If you are blessed with a natural green thumb, then continue doing what you’re doing. But if you’re like the rest of us mere humans, it takes time and a lot of trial and error to figure things out. It’s important to know some indoor gardening basics to give you the best chance to grow gorgeous plants.
Save yourself some of the hassle by understanding the principles of what’s going on above and below the dirt. While you could come back to this after killing many of your plants, why not start out with an indoor gardening guide to give you all you need?
We’ll take a look at how plants grow, then dive into actionable tips on what you need to do to promote healthy growth even as a beginner. Anyone can learn how to garden indoors!
How Do Plants Grow?
Most likely you will buy a plant from the store or acquire it from someone else already fully grown. And while we’ll cover adult plant care a little further on, let’s start at the very seed of the process – from the seeds themselves.
Growing a plant from seed is a wonderful process, and armed with some indoor gardening basics, it’s pretty easy too.
Stages of Plant Growth
There are definitely stages to the growth of every plant. We don’t usually think about them a lot. You just stick a seed in a pot and a plant appears, right? But there’s different needs at each stage which should be met.
The seed itself is a fascinating thing. In one little shell is contained not only the beginning of the plant, but what it needs to sustain itself until it can form a root.
There are three “basic” parts of a seed: the seed coat, the endosperm, and the embryo.
What we see when we look at a seed is merely the seed coat. This thick exterior provides protection for the future plant.
From there, the endosperm provides all of the nutrition that the plant is going to need initially. This completely surrounds the embryo in most seeds, providing easily-accessible sustenance. It’s not just for plants — we eat endosperms too! Anyone who’s had popcorn or white rice has munched on delicious endosperms.
Finally, there’s the embryo itself. There’s three major components to an embryonic plant: the roots, the cotyledon, and the embryonic leaves. All of these are tucked inside that tiny little seed.
We all know what roots are, of course. The cotyledon is an external food source for the plant once it emerges, and the embryonic leaves are usually the first two leaves that appear once the seed germinates.
If you store your seeds in a dry, airtight location, they won’t move on to future phases until conditions are right. Seeds can be viable for years, although the endosperm will gradually decline over time and reduce germination.
Germination is when the seed stops being shy and comes out of its shell. Two conditions need to be met for a seed to germinate:
- Water. Seeds soak up water and rehydrate, which triggers the growth process.
- Warmth. Different plants require different levels of heat to germinate properly. If it’s too cold or too hot, the seed will decide to stay dormant.
Germination can take anywhere from a few days for most vegetables to weeks for some trees. Here’s what can inhibit germination:
- Planting the seeds too deeply. Make sure to follow the instructions with your seeds and don’t just throw any amount of soil on your plants. Some seeds can be placed on top of the soil. Others want to be under the soil’s surface.
- Poor quality seeds. Seed manufacturers have to test their seeds for germination rates to ensure they aren’t selling a bunch of duds. Stick with organic and non-GMO seed distributors to ensure the highest quality. And if you have leftover seeds from a previous season, test a small handful of the seeds – if they germinate well, then go for it.
- Too much or too little water. Most seeds like evenly-moist soil to sprout in. If it’s too dry, they’re not going to germinate. Too much water can actually drown the young plant!
When the seed first germinates, it relies on its endosperm for initial growth. It sends the root into the ground to establish a support system that will draw upon nutrients from the soil to allow it to grow further.
Now that the seedling has grown its roots downward to absorb soil nutrients, it needs to stretch its leaves so it can start gathering light to produce the energy it needs.
During the vegetative stage of growth, plants grow their stem, branch and leaf areas to reach light areas. They grow more leaves and bigger leaves so they have a greater surface area to absorb light.
While doing this, they’re hungry for nitrogen (N on the N-P-K fertilizer labels) to produce chlorophyll, the material that allows the plant to absorb energy from light. Fun fact: most chlorophyll is green, giving many plants their green color!
The reproductive phase is when the energy that was going to plant growth is now dedicated to flowering or going to seed. During reproduction, phosphorous is an important nutrient, as it assists with flowering or fruit growth.
This phase can be triggered by a change in length of daylight. Plants are sensitive to these changes, and the sensitivity itself is called photoperiodism.
But plants just notice light itself, not where it comes from. That’s why artificial lighting can be used to control growth of plants indoors. As long as there’s a good spectrum of light that’s similar to natural sunlight, your plant will grow.
In this stage, you will also find pollination, which is how plants start to develop seeds and reproduce. If you have an indoor garden that needs to be pollinated, that means you have to pollinate them yourself.
Most people do this with a cotton swab, gently brushing it against the interior of a flower and then moving on to the next flower and the next. It’s not a difficult process, and isn’t necessary on plants you don’t want to fruit or that you’re not collecting seeds from.
