer a soil temperature between 65-75°F. During a 96°F, partly-cloudy day, each bed was checked at two depths to see how much each mulch blocked or trapped the heat. The numbers show big differences among the materials.
Soil Temperature by Mulch Type
Mulch Type 1" Depth (°F) 4" Depth (°F)
Bare Soil (Control) 99 90
Shredded Wood 94 86
Pine Needles 91 86
Cardboard 88 82
Landscape Fabric 106 91
Black Plastic 122 103
Cardboard and the two organic mulches kept the soil far cooler than the plastics. Black plastic, in particular, pushed temperatures well above what warm-season vegetables typically tolerate.
How Much Weeding Each Mulch Required
Many gardeners care just as much about weed pressure as they do about plant growth. Over the 175-day season, each 9' × 8' bed was weeded as needed, and the total time was tracked. The differences were significant.
Total Weeding Time Over 175 Days
Mulch Type Total Weeding Time
Black Plastic 30 minutes
Cardboard 34 minutes
Landscape Fabric 47 minutes
Shredded Wood 74 minutes
Pine Needles 112 minutes
Bare Soil (Control) 565 minutes
Cardboard stayed nearly as weed-free as black plastic, but without raising soil temperatures. The bare soil bed required more than nine hours of weeding—double the rest of the sections combined.
Other Notes from the Season
So Which Mulch Came Out On Top?
Looking at plant health, weed control, soil temperature, and ease of cleanup, cardboard was a near ideal mulch. It kept the soil cool, blocked nearly all weeds, and broke down into the soil without extra work. For gardeners who want low maintenance without risking heat-stressed plants, cardboard stood out as the most practical choice. Covering cardboard with a layer of pine needles or shredded wood can improve appearance while keeping all the benefits.
Related Videos:
Why to Use (and Love) Mulch!
Planting Through Sheet Mulch
Planting with Organic Mulches: A Step-by-Step Guide
Planting Cut Flowers in Different Mulch Types
Pulling Mulch Around Vegetable Seedlings
Which Mulch Is Best? 6 Week Report
Which Mulch is Best? 16 Week Report
Related Resources:
Types and Uses of Mulch in the Landscape
Mulching Your Trees and Landscapes
Mulch - A Survey of Available Options
Gardening with Mulches
This garden trial set out to compare five common mulch options—black plastic, landscape fabric, pine needles, shredded wood, and plain cardboard—against bare ground. The goal was simple: see how each one handles weeds, heat, moisture, and overall plant performance through a full growing season. The beds were planted in late April, with the same plants in each. The weather didn’t make things easy. Weeks of heavy spring rain were followed by a long stretch of summer heat, giving every mulch type a real test.
How Weather Shaped the Results
Right after planting, almost daily rainfall created soggy conditions that made it difficult for young plants and seeds to grow. Beds in lower areas lost the most plants to soggy conditions. It was so wet we could not even walk in the garden for most of the month of May. By mid-summer, the pattern flipped, and the garden went weeks without rain. Because the beds were irrigated, drought wasn’t as much of a problem as the early flooding, but the extreme heat still influenced how each mulch performed.
A Closer Look at Each Mulch
Plastic Mulches
Black plastic and landscape fabric did a good job blocking weeds, but both trapped heat. During the hottest part of summer, the soil beneath them reached temperatures well above what most vegetables are comfortable with. Flowers still grew well, but peppers, beans, and tomatoes struggled during the peak heat. A distinct downside of the plastic mulches is having to dispose of or store the mulch after the season.
Organic Mulches
Pine needles and shredded wood kept the soil noticeably cooler. They let a few weeds slip through – especially later in the season as they thinned out – but overall maintenance stayed manageable. These mulches can be tilled into the soil at the end of the growing season where they will provide additional nutrients to next year’s plants.
Cardboard
Cardboard blocked weeds almost completely, kept the soil cooler than any other option, allowed water to move through slowly, and began to break down on its own. Plants in cardboard beds tended to handle the summer heat better, especially late in the season. Like other organic mulches, cardboard can be tilled into the soil at the end of the year.
How Mulch Influenced Soil Temperature
Soil temperature plays a big role in how vegetables grow, especially during summer heat. When soil temperatures rise too high, root systems and plants become stressed. Warm season vegetables like tomatoes, peppers, squash, melons, etc. prefer a soil temperature between 65-75°F. During a 96°F, partly-cloudy day, each bed was checked at two depths to see how much each mulch blocked or trapped the heat. The numbers show big differences among the materials.
Soil Temperature by Mulch Type
Mulch Type 1" Depth (°F) 4" Depth (°F)
Bare Soil (Control) 99 90
Shredded Wood 94 86
Pine Needles 91 86
Cardboard 88 82
Landscape Fabric 106 91
Black Plastic 122 103
Cardboard and the two organic mulches kept the soil far cooler than the plastics. Black plastic, in particular, pushed temperatures well above what warm-season vegetables typically tolerate.
How Much Weeding Each Mulch Required
Many gardeners care just as much about weed pressure as they do about plant growth. Over the 175-day season, each 9' × 8' bed was weeded as needed, and the total time was tracked. The differences were significant.
Total Weeding Time Over 175 Days
Mulch Type Total Weeding Time
Black Plastic 30 minutes
Cardboard 34 minutes
Landscape Fabric 47 minutes
Shredded Wood 74 minutes
Pine Needles 112 minutes
Bare Soil (Control) 565 minutes
Cardboard stayed nearly as weed-free as black plastic, but without raising soil temperatures. The bare soil bed required more than nine hours of weeding—double the rest of the sections combined.
Other Notes from the Season
- The plastic mulches likely reduced earthworm activity. Earthworms die at sustained temperatures over 95°F.
- Organic mulches thinned through the growing season as they decomposed and settled into the ground. They might need a mid-summer refreshing to preserve their weed-blocking abilities.
- Organic mulches and cardboard began breaking down naturally, so there’s no need to remove them at the end of the year.
So Which Mulch Came Out On Top?
Looking at plant health, weed control, soil temperature, and ease of cleanup, cardboard was a near ideal mulch. It kept the soil cool, blocked nearly all weeds, and broke down into the soil without extra work. For gardeners who want low maintenance without risking heat-stressed plants, cardboard stood out as the most practical choice. Covering cardboard with a layer of pine needles or shredded wood can improve appearance while keeping all the benefits.
Related Videos:
Why to Use (and Love) Mulch!
Planting Through Sheet Mulch
Planting with Organic Mulches: A Step-by-Step Guide
Planting Cut Flowers in Different Mulch Types
Pulling Mulch Around Vegetable Seedlings
Which Mulch Is Best? 6 Week Report
Which Mulch is Best? 16 Week Report
Related Resources:
Types and Uses of Mulch in the Landscape
Mulching Your Trees and Landscapes
Mulch - A Survey of Available Options
Gardening with Mulches