Hello friends, 
A couple months back I read a fascinating study by Michel et al. (2019) about how planting grass around blueberry plants can be more effective than traditional fertilisers. Here are the key study takeaways:
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Most soil is iron-rich, but the iron is mostly insoluble. Many plants secrete chemicals to make iron more soluble, either directly from roots or via soil microbes.
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Blueberries lack this adaptation, having evolved in unusually wet, acidic soils where iron is naturally dissolved.
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In dry or alkaline soils, blueberries often suffer iron deficiency, leading to yellowing leaves (chlorosis) and reduced growth, yield, and antioxidant levels.
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Grass intercropping provides a natural source of iron chelators via grass roots, making iron available to blueberries even in neutral or alkaline soils.
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The study compared grass intercropping (common meadow grass or red fescue) with:
- A āgold-standardā synthetic iron chelator (Fe-EDDHA)
- Cowās blood (Fe-heme)
- No treatment (control)
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Results showed grass intercropping was comparable to Fe-EDDHA in:
- Overall plant health (leaf color)
- Berry quantity and total weight
- Antioxidant content (anthocyanins)
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The main downsides of grass intercropping were slightly softer berries (possibly due to increased ripeness) and higher irrigation needs.
This method seems to offer an easier, more sustainable, and cheaper alternative to traditional iron supplements or soil acidification additives for blueberries.
For those interested, the study in full is available at: Frontiers | Sustainable Strategies to Prevent Iron Deficiency, Improve Yield and Berry Composition in Blueberry (Vaccinium spp.)
What are your thoughts on this approach? Has anyone tried grass intercropping with their blueberries?
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Nice write up. Iām currently trying this in my blueberry patch with around 18 bushes. Acidifying the entire area seems infeasible, so Iām growing a mixture of grasses to test this theory. I donāt think Iāll be able to tell how effective this is until next season though.
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If this was true, I would have less iron problems in my very weedy vegetable garden.
On the other hand, my dad has a bermudagrass problem around some of his vegetables, but he never has to apply iron chelate.
The problem I would see with this would be that the grass would choke out the blueberries. Youād need to plant a big plant.
Iām kinda intrigued though. Those grasses donāt grow in my area. I wonder if buffalograss or hall panicum would work.
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That wouldnāt work for me in the south using the two grass species they used in the study. The Creeping Red Fescue I have in my yard only survives the summer heat in areas where it gets shaded from the afternoon sun. The Bluegrass doesnāt do well in the south. That study started with high ph soil of 8.1 and needs a lot to get corrected to the plantās ideal preference. My native soil ph is 5.4 and the Southern Rabbiteyes do well without any addtional iron or adding sulfur to the soil. At least well enough for my uses.
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Iām in the fortunate situation where iron is typically not limiting in our soils and I have an unlimited supply of low pH and circumneutral iron available from work. Fixing Fe to an available form through other plants seems like a reasonable strategy if not at the expense of water and other nutrients.
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id be afraid that more aggressive weeds would get established in there and outcompete the blueberries. they have very shallow roots.
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Thanks for the post! Having read concerns of others I am thinking that this fall I will do a test of my blueberries with a planting of ryegrass which dies back in the warm summer months but adds significant organic materials and nitrogen to the soil during our wet winters here. Since it dies back it should not increase our needs to water it in spring. I think my main issue here is the highly alkaline municipal water we use each season. I have been adding both elemental sulphur and gypsum the last year to try to offset the alkaline water supply. In the two pics below you see a very healthy blueberry plant in foreground with a very unhealthy but similar age plant in the background.
Below is a closeup view of the unhealthy plant, notice the browning of leaves, some nutrient deficiency that may be iron.
This should be an interest test to see if after a fall- winter ryegrass growth, the same plants show the same results, or hopefully better next summer. If anyone has a clue as the what is causing the one plant to be unhealthy, please advise.
Dennis
Kent, Wa
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This brings up an interesting point though. If higher moisture levels allow more iron to be available to blueberries naturally, and intercropping with grass requires more irrigation, then the total benefit might actually be only partially from the grass and partially from the increased irrigation.
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Not sure about with other soil types, but at least with highly alkaline soil such as 8.1 ph, higher moisture levels in the soil only aggravate chlorosis issues (and donāt make iron that is in an unavailable form available).
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I think youād need to run the test for a few years to really measure if intercropping actually does anything. Sulphur can can take more than a year to actually break down and acidify the soil, especially in a cooler, drier climate where sulfur-reducing bacteria are less active.
Iām still fairly skeptical of the whole idea. Those are large, established plants you have. How much grass would it actually take to release enough iron to make a difference? Presumably a lot. And if the grass will grow and die in a season, howās the plant to get iron at other times? I believe in the study they used perennial grasses.
And perhaps more to the point, one of the main reasons blueberries need acidic soil isnāt iron. I mean yes, iron is important too, but thereās something thatās often more important. Nitrogen. Blueberries are mostly incapable of using nitrites or nitrates, which is why they are generally fertilized with urea or ammonia. But even when fertilized with those forms of nitrogen, a low soil-pH is very important. Urea, ammonia, nitrogen gas, nitrates, and nitrites in the soil exist in a equilibria with each other, as there are microbes that convert the different forms into the others. A low soil pH strongly favors ammonia-producing bacteria. A neutral or high pH tilts the equilibria the other way such that even if you fertilize with ammonia or urea, much of that nitrogen will get converted to nitrates and nitrites before the blueberries ever make use of it.
I personally donāt think thatās a soil problem. Are these the same variety? If so, then maybe one has something going on physically that the other doesnāt. A latent root girdling or root binding issue, a rodent living under it, a walkway compacting the soil around it and not around the other, etc. Alternatively, perhaps it is soil-related, perhaps the application of alkaline water or last yearās sulfur wasnāt even. To me it seems unlikely that the soil for plants that close together would be so different, but I also live in a much wetter climate, so the soil chemistry is a lot more uniform, what with all the rain and microbial activity moving stuff around a lot and evening out (and washing out) the soil chemistry. Iāve no idea what itās like out your way.
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I seem to have that same condition at times on some plants and have been attributing it to uneven irrigation. It looks like drought stress as talked about in this University of Michigan page.
Iāve improved my chlorosis issues by adding sulfuric acid to irrigation water.. The study mentions this a common practice but I donāt understand why they didnāt include it in one of their samples. They raise concerns that this method could hurt the soil microbe with nothing to back it up. Hope they are wrong!
I use rainwater for gravity-fed irrigation and having enough capacity is always an issue. I donāt want to use this resource on growing grass when a squirt of battery acid can more efficiently do the job. Iām still tempted to try adding some red fescue to one of a pair that still show signs of chlorosis.
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