People who grow perennials (plants that live more than a year) know about dormancy. It’s a stage of the lifecycle that’s often overlooked, since annual plants don’t have it, but it’s good to know about. In this stage, a plant can suspend its growth until a better growing environment is achieved.
You can think of this as a type of hibernation during the winter months or the summer heat. This period of dormancy can make them look like they are dying. However, they’re conserving energy until an opportune time. Smart little suckers right?
Dormancy happens naturally as seasons change due to lower hours of light during winter and colder temperatures. For cold-loving plants, dormancy can also happen through the summer months, and the plant will come back once the heat subsides.
Indoor plants might not have as much of a winter dormancy period as outdoor plants but it can still occur from December – February in the U.S. Thankfully for us, summer-dormant plants seem to like our cooler temperatures indoors, so they may not go dormant at all.
During dormancy, withhold fertilizer and water less because the plants will not be taking up as much compared to the rest of the year.
If your plants really decline when you start giving them less water + nutrients, then they probably aren’t going through a dormant period and you should treat them normally.
By now, you have a good understanding of stages of growth! So let’s jump in to other critical information about how a plant grows.
Understanding The Roots
While we may admire a plant or tree for what’s above the ground, what’s underneath the ground is where the magic happens.
Roots are the IV of the plant. They absorb the air, water and nutrients from the soil and transport it to the leaves for photosynthesis (which is how they produce their energy to grow).
If the roots don’t have adequate space to grow, then the plant, tree, whatever it is, will reach a certain size and not be able to grow any further. It’s like limiting your calories to only what your body needs to maintain the same weight. Since you aren’t getting any extra calories, then you can’t grow.
However, if your plant is growing great and then looks sickly, that could be a sign that your roots need room to grow to support the plant. Now would be a good time to repot the plant.
On the flip side, indoor gardeners can run into issues where they have too much space for the roots to grow.
Too big of a container is called “overpotting”. The problem is not with the roots but ultimately too much soil. Whenever you water your plant in a larger than needed container, the water sits in soil that can’t be absorbed by the smaller root system. This reduces the aeration of the soil and causes the roots to rot rather than expand. It doesn’t happen in nature because the soil drains much better.
And what happens if you damage the roots of your plant? The good news is that a plant can regrow their roots if damaged. The key is how much of the root system is damaged. If there aren’t enough roots for the plant to draw in enough life (water, nutrients, air), then the plant will wither.
Understanding The Leaves
Leaves are biology’s masterful solar panels that convert light to energy for the plant. If you want to get into the technical details, the process of photosynthesis actually produces glucose which fuels the plant. But you remember that from school so we don’t need to get into that right?
Leaves are actually wonderful communicators. The problem is we are bad listeners. Here’s how to know what you plant needs by listening to the leaves:
- Starting to turn yellow? Your plants need less H20 or more nutrients! First, try watering your plants a little less often but still giving them enough water (don’t punish them for turning yellow on you). If they continue to turn yellow, then that could be a sign of a nutrient deficiency and they will need some plant food. Read more about plant nutrients.
- Brown and crunchy? Your plant needs more H20! Don’t overwater them but make sure the soil is damp. Find the right consistency of water where the soil continues to dry up but the leaves aren’t turning brown and crunchy.
- MIA (Missing in action)? Your plant needs more H20 or sunlight! When there isn’t enough water or sunlight, your plants can’t do photosynthesis and so will not develop any new leaves or grow. Test giving your plants some more water first. And if that isn’t working, then try getting them some more light as well.
- Developing yellow spots? Pests can get to indoor plants just like they can to outdoor ones. If your plant’s leaves are starting to form yellowish spots, you may have a spider mite problem. Scale also can happen indoors and can cause other problems.
What Do Plants Need To Grow?
First, let’s look at the scientific requirements.
The 5 Things Plants Need To Grow
- Light. Plants use light as energy to turn water, carbon dioxide and nutrients into the sugar that they can eat, a process known as photosynthesis. When they have low levels of light, they can be starved because there is no energy for them to make their own food.
- Water. Needed to perform photosynthesis and enables the plant to draw nutrients from the ground. Water also provides necessary humidity around the plants.
- Carbon Dioxide. Plants breathe in the carbon dioxide in the air around them to use for the photosynthesis process.
- Growing Medium. Most commonly soil, plants need something to dig their roots into so they can hold themselves upright and draw upon nutrients from the growing medium.
- Nutrients. Just like humans need nutrients for good health, plants require nutrients which provide a variety of functions such as aiding photosynthesis or helping them build a strong root system. All plants require different levels of nitrogen, potassium and phosphorus to live.
Now that you have your fundamentals down, let’s jump into the actionable tips.
