, Newburyport, MA

January 29, 2014

Tim's Tips: Choose your potting soil wisely

Tim's Tips
Tim Lamprey

---- — Last week, I told you about fungus gnats on your houseplants. One of the things that can contribute to an increase in the number of fungus gnats is keeping the soil too moist. If the soil remains too moist, it may not be your fault.

If you read this column, you probably know what potting soil is used for when you garden. There are many different companies making potting soil.

Over the years, I have seen the evolution of potting soil from dirt added to a bag to a scientifically blended product that is specifically designed for a particular type of plant. You can find potting soils that are for cactus, and you can find soils that are specifically for African violets.

There are potting soils that are great for growing plants outdoors in containers. The soils that are best for growing plants in containers outdoors are probably not the best for growing houseplants. Let me tell you why this is the case.

Take a moment to think about growing plants outdoors in containers. The biggest challenge is keeping the soil moist during the summer months. The sun and wind can dry out the soil.

To overcome this problem, many of the potting soils that work well for growing plants outdoors have things added to the soil that help retain water. There can be granules that are added to the soil that hold water, or there may be materials added that hold water in the soil. Either way, the flowers or vegetables that you grow outside get the extra water that they need.

Your houseplants, on the other hand, don’t need as much water. Yes, they may be getting a lot of sun in your home, but they definitely aren’t exposed to the wind. If they are exposed to the wind this time of the year, you may want to consider buying new windows!

The winter months are also the semi-dormant months for houseplants. They may need more humidity for the foliage, but they are not taking up extra water through the roots. If you are using a potting soil that works well for outdoor plants, it probably isn’t the best soil for your houseplants. The ability of the outdoor soil to hold onto the water means that your houseplants have too much water being retained in the soil.

Soil that stays wet all the time will definitely contribute to an increase in fungus gnats. If you use a soil that holds extra water as a soil for your cactus and succulents, they will be at an increased risk for rotting during the winter months.

So where is all of this going when it comes to potting up your houseplants? When potting or repotting, you always want to use a potting soil that doesn’t have anything added to hold extra water. If the soil naturally holds some water, yet allows the excess water to drain away, then you will have found the best potting soil for your houseplants.

Well, that’s all for this week. I’ll talk to you again next week.


Tim Lamprey is the owner of Harbor Garden Center on Route 1 in Salisbury. His website is Do you have questions for Tim? Send them to, and he will answer them in upcoming columns.