Archive for January, 2011

Mulching with pine needles

I’ve been spending my rainy winter days making a master plan for my garden, and I’m hoping to get some more fruit in there, since a small handful of berries lights up Brian’s face in a way that a whole wheelbarrow full of chard and onions never will. Because of this, blueberry bushes have been popping up all over the place in my garden plan. Advice abounds telling me to put blueberries in acidic soil, and how I can easily change the pH of my soil by mulching with pine needles. Since I have to rake pine needles off my deck anyhow, mulching with pine needles sounded great- but then I started reading about how the claims of pine needles changing soil pH were untrue.

Before I get to the shocking conclusion about the effects of mulching with pine needles, let me quickly remind you what the pH scale is all about. A pH less than 7 is acidic, and a pH more than 7 is more alkaline, which is also sometimes called basic. From a chemistry perspective, pH all adds up to which ions the soil has an excess of, especially the ions that add up to water, H+ and OH (it’s not just a coincidence that the letters add up to H2O). Don’t remember what an ion is? Ions are charged particles, and when it comes to soil science, ions are usually the product of dissolving something in water. Some essential plant nutrients are present in damp soil as ions, including calcium, magnesium, and potassium.

A few of the things that effect native soil acidity are heavy rainfall, the parent material of the soil, and the amount of decaying organic matter. While those factors add up to generally acidic soil in Western Washington, who knows how much of the dirt I’m gardening with was naturally deposited on my little plot of land and how much was hauled in.

So do studies show that mulching with pine needles increase acidity? It depends on which study. Some folks have seen slight decreases in pH (which means increases in acidity), and others haven’t seen any pH effects. Does this mean that some of the studies must be wrong? Of course not- whether a mulch or soil additive will change the pH of a soil depends on lots of factors, including the amount of rainfall in the area and especially the composition of the soil. Some soils have more buffer capacity, which means that they are more able to resist changes in pH. Clay soils are known for their ability to resist pH changes, as opposed to sandy soils.

Am I going to put those pine needles that I raked off my deck around my blueberry bushes?  You bet I am. My pine needle mulch may not make the soil acidic enough to keep my blueberry bushes happy, but at least it will help smother the weeds.


[1] M.L. Duryea, R.J. English, and L.A. Hermansen, “A comparison of landscape mulches: Chemical, allelopathic, and decomposition properties,” Journal of Arboriculture, vol. 25, 1999, p. 88–97.

[2]Raising Soil pH and Soil Acidification


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Snowstorm Harvest

My new favorite winter vegetable is bok choy. I needed some vegetables for my fried rice tonight, so I went out to raid the garden while the snow was still only about a half inch deep and nabbed some little bok choys.

I sowed seeds for these in late August. For 4 months of growth, these guys are tiny, but what’s more important is that they were tough enough to make through the cold nights and snow to be in my dinner tonight.

The plants are the “Ching-Chiang” variety. The instructions that came with the seed packet recommend planting in early spring, which I tried last spring, but all my plants bolted when the leaves were about the size of my thumbnail. The variety is also described as very mild, but I found them pleasantly spicy. The slugs also find them delicious, which is another advantage of growing them in the winter, since the slugs pretty much take the winter off.

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The other day I was browsing Etsy for garden art, and came across some beautiful whimsical bird feeders, and was about to buy them when I thought, “Wait- should I even be feeding the birds?”

What are scientists saying about bird feeders? It definitely can make a difference in both the survival and behavior of birds, but calling those changes good or bad is tricky.

A few of the effect of feeding birds that researchers have figured out:

