If you burn a woodstove to heat your house, you probably know that keeping moisture in the air can be a problem for some houseplants. And while many folks are concerned with the frequency of application and the amount of water used for houseplants, there is another important factor to consider and that is water quality. What’s the effect of soft or hard water on houseplants?
Regular tap water is described as hard because it contains a variety of dissolved minerals. Water softeners swap the harmless calcium and magnesium in hard water for sodium. But sodium can present problems to both plant and growing medium.
First, sodium ions tend to break down the soil structure, which results in poor physical condition of the material around the root system. When this occurs, the potting material no longer drains well, and root problems can develop. Sodium can also accumulate in the plant. If the plant takes enough of the material from the soil, it may die. Sodium uptake is more of a problem where there is little or no leaching (flushing) of the soil mix after each watering.
If you do use softened water on your indoor plants, it’s important to use enough water at each watering to leach the soil around the root system. The leaching process is even better if you periodically can use rainwater or unsoftened water. In the event that leaching has not been done and the plants are in poor quality, it may be helpful to re-pot the plants with fresh potting soil.
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And if you do use a woodstove and generate a fair amount of wood ashes, those ashes can be the best or worst thing you can supply to the garden. Wood ashes are a source of potash, or potassium, and may help the garden. However, the chemical nature of wood ashes makes them caustic or alkaline. They are very similar to lime and will raise the soil pH higher than desirable if applied too often.
In the old days, water leachate created by passing water through containers of wood ash produced the lye needed for the homemade soap my grandma always made. The same lye will be formed to some extent as rainwater passes through the ashes applied to the garden soil.
The wood ash may also supply more potassium than the soil needs. I always suggest a soil test before any plant nutrients are added to the soil just to make certain that excess amounts are not applied.
If you want to use some of your ashes on the garden, I suggest that no more than a garden shovel of ash be applied per 100 square feet of area in any one season. This is not all that much, but most soils are not particularly low in potash in the first place. If you are not certain of your potash needs, it may be better to discard the ash in a non-garden area. You can use a shovel’s worth on the compost pile as well as the garden. I store my ash in large metal trash cans and use them out on areas that I am growing cover crops, since the pH of my soil tends to be more acidic and can stand to have the pH raised up.
Bill Lamont is a professor and extension vegetable specialist at Penn State and can be reached by email at firstname.lastname@example.org.