• facebook
  • twitter
  • YouTube
  • RSS feed
  • 651-201-6000
  • 800-967-2474
  • 711 TTY

NodeFire Save Document
Home > Protecting Our Lands & Waters > Sustainable Agriculture > The Greenbook > Greenbook 2017 > Evaluating Different Depths and Types of Mulches in Blueberry Production

Evaluating Different Depths and Types of Mulches in Blueberry Production

Principal Investigator: Kathy Connell, Redfern Gardens
Keywords: blueberries, mulch, soil health, weeds

Project Summary

Key Details

Project Description


Management Tips


Project Location

Other Resources

Project Summary

We examined two aspects of blueberry production while utilizing organic growing techniques. One aspect was the optimum depth of woodchip mulch and the other was a comparison of how woodchip mulch, chick litter mulch, and grass clipping mulch performed. We evaluated soil moisture retention, pH, fertility, temperature, and biological activity of the soil beneath the mulch.

We want to find ways to decrease and possibly eliminate herbicide usage, eliminate or reduce chemical nitrogen application, decrease wind and water erosion, and decrease water runoff. These will all benefit the environment. We believe it is important for the future that we maximize our farm and local resources in order to strengthen the sustainability of our farms. In addition, we believe we must share our experiences in order to strengthen our communities

Back to top

Key Details

Principal Investigator

Kathy Connell
Redfern Gardens
18298 270th St, Sebeka MN 56477
Wadena County

Project Duration

2014 to 2016

Award Amount


Back to top

Project Description

Kathy Connell owns and operates Redfern Gardens, a small farm near Sebeka where she grows fruits and vegetables. For her demonstration project, Kathy planted blueberries using four different mulch treatments and compared to plant growth, moisture, soil effects, and weed pressure across them. While the winter of ’14-15 killed more than half of her test plants, she was still able to make interesting observations about the mulch systems she tested.

Back to top

2014 Results

We prepared the planting area, which took longer than we thought because of perennial weeds. We fertilized with blood meal, and planted six blueberry plants per bed.

There were four mulch treatments:

  1. Wood shavings + a small amount of baby chick manure
  2. Grass clippings
  3. 3” wood chips
  4. 6” wood chips

The plants did not do well after the first couple of weeks. Their coloring indicated the soil was not as acidic as we thought it would be. When we soil tested, we were surprised to find pHes of 6.8-7. We really don’t understand how this happened and obviously should have checked the pH earlier. (Our original pH on this land was 5.5 and the area used has not had lime applied.) We had to acidify the area quickly in order to assure the survival of the plants, so we pulled back the mulch and applied iron sulphate to the soil, which is approved for organic use. After using this product, we will have to allow a transition period of 3 years before we can certify the crop as organic.

We used a moisture meter to track moisture and irrigated one of the beds reached 70%. The moisture test is very general, shown as a percentage of available moisture, but that should be good enough to allow us to compare one bed to another.

In 2014, the first treatment to drop to 70% was the bed mulched with chicken litter, and we ended up irrigating only three times.

I expected the 6” of woodchip treatment would prove to be the most weed free. However, quack got into and thrived in the deep woodchips, and turned out to be the most vulnerable to that perennial.

On the other hand, the bed that had the least perennial and annual weeds was the bed mulched with grass clippings. The original 3” of clippings reduced to only about 1”, but seemed to resist annual seed germination. In this bed, the plants grew (12-14”).

In the grass clipping bed, we observed growth of 6-8”. In the 3” woodchip treatment, the blueberry plants grew 12-14”. In the 6” woodchip treatment, most grew 12” long or longer.

It may have been a fluke that the quack thrived in the woodchips but hopefully the next 2 years will help us determine this. If the grass clippings prove to be the most useful they will also be the least costly and most readily available. It also makes one consider the possibilities of planting a particular seed mix in the pathways, then mowing them for mulch. An exploration of which seed mix would be best would have to be done.

After year one, I was glad I had designed a three year project; it takes the first year just to get the kinks out!

Back to top

2015 Results

In 2015, we still had problems with quackgrass, especially in the woodchip beds.

But we also encountered a bigger problem. The unusual open winter damaged most of our plants severely. In our area we had little fall rain and no snow to speak of. I believe we continued to lose soil and plant moisture throughout the winter. We watered one last time in the beginning of November and covered all plants with Agribon 19 Fabric – even our mature blueberry plants that were 3’ tall and as wide. In spring, I examined the plants and it was obvious that the stems were desiccated. As the weeks progressed, I noticed significant dieback in all plants, mature and immature. To say the least I was incredibly discouraged.

I hoped that plants would recover and come back from the roots but only 9 of my 24 project plants recovered. Some plants sent out small shoots, but they died mid-summer. Several times throughout the growing season I decided to stop the project, but then changed my mind. As the season concluded I was glad I did. There was interesting information to share.