  • Feeding birds during the winter and spring can cause birds to lay their eggs earlier, lay larger eggs, or have larger clutches. Both laying earlier and larger eggs tends to increase hatching and survival rates. Like all the other results I’ll mention, some bird species seem more susceptible to these changes than others. The magnitude of these effects also depended on the quality of the food provided to the birds- in a study of Florida Scrub Jays, birds fed high-fat high-protein diets layed first, birds fed high-fat low-protein diets layed next, and the control group that had only food that they foraged layed last. Extra food makes the most difference in tough environments such as cold winters and poor-quality habitat.
  • Adult birds sometimes feed their chicks the human-provided food, or sometimes eat the provided food themselves, which allows them to give more of the food they forage to their chicks. Unsurprisingly, when the chicks themselves receive the human-provided food, high-quality food has a positive effect on the growth of chicks, but low-quality human-provided food can have a negative impact on the growth of chicks. This is one of the clearer lessons in whether feeding birds is a good idea- for those who are tempted to toss bread crumbs or other human food out for the birds without considering whether it is nutritious to birds, consider that you may be doing them more harm than good.
  • Fast growth in chicks is considered good, but once birds are adults, many bird species regulate their weight to balance their perceived risk of starvation with the ability to get away from predators quickly. At first glance it may seem like if feeders aren’t constantly full, we’re messing up the birds’ body-weight calculations, or if they are always full birds might become dependent on them, but we should remember that most birds expect to get food from several different places. Even when easy food is available in a feeder, most birds will also keep track of several other patches of food, expecting some of them to disappear now and then. This lack of dependency was confirmed for black-capped chickadees in a study during a Wisconsin winter, where feeders were suddenly withdrawn, and chickadees that had previously used the feeders did just as well as ones who hadn’t. The authors point out that since the study was done in a rural area, where natural food may be more available than urban areas, the results might not hold true for cities. Since Seattle gets very little snow in the winter, I’m guessing that even the city gardens in my neighborhood have plenty of natural food for little birds like chickadees to get by.
  • Some folks are concerned that bird feeders increase the number of little birds getting eaten by predators. It turns out that how many birds are caught by predators depends on how and where your feeders are set up. Overall, though, researchers actually think that little birds get eaten at feeders less often than they would in the wild. The biggest predators at feeders are hawks and cats, though if you have eagles or snakes in your yard, they might be your biggest suspects. The feeding setups with the highest levels of hawk predation are near deciduous woods, have large feeding areas, year-round feeding, and lots of feeders. Cats got the most birds when bird feed was on the ground. If you want to prevent your cat from eating birds, put a bell on your cat, and keep bird food off the ground. Especially since bird feed on the ground is also rat food.
  • Researchers know that some diseases and harmful microbes spread through feeders, including mycoplasmal conjunctivitis and salmonella. To prevent this, take your feeder down and give it a good washing with hot water and soap, making sure to thoroughly rinse out the soap. For the same reason, wash your hands after handling bird feeders.
  • The ranges of several birds has expanded in the last 50 years, as bird feeding has become more popular, and some bird populations are overwintering in places they used to migrate away from. There are a few things that could explain these behavior changes, but feeding of birds is the most likely cause for many populations. All of the earlier issues I mentioned set off little red flags in my brain, but as someone who’s studied how plants, animals, and diseases spread, changes in range and migration patterns set off big warning bells. Messing with the physical location of species tends to wreak havoc in ecosystems, and though I’m not a bird expert and can barely guess what changes have occurred due to these behavior changes, I’m not excited about contributing to this experiment, even though those feeders were adorable.

While all this research has convinced me not to put a bird feeder in my garden, it leaves out the main reason other people choose to have them- they like to see birds. Just like owning a dog doesn’t make economical or environmental sense, there are other, more social benefits to having animals around to entertain us. My squeamishness about causing ecological change may also be misplaced, since gardening is at its heart, creating my own little ecosystem. I think I’ll take the middle ground this time though- I’ll design the plants in my garden with feeding the birds in mind, with native berries, seeds, and flowers making a strong showing and a clean pool of water in the bird bath year-round. Maybe I’ll even get those little bird feeders, but hang them empty as garden art and let the plants feed the birds.


[1] M.C. Brittingham, S.A. Temple, “Does Winter Bird Feeding Promote Dependency?,” Journal of Field Ornithology, vol. 63, 1992, pp. 190-194.

[2] E.H. Dunn and D.L. Tessaglia, “Predation of Birds at Feeders in Winter,” Journal of Field Ornithology, vol. 65, 1994, pp. 8-16.

[3] G.N. Robb, R.A. McDonald, D.E. Chamberlain, and S. Bearhop, “Food for thought: supplementary feeding as a driver of ecological change in avian populations,” Frontiers in Ecology and the Environment, vol. 6, Nov. 2008, pp. 476-484.

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