Indoor Gardening 101

Indoor Tomato GardenWhen the winter blahs set in and your dreaming of fresh greens from your summer garden, consider growing indoors. Not only do plants cleanse your household air (read about Greens That Clean) and improve the aesthetics of any indoor space, they can provide your family with a wealth of yummy, organic foods.

City dwellers, or those without a good gardening spot in the yard, may find growing indoors especially useful. Plants don’t need to take up much space — a windowsill is fine if that’s all you have. For others, the indoor garden may become starter plants for an outdoor garden come spring.

Getting Started

An indoor garden can take up as much or as little space as you are willing to give it. Growing plants of all kinds, even tomato gardening can be done on a windowsill or on a table.

Larger growers, or the more dedicated may want to set up a table or bench specifically for the garden. Find an area with a tile or linoleum floor to catch the inevitable drops of water, or place a tarp under your table.

Shelves provide lots of planting room while taking up little space. If using shelves, make sure that adequate light reaches every plant. This may require a separate grow light for each shelf.

Plants need light to photosynthesize and need to photosynthesize to survive. Without adequate light a plant will grow tall and spindly. If there is enough energy to grow leaves, they still may not totally expand. And without enough light, don’t plan on seeing flowers or fruit.

Even plants grown near a window will probably not get enough light during the winter months to thrive. There are a few things to think about when purchasing a grow light.

1.) Plants have photoreceptors that absorb specific wave lengths of light. Your light needs to have the same wave lengths as the sun, which is why a regular light bulb doesn’t work.

2.) The light should be as close to the plant as possible without burning the leaves.

3.) Most vegetables and other plants do best with 14-16 hours of sunlight or simulated light. There are a few ways you can tell if your plant is getting enough light or not. If it isn’t getting enough light, it usually will have small leaves, thin stems, and the color of the plant will be lighter than usual.

4.) A hormone called “florigen” controls budding and flowering. Long day plants require about 14 to 18 hours of light to produce just the right amount of florigen to flower and reproduce. Short day plants require about 10-13 hours of light. If short day plants are exposed to too many hours of light, florigen can be destroyed, preventing blooming.

Selecting a Grow Light

There are a lot of different grow lights out there and it can be confusing to figure out which type is best for your indoor garden. The following run-down should bring some clarity.

Incandescent Lamps are inexpensive and can be bought at a hardware store or nursery. While they work OK for growing houseplants, they are not ideal for an indoor garden.

Fluorescent Lights work best for growing herbs and other plants that don’t require a lot of light. They are not good for plants that are budding or flowering because they don’t put off enough light. Inexpensive, they can be purchased at the local hardware or garden supply store.

The new “Compact Fluorescent Systems”, however, are quite bright and efficient and in some cases might even be better than the fancier high intensity discharge (HID) lights. Compact fluorescents are smaller and more efficient than older forms of fluorescent lighting so they can be used for all plants. They also produce less heat than incandescent and HID lights and consequently can be placed much closer to the plant.

High Intensity Discharge (HID) Bulbs are the brightest and most efficient lights available, but they can be expensive. One 1,000 watt grow light bulb can produce the same amount of light as 50 40-watt fluorescent lights.

There are several types of HID bulbs:

• High Pressure Sodium
• Metal Halide
• Low Pressure Sodium
• Mercury Vapor

The High Pressure Sodium and Metal Halide bulbs are the only ones indoor gardeners will need.

High Pressure Sodium (HPS) Bulbs produce a red-orange light that benefits flowering. With an average lifespan 2X that of metal halides, high pressure sodium lamps are economical. This isn’t a great light if you are only going to use one, as it doesn’t produce light in the blue spectrum needed for leafy growth.

Metal Halide (MH) Bulbs produce a blue-white color that is conducive to encouraging leafy growth and keeps plants compact. A bulb will last about 10,000 hours and produce up to 125 lumens per watt compared to 39 lumens per watt for standard fluorescent lights and 18 lumens per watt for standard incandescent bulbs. This is a good light to start plants out with. When it comes time to flower, switch to a High Pressure Sodium bulb.

There is more to a grow light than just the bulb. You can purchase the reflector, cord, ballast, bulb and other parts separately, or buy a whole system that just needs to be plugged in.

What size grow light do you need? This will vary depending on the mounting height of the reflector (how far above your plants the light is) and the size of your indoor garden. In general, the following recommendations apply:

Size of Light
Area Coverage
Mounting Height
Above Plants
400 Watt no outside light
some sunlight
5′ x 5′ area
8′ x 8′ area
1 to 4 Feet
600 Watt no outside light
some sunlight
7′ x 7′ area
10′ x 10′ area
1.5 to 5 Feet
1000 Watt no outside light
some sunlight
8′ x 8′ area
12′ x 12′ area
2 to 6 Feet


Temperatures of 65-75°F are best for most plants. A variance of 10°F either way will probably be OK. Plants that are too hot will be small and weak. Plants grown at too-cold temperatures may have yellow leaves that fall off.


A lack of humidity in the house can be a challenge for indoor gardeners. Winter tends to be drier than summer, and if you run the heat in your house the problem is further compounded.

You know you have a low-humidity problem if:

1.) The tips of your leaves are turning brown
2.) Plants look withered or puckered
3.) Plants lose their leaves
4.) You’ve researched how much humidity your particular plant needs and it isn’t getting it.