Soil + Fertilizer
Soil is dirt that is “alive”. It contains nutrients, organic matter, water, air and even living organisms like bacteria or fungi. The soil is necessary for indoor plants so they can draw upon the nutrients in the soil to live. Dirt is “dead” matter and has nothing to offer them.
What soil should you buy? For indoor gardening, it is highly recommended to use an organic potting soil rather than soil from your garden which can bring pests and plant diseases into your home or greenhouse. Here’s a list of best potting soil for different types of indoor plants.
How long does soil last? Check the “Best if used by…” date… okay, I’m kidding, you won’t find one of those. Soil can still be usable years down the line, but the nutrient content might be depleted from microbes eating it. Refer to the fertilizer section on how to ensure the soil will have the nutrients it needs.
How should you store your unused potting soil? When not in use, put your soil in an opaque tub and put the tub in a stable, dry area like a garage or basement. You don’t want the soil to get wet and you don’t want to keep it in an area where it can get common garden pests or become infected with bacteria. Check your soil every few months to make sure it’s in good shape and isn’t spontaneously growing anything.
Fertilizer is a concentration of nutrients to replenish the original nutrient content of the soil. If you don’t understand why that’s important, reread the “how do plants grow” section.
Fertilizer can come in many different shapes and sizes: could be a packaged fertilizer, maybe some worm poop and even your own poop could be fertilizer (that’s why I said many different shapes and sizes…too far, sorry).
For the basics, most fertilizers are talked about in “N-P-K” which stands for Nitrogen, Phosphorus and Potassium, the essential nutrients for a plant to grow. Different fertilizers can have different NPK ratios to feed different types of plants.
What fertilizer should you buy? Depends on the plant but the best bet is to get organic fertilizer. These are made to improve your soil over time, unlike synthetic fertilizers which can slowly degrade soil quality. Check out this guide to organic fertilizers to find the one that you need.
How should you apply fertilizer? Water your plants before you add dry fertilizers so they are ready to absorb the nutrients. And then follow the instructions on the package on how often you should use the fertilizer.
- If you are using a packaged fertilizer that is not specific to indoor gardening, consider using only 1/4 to 1/2 of the recommended dosage since you’ve got a smaller amount of soil to fertilize.
Liquid fertilizers can be used when diluted to a houseplant strength (check the label), and should replace a regular watering.
Should you “flush” your plants? Fertilizer nutrients get absorbed by the plants but other parts of the fertilizer will sit in the soil which can have adverse effects. If you have drainage in your pots, consider heavily watering them and letting them fully drain out on a monthly basis. This will flush out the extra fertilizer parts and keep your soil healthy.
I don’t need to tell you that you need to water your plants. But because overwatering is the most common cause of death for indoor plants, let’s make sure you are watering your plants not too much, not too little, but just right.
When should you water? Don’t focus on how often, focus on how much. Pay attention to the leaves as mentioned in the How do plants grow section. Also, pay attention to the soil. Does it still look wet? Does it still feel wet on top or if you stick your finger in the soil?
If it’s still wet, you don’t want to keep watering the plant. The water needs to drain so that way it doesn’t become stagnant and lead to mold. If you put way too much water in your container, then you risk drowning the plant too because the plant’s roots still need air.
How should you water your plant? Some plants do best with bottom watering (with moisture “wicking” through the soil) while other plants will do best with pouring water directly on the top of the soil. Since it is so dependent on the variety, research what will work best for your specific plant. When in doubt, opt for bottom watering as the biggest roots should be able to reach.
Do you need drainage? If overwatering is the number one cause of death for indoor plants, drainage could be argued as the number one lifesaver for indoor plants. Drainage accounts for your mistakes in watering. The rule of thumb is that you should absolutely incorporate drainage if you can. Some plants are easier to take care of so you can risk it if you’d like, but it is easier on your if you just have some sort of drainage hole.
If you don’t have any drainage, what should you do? Be conservative in how much water you give your plants and pay attention for how long it takes the soil to dry. Does it dry within a few days? That’s good for most houseplants. If the soil is staying wet all week, then that’s a sign you need to figure out a better solution for improving air flow or watering less.
If you are growing vegetables or microgreens indoors, you want dry soil sooner than a few days because they are more prone to developing mold in a shorter time frame.
Keep in mind, it’s easier to bring back a dying plant from under-watering than a dead plant from overwatering.
Ah, you can’t talk about watering without talking about air flow. Air flow and water are the two major influencers of plant mold and diseases. Air circulation enables water to evaporate quicker and prevent mold growth which is essential when you are growing your own food indoors.
How much air flow does a plant need? You don’t need to always have a fan blowing directly on your plant but the easiest way to tell if you have enough air flow is by monitoring how fast the soil dries up. If the soil is taking longer to dry than it should, experiment with improving the air flow to understand if that is the best solution for you to get your plants to dry sooner.