We applied blood meal to the surface of the soil twice, once in mid-April and once in mid-May. We weeded several times, on an as-needed basis, and watered with a sprinkler. After we found the pH was still a little high for blueberries, we applied small amounts of elemental sulfur to the surface of the mulch around all plants. We decided to replace the plants that had winterkilled.

Treatment 1 (shavings) only one plant survived this winter. The shavings seemed to shed water like shingles on a roof. I decided I will not use this product again on blueberries.

Treatment 2 (grass clippings) We tried to keep the layer at several inches thick but they matted and broke down quickly. Five plants survived the winter, which surprised me, since losses were so much higher in the other beds. Interestingly, this bed was also the most weed free of all the beds. Weed seedlings did not germinate easily here and for some reason, perennial weeds were also easier to control in this bed. Maybe it was just a happy coincidence.

Treatment 3 (3” woodchips) In spring, it took one application to bring the bed back to the 3” level. However, only one plant in this bed survived the winter. We definitely had more problems controlling weeds in this bed, particularly quackgrass. No matter how much time we spent carefully hand digging out the roots, it came back with a vengeance.

We also did an extra soil test – the Solvita Carbon Burst Test – on bed 3. This test biological respiration – and, therefore, biological activity – in the soil. The test showed carbon dioxide at 4.69.

Treatment 4 (6” of woodchips) We added woodchips to bring it back to the 6” level this year. The plants in this bed sent more shoots up from the root systems than the other beds, making them thicker plants. Two of the six plants survived the winter in this bed. These two plants each had 18-24” of new growth.

Interestingly, organic matter increased the most in this bed and nitrogen was the lowest – yet these plants showed the most growth. This bed was a little easier to control the weeds in and it intrigued me to see what was going on at soil level. I moved aside the mulch and was surprised to see about a 1” layer of broken down black material between the chips and the soil.

In 2015 we also did the Solvita Carbon Burst test in the same bed in the same place and the biological respiration measure was 41.5 (compared to 4.69 in 2014). This is a tenfold increase, and if I understand the concept correctly, it means there was a tenfold increase in carbon sequestration.

To say the least, 2015 was an interesting year.

Back to top

2016 Results

We replaced the plants that had winterkilled last year, applied bloodmeal again in 2016 and watered when soil showed about 70% moisture capacity. We weeded as needed, which turned out to be about three times during the growing season. We applied mulch twice to maintain the desired depths of 3" chick litter, 3" grass clippings, 3", and 6" wood chips. The winter of 2015-16 was far kinder and we had little winter damage to the blueberries that had survived 2014-15, even though we did not cover the plants. The pH appears to be stabilizing; no additional sulfur was added. Please see the chart below for soil test results.

Soil Test Results

The Solvita Carbon Burst Test Report, showed the grass mulched bed to be most active, followed by the chick litter, the 6" mulch, and lowest, the 3" mulch.

Many of the issues we were looking at showed results all over the place and make it difficult to draw a conclusion. I will continue to use wood chip mulch, and will make it 6" deep when possible. I intend to supplement this with sawdust on some of the plants when I can get enough to apply it at least several inches deep and will be interested in seeing how this compares to the wood chips.

Category Tested Bed 1 2014 Bed 1 2015 Bed 1 2016 Bed 2 2014 Bed 2 2015 Bed 2 2016 Bed 3 2014 Bed 3 2015 Bed 3 2016 Bed 4 2014 Bed 4 2015 Bed 4 2016
pH 6.8 5.3 5.8
Organic matter (ppm)
2.9 3.1 2.6 3.8 2.9 4.2 2.6 2.9 2.4 2.8 3.5 2.7
Phosphorus (ppm)
136 200 196 156 152 162 99 152 102 148 154 108
Potassium (ppm)
289 408 139 199 210 181 98 267 113 207 204 156
Nitrogen (lb/A)





Back to top

Management Tips

  1. Soil test the year before you plant.
  2. Make sure the planting site is as weed free as possible before planting.
  3. On very sandy soil, overhead watering with a sprinkler system develops better root systems than drip irrigation.
  4. Covering the plants may not protect them from winterkill if there is insufficient moisture, no snow cover, and episodes of warming and deep cold. In other words, sometimes nature wins.

Back to top


  • Thaddeus McCament, Central Lakes College, Staples, MN
  • Eric Nelson, MN DNR, Brainerd, MN
  • Glen Borgerding, Ag Resource Consulting, Albany, MN

Back to top

Project Location

Redfern Gardens is located at 18298-270th St. Sebeka, MN 56477. Take Cty. Rd. 12 from Sebeka and go east for 4 miles. At the intersection of Hwy. 23, turn right, or south. Go 1 mile to 270th St. and turn left onto 270th St. Go 1 mile and cross the Redeye River. The first driveway on the left after crossing the river is the farm.

Back to top


eOrganic Website

University of Minnesota Extension Website

ATTRA. Blueberries, Organic Production.

Back to top

MDA Contact

Cassie Dahl

Ag Marketing & Development Division