Why Nursery Soil is Killing Your Houseplants
The people running your favorite greenhouse or nursery know a lot about plants. They know exactly how to help your plants grow according to their full potential. They have used their expertise to craft really thoughtful soil recipes for everything they grow.
Why then, do so many of us insist on repotting our new plants into a homemade potting mix?
The truth is that soil used in greenhouse production is optimized for exactly that: plants grown in a greenhouse. In most situations, this soil is entirely inappropriate for use inside our homes.
I am aware that a large portion of people grow plants for several years in their original soil and we will touch on why that sometimes works later on. For now, we will focus on why this is not a great strategy.
The many differences between a commercial greenhouse and your home:
Greenhouses are optimized for plant growth. They have been designed specifically to provide the perfect amount of light, warmth, humidity, and moisture for your plants to grow at maximum speed. They are the ideal environment for rapid growth. Under these conditions, plants will absorb and use the moisture in the soil at a MUCH faster rate than they ever will in your bedroom. This is what allows greenhouse soils to get away with being so “wet.”
Now, if you bring a plant home and place it in your sunroom or out in your yard (if appropriate for that species) it might be okay, but try placing that brand new fiddle leaf fig in a corner with no windows and you’ve got big problems. Most plants simply will not drink the water quickly enough and the extended wet period will result in degradation of the roots. You can mitigate this partly by watering very precisely, but this brings us to another reason why greenhouse soil is a poor choice for most indoor growers: greenhouse soil is generally designed to be used with drip irrigation.
Drip irrigation systems apply a measured amount of water and nutrients at a calculated rate that never allows the soil to dry out or get too wet. Of course, “too wet” in a greenhouse is very different than inside our homes. Since the plants in a greenhouse are constantly growing and taking up water, there is much less danger of overwatering and the soil can be held in a state of constant moisture with no ill effects. In our homes, we need to allow our plants to get much closer to dryness before watering thoroughly (for most species.) This is a fundamentally different watering strategy than that used by drip systems and, therefore, warrants the use of different soil mixtures.
To better illustrate what is happening here:
Let’s say you just ran 100 miles in a single day (well done!); can you imagine how thirsty you would you be?
Now imagine sitting outside for a few hours in the snow while you wait for your local dogsled taxi to pick you up; would it be a healthy choice to try and drink the same amount of water? Obviously, these examples are a bit extreme, but the amount of water that plants require in perfect conditions vs suboptimal conditions is huge.
Why am I making such a bid deal out of this?
The difference between a professional greenhouse and your bedroom is vast. The difference between the greenhouse and the far corner of your room, that gets no direct light, and averages 20% humidity, is incomparable. The more you try to provide the best conditions possible for your plants, the more wiggle room you have in terms of making the occasional error or mistake. The less optimal conditions you provide, the weaker and more vulnerable your plants will be. Combine greenhouse soil with low-light indoor conditions and you have a recipe for heartbreak and dead plants.
Root-bound plants: the saving grace
I do tend to make quite a fuss about soil recipes and growing conditions, but there is one factor that can overcome all these: a pot full of roots. If you keep your plant in the same pot for long enough, there will come a time when the root mass is so large, that it creates very favorable conditions in terms of drainage and aeration. The soil holds moisture, the roots do not. When the root mass becomes large enough, the ratio of roots to soil becomes very favorable. A large amount of roots can easily drink all the moisture in the pot within a reasonable timeframe. In other words, the root system has become a multi-marathoner and it is going to drink all of the water you can give it.
Getting your plant to this point is not always going to be easy. If the conditions you provide are good, the chances are higher. If the conditions are poor, the chances are low. The best reason to use a custom potting mix for your houseplants is to increase the chances and ease of successful growing. In general, your plant should completely dry out within 2 weeks and ideally, would require watering every 5-10 days. Anywhere in that range will provide a very healthy environment for (most) plants inside your home.
Final thoughts: if you’re not up for the task of repotting your new plants at the moment (understandable!) just make sure you are doing the best you can to provide optimal lighting and warmth. Humidity is helpful too, but I find that it is very challenging to raise humidity more than a slight amount so I would suggest focusing your efforts on light and warmth.
If you’re ready to start mixing your own soils but don’t know where to begin…you can check out some of my favorite soil recipes by following this link to a post that details my 3 favorite soil mixtures in 2020!
Cheers and happy growing!!!