How to improve air flow? You can be creative but here are a couple ideas. Keep the ceiling fan on in the room every once in a while or a window open if it’s warm enough. Keep the plant near a window because the changes in temperature throughout the day will create a light “breeze”. You can also take the plant outside during the warmer months for a few hours during the day so that way it can get some better air flow.
Light influences more than photosynthesis, it can also influence the reproductive growth stage which is the time when the plant is ready to produce flowers, fruits or seeds.
For most plants, you can control growth by manipulating how much light you give your plants. This can be especially important if you are growing vegetables such as lettuce which becomes bitter and edible when it goes into the flowering stage.
How much light do your plants need? Since this is so dependent on individual plants, look specifically for how much your plant needs. Plants will generally fall in this range:
- Direct light: Some plants require hours direct light daily in order to grow strong. This means that the sun is shining right on them, even if it is through a window.
- Indirect light: There are two situations when you want indirect light. The first is when a plant prefers indirect light because they are sensitive to too much direct light. The second situation is when you don’t have access to direct light so you can try increasing how much indirect light you can give the plant so it can grow.
- Low light: And then there are some plants who do well with only a few hours of indirect light a day.
Is indirect light as strong as direct light? Indirect light will usually not be good enough for direct light needs because it does not have the same intensity as direct light. Light coming through windows is already weaker than regular sunlight. Light intensity can also be cut in half even with the plant being moved a couple feet away from the window.
Are grow lights as good as sunlight? Grow lights have been engineered to produce the specific wavelengths of light needed to encourage plant growth. If you are thinking about a grow light, then check out this guide on indoor grow lights.
Remember to read your plants as they will tell you what they need. Are they getting yellow leaves or any burn spots? Maybe try a spot not as close to the window. Are they looking long and leggy? Get them some more light so they don’t continue to grow to reach for the light.
Plants perform best in a stable environment around their ideal growing temperature range. If you let your plants get too hot or too cold, then you risk slowing down their growth or inhibiting their ability to photosynthesize properly which can lead to wilting or a crunchy (dead) plant.
Generally, the best temperature to aim for is one where you are comfortable because most plants can grow in this range. If you are someone who can tolerate snowy weather in a t-shirt and shorts, “comfortable” is around 65-80°F (18-26°C).
Even if this is not the ideal temperature for the plant, it’s going to likely fall within their range so you are happy and your plants are happy. If you have a dedicated growing environment, then you can look specifically for what your plants need. Most houseplants will likely be in the 70-80°F (21-26°C).
Temperature for watering. When you water your plants, use room-temperature water so you don’t shock your plants. Clean out an old jug or get a watering can to make this easier to store water in the room.
Should you keep your plants on a radiator or heat source? Sometimes the best spot in the house (because of light or because you have a cold house) is going to be on a radiator. This is actually ideal for seed starting but if you are growing plants on a heat source, you just need to pay closer attention when watering your plant since the soil will dry out faster.
Most plants need some humidity to survive because dry air causes them to lose moisture that is difficult for them to absorb from their roots alone. Kind of like trying to fill up a leaky bucket.
Humidity is rated from 0% to 100%, with 0 being Arizona during winter and 100 being Florida during summer.
The average house is commonly under 30% humidity, especially during winter, whereas most houseplants thrive above 40%.
How to increase humidity? Besides getting a humidifier, there are ways to slightly increase the humidity around the plant.
- Group your plants together so they have a microclimate around them that supports a higher humidity level.
- Create a pebble tray that encourages water evaporation near the plant. Take a shallow tray and place pebbles in it, then add a small amount of water and set the plant on top of the pebbles.
- If your plant can tolerate misting on the leaves, then mist the leaves periodically. Be careful not to soak the leaves – just a very light spraying is enough to increase the ambient humidity.
Can you have too much humidity? Very high humidity levels for extended periods of time can encourage mold and rot. Your plants are more likely to need higher humidity levels, but if you are increasing humidity past 60% when they don’t need it, then you might run into problems. White mold can develop on your soil or even on the leaves themselves. Pay attention to your plant for mold and if everything is good, then keep on keeping on.
Did you notice all the times I said “it depends on what plant you have”? The best thing you can do is research your specific plant types and take care of them specifically as they prefer. Different plants will have different needs!
Armed with a better understanding of plants in general and what’s important, your thumb is likely growing bright green now. Let us know if you feel better prepared or if you have any more questions.
Author’s Bio: Eric runs Grow For More where he shares how to garden indoors in a sustainable way. When the sun is out, you’ll probably find him outdoors with his fiancée, Kim, and his aussie, Mearle.