Houseplants 101: 7 Reasons Your Houseplant Is Not Thriving

By David Graper
SDSU Extension Horticulture

So, you want to grow a house plant? Maybe you received a beautiful orchid as gift from a friend, or your mother-in-law has given you her beloved snake plant to take care of while she spends the winter in Florida. You may even be interested in growing a plant in your home purely for your own enjoyment. Whatever the reason, you are having doubts about your ability to care for this plant properly, as your past record is less than stellar. Remember what happened to the last plant that you tried to grow?

7 Reasons Your Houseplant is Not Thriving

Have no fear! It is time to push those doubts out of your mind, and equip yourself with the information to create a thriving green oasis in your own home. A great house plant is not only beautiful and enjoyable, but also functional. House plants create a relaxing and inviting atmosphere, yet are notoriously difficult for many people to maintain. Armed with a little bit of knowledge, presented in this article, anyone can enjoy a variety of houseplants for years to come.

It is time to dive into the nitty-gritty of why you may have failed in the past, and how you can be sure that your next experience growing an indoor plant is a positive one. We first need to establish a base of knowledge from which we will build upon going forward. All house plants are subject to five key variables that make up the indoor environment. These variables are temperature, humidity/water, air, light, and soil. Keeping these variables in check will ensure that your plant will remain happy and healthy long after you bring it home from the store. The following seven statements will deal with these variables, and how they pertain to house plant health.

1: Over-watering

Perhaps the number one cause of death for house plants worldwide is over-watering. While it is true that a plant will die if you do not water it for extended periods of time, it is also true that you can drown a plant. Excess water will cause the roots to rot and eventually die. Additionally, plants need air, and excess water will suffocate the plant. Ensure that your house plant is in a container with drainage holes that allow excess water to escape. A good general rule is to allow for the soil to mostly dry out between watering. You can tell when the plant is ready for more water by sticking your finger into the soil up to your first knuckle. If the soil is dry, saturate the roots. Make sure the excess water can drain freely from the pot and not be left in a pot saucer where it can still cause root rot by limiting oxygen in the potting soil. This method of watering will help prevent over and under-watering. A notable exception to this rule is succulents and cacti which should be allowed to dry out thoroughly between watering.

2: Poor Soils

The type of soil that your house plant is growing in matters a lot for the overall health of your plant. Your typical backyard “dirt” or garden soil will not be able to sustain a house plant long-term. The soil that you use should be indicative of the type of plant you are growing. The reason that any old dirt will not work for your house plant has to do with the watering issues that we talked about previously. As a general rule, your indoor houseplant soil should be pasteurized to ensure no weed seeds or pathogens are present, provide good aeration so the roots can remain healthy, and have a good water holding capacity without holding onto water for too long. Custom and standard soil media mixes are available at local retailers, and care should be taken to select the proper mix when potting indoor plants. Your plant can only be as healthy as the roots, so ensuring good soil is critical. The image below shows a standard greenhouse growing mix which contains some garden soil and is pasteurized; typical potting mix components of peat moss, perlite and vermiculite; and a commercially available potting mix. Peat moss is used for moisture and nutrient retention. Perlite adds air to the mixture. Vermiculite is used for its water holding capacity. Compost may also be added to provide additional nutrients.

3: Lights, Lights, Lights

Everyone knows that plants need light to grow, and that sticking them in a closet is probably not the best idea, but how do we know how much light a plant really needs? The answer to that is not as straight forward as previous answers. Some plants will tolerate relatively low levels of light (200-500 foot candles) while others need much higher levels (2000+ foot candles). Additionally, there is a difference between the plant not dying and the plant growing and blooming.

Plants can sustain themselves for extended periods of time with slow to no growth if they are receiving light on the lower end of their comfort zone, which is common in many home situations where they do not receive much direct sunlight, possibly just some light from a ceiling light fixture. I cannot tell you exactly how much light your specific plant needs in this article, but what I can tell you is that the label that came with your plant is probably a good starting point. Placing a plant on the south side of the house will be better for the plant than putting it on the north. Choosing a plant based on the light required is another good practice. A simple internet search can point you in the right direction of where you should place your new green roommate. Changing up the location of your plant might just give it the boost it needed. Once you find a place where the plant is doing well, leave it. Some gardeners may even choose to invest in a newer LED plant light that provides a nearly ideal spectrum of light that will help plants to thrive.

