Garden Help Desk: Do pine needles poison soil?

Pine straw is a common mulch in some regions of North America, but forr Utah County gardeners it's only readily available if you 'grow your own' or have a friend with conifers in their landscape.

I removed an old ever-green hedge which has left a lot of needles in the soil. I am replacing the hedge with boxwoods. I have been told that the needles poison the soil. If this is the case, what do I need to do to prepare the soil for my bushes?

There is a persistent and common gardening myth that evergreen needles will make soil acidic and damage other plants. The notion probably comes from the fact that plants struggle to grow under conifer trees, but that isn't caused by the acidity of the needles that drop from the trees.

Evergreen needles don't poison the soil or make the soil more acidic. If you’ve had plants that struggled to grow under your evergreen trees, it's most likely because they had to compete for moisture with the numerous shallow roots that are common with conifers. The dense shade under evergreen conifers is another reason why it can be such a challenge to grow many of our most popular annuals, perennials, and ground covers under these trees.

Don't worry about needles poisoning the soil. The needles don't contain any poison. They are quite acidic though when they first drop from the trees. Any acidification would be a good thing for our alkaline soils, but most Utah soils are so buffered (resistant to change) that any acidification from the needles is very minor and temporary. The needles from pine, spruce, fir and cedar trees also become less and less acidic as they decompose, further limiting any potential for reducing the pH of our soils.

If the layer of evergreen needles in your shrub bed is so thick that you’ve got mostly needles and very little real soil, then you might consider clearing away the upper layer of needles and adding them to your compost pile. Up to 10% of the volume in your compost pile can be evergreen needles. Or you can use those excess needles as a surface mulch after you’ve planted your new shrubs, because the needles make good mulch for reducing weeds, slowing evaporation during the summer, and insulating the soil during the winter.

Pothos and many other plants will develop aerial root nodes along their stems. The nodes aren't a cause for concern.

The partially decomposed needles at the bottom of the layer can be incorporated further into the bed to create a uniform soil that is rich in organic matter. You’ll end up with a shrub bed with loose, workable soil that has improved drainage, moisture retention, and soil structure.

What is wrong with my philodendron plant? It has started getting dark bumps on the stems. What can I do to save my plant?

Based on what I can see in your photo, your plant is a pothos, a popular houseplant because it is so tolerant of all kinds of lighting, watering, and temperature conditions. A pothos will even put up with some neglect. Philodendrons are similar in leaf shape and growth habit, but these are two different species.

The brown bumps on the stem are nothing to worry about. They look like ordinary arial root nodes that normally form on pothos stems as they mature. Not every indoor plant will develop these root nodes, but you might see similar roots on other indoor plant species now that you know what you’re looking for.

If you were to take a leafy stem cutting from your pothos that has root nodes and tuck that cutting into a glass of water, you would eventually see roots develop from those nodes. You could plant that rooted cutting back into the pot with your original plant or plant it in a new small pot as a separate plant.

Even though a pothos will tolerate a variety of conditions and a little neglect, your plant will do best in a draft-free location with moderate to bright indirect light, and thorough watering whenever the upper inch of soil is dry.

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