To increase humidity:

• Mist plants daily, or more often as needed. (Do not do this with hairy-leaved plants since the water hangs around longer and could cause disease.)
• Place a tray of water near your garden (don’t put plants in the tray, this can lead to other problems). Fill the tray with lava rocks to increase surface area for evaporation.
• Place plants close together to create a microenvironment with a higher relative humidity.
• Run a humidifier (this might benefit your skin as well!).
• Purchase a humidity controller, which can humidify or dehumidify depending on your needs.

Growing Medium

Indoor gardens benefit from a good planting medium — soil found outside is not appropriate, since it’s often too heavy and may contain weed seeds and insect pests. Instead look for a mix that is specific to indoor plants. A good growing media should remain loose and drain well, yet contain enough organic matter to hold nutrients and moisture.

Most commercial organic mixes will work well, or you can create your own (see Potting Mixes for Certified Organic Production).

Tip: Ocean Forest Potting Soil (shown here) is a quality blend of premium earthworm castings, bat guano, and Pacific Northwest sea-going fish and crab meal. Composted forest humus, sandy loam, and sphagnum peat moss are added to provide a light, aerated texture. It’s perfect for containers and ready to use right out of the bag.


Instead of growing indoor plants in a soil mixture, you may want to try out hydroponics. Basically, this means gardening without soil. Soil holds nutrients and anchors plants roots. When growing hydroponically you provide the nutrients directly. Instead of being bound up in soil, the nutrients are readily available to the plants.

Some of the advantages of growing hydroponically include:

• Faster plant growth (up to 50% faster) since plants can easily access water and food.
• Roots grow throughout the media without becoming root bound, so containers can be smaller.
• Plants start in a disease-free medium and are less likely to become infected.
• If plants do become sick, the disease is usually in one plant, not all of them.
• Plants droop before they wilt, so you’ll know to water them before they are damaged.

Check out the Hydroponics Glossary at Hydrofarm is the nation’s oldest and largest manufacturer of hydroponics equipment and grow lights. We offer many of their products here at Planet Natural.

Choosing plants

Almost anything can be grown indoors — as long as it eventually doesn’t get too big. However, do consider growing plants with similar light, humidity and watering needs together. Some obvious choices for an indoor garden include:

Salad Greens
Tomatoes, especially cherry types
Beans, Bush
Shasta Daisy
Apples, dwarf varieties

Don’t stop there, as mentioned above, almost anything can be grown indoors in a container.

Plants can be grown from seed (started inside and staying inside) or they can be transplanted from your outdoor garden at the end of the season. Plants will need to be acclimated before bringing them in the house and again when you put them outside in the spring or fall.

Moving Plants Outside

Plants and seedling grown inside need a period of “hardening off” before they can permanently live outdoors. The hardening off process gives them time to develop a thicker cuticle and avoid water loss while being better able to withstand the harshness of weather. The following steps will help acclimate indoor plants to life in the great outdoors.

1.) 7-10 days before you want to transplant your plants, place them outside in a shady spot or cold frame for 3-4 hours.

2.) Each day, increase the time spent outdoors by 1-2 hours. Bring plants back in each night.

3.) After 2-3 days, place plants in morning sun, then move them into the shade in the afternoon.

4.) If the temperature stays around 50°F, plants should be able to stay out all day and night after 7 days.

5.) In about 7-10 days transplant your seedlings or plants. If possible, transplant on a cloudy day and water thoroughly.

To acclimate plants by withholding water or by using a cold frame, read How to Harden Off Plants.

Moving Plants Inside

At the end of the growing season you may want to move plants inside to your indoor garden. After potting these plants (if they are not already in containers) they will need a period of acclimation, just as plants going the other direction do.


Plants grown in containers dry out more quickly than their soil-grown counterparts and require frequent watering. Always use room-temperature water and add enough water that it runs through the drain holes of your pot or container (do not let water collect in a saucer or under the plant — this can lead to rot or disease).

Use your finger to feel the soil or use a moisture meter to be sure you are not over or under watering plants.

Signs of Over Watering Signs of Under Watering
Wilting from stem towards leaves Wilts along the outer tips of the leaves first
Lower leaves dropping Dry soil
Discoloration Brown edges along the leaves
Plant might stop growing Wilting foliage
Wilting foliage Leaves or flowers drop prematurely

Do you have a hard time remembering to water the plants? Read How To Make a Self Watering Garden or How to Make a Self-Watering Seed Starter in Ten Minutes to learn how to start a garden that water’s itself.

Fertilizer/ Nutrients
Plants grown indoors will need an extra boost of nutrients or fertilizer since most of the nutrients in the soil or growing medium are quickly taken up by the plants or leached out during watering.

Organic fertilizers and hydroponic nutrients for indoor plants abound. Follow the instructions on the package for how much to use and how often to fertilize.

If you compost at home, you can make a compost tea to water your indoor plants. Here’s how:

1.) Fill a bucket about 1/3 full with finished compost.

2.) Add water until the bucket is full.

3.) Let the bucket sit for a few hours, if not three or four days (don’t let it freeze!).

4.) Using cheesecloth or a fine screen, strain the mixture into another container. (Anything leftover can be thrown into the garden or back into the compost bin.)

5.) Add water to the liquid until it is the color of weak tea.

6.) Apply the compost tea to the soil around your plants.


Growing Indoor Plants with Success (PDF) – To be a successful indoor gardener, you need to understand how the interior environment affects plant growth and how cultivation differs from growing plants outdoors (University of Georgia Cooperative Extension).

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