In July 2019, I wrote a blog post titled “Myths of the Gardening World“. In my head, I titled it “Gardening Myths I wish would die”, lol. And almost as soon as it was done, I thought of a few more that I had missed. These are myths I used to believe myself, until I did more research. So here, for your December dreaming of spring enjoyment, are a few additional gardening myths that need to be debunked.

Legumes (ie peas and beans) will feed nearby plants nitrogen

It’s often recommended to grow certain nitrogen hungry crops next to beans or peas, as its thought that the legumes will provide extra nitrogen for the surrounding plants. Turns out, that’s not how legumes work. The roots of legumes ARE capable of forming relationships with nitrogen fixing bacteria in the soil. These rhizobia bacteria take gaseous nitrogen from the air and turn it into a form of nitrogen the plants can use. In exchange, the plant provides food (carbohydrates) to the bacteria. This means that, when everything is working right, the gardener doesn’t have to provide supplemental nitrogen to the plants. So far, so good.

Those round bumps on the roots? That’s the root nodule made by the rhizobia baceria. It’s a good thing!

There’s not usually a huge amount of rhizobia bacteria naturally occurring in soils, so to boost this affect, gardeners buy a bean/pea “inoculant”, coating the seed with the powdered bacteria just before planting to ensure an adequate partnership. (Note that not every rhizobia works with every kind of legume, so its important to use the right kind for your crop.) As the bean/pea root grows, the rhizobia get to work, forming nodules on the roots, which is where the action happens. These rhizobia can persist in the soil for several years, so its not necessary to reinoculate the soil year after year if you are growing legumes in the same location.

But is there enough extra nitrogen being formed to benefit other non legume plants nearby? Studies are mixed, but if it IS moving through the soil, its in very small amounts, and depends on conditions not fully understood, including soil type, other available nutrition, moisture levels, other microorganisms etc. MOST of the nitrogen from the rhizobia association is stored in the legume plant itself. And then most of that gets used up when the plant produces seed. So even the left over plant residue, if tilled into the soil to feed the following year’s crop, will not have a huge impact on available nitrogen in the soil. Tilling in a “green manure” cover crop of legumes JUST as they start to bloom is the most effective way to have the soil benefit from the legume nitrogen stores. But remember, this residue will take a good while to break down and won’t be immediately available to the next crop. So green manures take quite a bit of planning.

So, yes, legumes can fix nitrogen when in the right association with rhizobia, but that nitrogen benefits the individual legume, not the plants nearby. Is it still worth inoculating your beans and peas? Absolutely. Just don’t expect them to make your corn grow better by association.

Mixed inoculant from Fedco Seeds

Coffee Grounds (or Pine Needles) will acidify your soil.

You see it often. A recommendation to put used coffee grounds or pine needles around your blueberry plants to help acidify the soil. The reality is that coffee grounds vary a lot in their acidity, depending on source, roasting and how it was brewed. A typical pH is around 6.7, which is just barely acidic (7 is neutral). By the time the grounds are fully composted, they are not going to be effective in changing your soil pH.

Pine needles are similar. They are only slightly acidic on the tree, less acidic once on the ground, not acidic at all by the time they have dried.

The best way to increase soil acidity long term is the regular use of sulfur around your nitrogen loving plants. Not even incorporating peat moss into the soil will have a long term affect on the pH of most alkaline soils. Cool citizen science study on that here.

Changing the natural pH of your soil long term is actually REALLY HARD. That’s because soil is actually made up of ground rock, and what is rock but minerals. Depending on those minerals, the soil itself can have a very large capacity to buffer acidic or alkaline substances, where their addition has little or no long term impact on the soil pH. For instance, there are areas with limestone soils (alkaline) that have received naturally acidic rainfall for millennia and yet the soil pH remains alkaline. Think about THAT the next time someone suggests you use coffee grounds on your blueberries. (Including used coffee grounds at up to 20% of your compost is still a good idea for lots of other reasons).

You can research your own property’s soil starting here. Read directions, then click on the green WSS button to start. You can REALLY go down the rabbit hole on this website. It will make your head spin. Our property’s soils are made up of Touchet Silt Loam, Ahtanum Silt Loam and Hermiston Silt Loam. The garden area is on Touchet Silt Loam. This soil came from alluvium flood plains, which means its a mix of materials, mostly silt, deposited by flood waters.

Knowing your soil type and base pH is important. I had a long time gardening consultant once tell me that the best thing you can do is focus on your soils nutrition, rather than trying to have a large impact on its natural pH. She may have had a point!

© 2020 Miles Away Farm, where we’re miles away from understanding everything we’d like to understand about soil health, but know that the answer to most problems is to add more compost!