4: Temperature & Humidity

The typical indoor environment is much different than the native tropical/subtropical environment that most common house plants originate from. The closer we can mimic that environment the better (within reason). Two key aspects to take into consideration are temperature and humidity. First off, the temperature in your home or office obviously cannot be tropical, but that is okay. House plants will do just fine at “room temperature” in the 60-80 degree range. What is important is to minimize temperature fluctuations due to drafty windows/doors or heat/air exchange vents. This not only stresses the plant temperature wise, it also can dry out the plant rapidly. Or, a cold draft may damage sensitive plants. That brings us to the second part of this topic, humidity. Tropical plants come from humid areas, and it is important not to forget this. Winter conditions in the typical residence tend to be very dry, stressing the plant and causing it to dry out more rapidly. The addition of a gravel tray to increase humidity will do wonders in helping to prevent common house plant problems such as the edges of leaves dying and mites.

5: Your plant has bugs!

Don’t freak out just yet! House plants can, and often do, have insect problems. This does not mean your house is dirty or that you should toss the plant into the garbage. The problem may have originated when you brought your plant outside for some fresh air in the summer or the pest could have hitched a ride on your shirt sleeve on your way home from work. The plant may have even come to you with this problem and you didn’t realize until it became worse. Whatever the reason may be, this is not the end of the world. As common as the pests themselves are the treatments. A little research into the critter will provide you with a strategy to eradicate the infestation. Below are the tell-tale signs of common insect problems.

Spider Mites: Spider mites are actually not insects, but related to spiders. They feed by sucking sap from the leaves, causing tiny yellow spots to develop on the leaves. Webbing may also be visible. The mites themselves are so small they are often very hard to see.

Scale: Scale insects look like bumps on the leaves or stems of your houseplants; they also suck plant sap. They excrete a waste product called honeydew that is sticky. Sometimes the honeydew will become infected with sooty mold that will turn it black, so watch for that too.

Mealybugs: Mealybugs look like little tufts of cotton. These are also sap-sucking insects that also excrete honeydew.

6: Your plant is starving

Plants, just like humans, need food to survive. For a plant, “food” comes in the form of nutrients in the soil. If your plant is potted in a small container, or a large container for that matter, you can imagine that eventually all the available nutrients will be gone. When this happens, your plant will begin to struggle. No available nutrients in the soil means that your plant does not have all of the resources it needs to grow. Supplemental plant food and fertilizers are available at local retailers and will greatly help the health of your plant. Just be sure to follow the instructions for how often to apply your specific fertilizer. These products may be a slow-release product that you sprinkle on the potting soil, or a liquid or powdered concentrate that you mix with water before applying it to the plant.

7: You picked the wrong plant

Indoor plants have well documented, preferred growing condition needs, and if these are not met the plant will not thrive. A critical aspect of successful indoor gardening is making sure you pick the right plant for the spot. Just because you like the looks of a particular plant does not mean that plant will like the spot you have for it at home. Analyzing the light, temperature, air, soil, and humidity of the spot you have at home is important before plant shopping. If you have a low light area, and try to grow a plant whose tag states full sun, that plant will not do very well. It seems like common sense, but those tags are on there for a reason. You can choose to ignore the recommended care instructions, but you will see the consequences.

Growing houseplants is for everyone! You don’t need to be a master gardener to enjoy the benefits of a great house plant. All you need is a willingness to try a few things and do a little research. Just because your first couple attempts to grow a house plant failed doesn’t mean that you should give up. I hope that this article has provided you with the motivation to get a house plant of your own. This article is not a complete guide to house plant care, but rather a guide to get you started. Each one of the above 7 reasons could be (and probably is) its own book. The internet is a wealth of knowledge, and should be used!