Indoor Gardening 

Growing plants on a sunny window ledge or a table in the classroom can be quite simple with the right type of seeds, soil and plenty of light. 

Windowsill gardening without supplemental lighting is a great way to grow herbs (dill, basil, cilantro), microgreens, lettuces, and other short-lived, leafy plants. These plants are small, and reach a harvest size quickly. Growing plants on a windowsill offers a fun way to bring some greenery indoors, explore the process of germination, and taste and smell some of what is grown. 

However, if you want to grow fruiting plants (peppers, peas), larger vegetables, or start seedlings to transplant later into an outdoor garden, we recommend using supplemental grow lights. While it's possible to grow some greens and herbs without lights, plants will have more more vigor with adequate light. 

Regardless of your lighting, review the sections below on soil and containers, plants, and water to learn more about getting started. 

The biggest challenge when growing indoors is sunlight. This is most apparent when starting plants from seed. While a sunny window may provide enough light for a few potted plants, you will likely notice that your plants soon start to appear “leggy,” showing elongated stems as they stretch towards the sun. This is a sure sign that they are not getting enough light. South facing windows generally receive the most sunlight, but they still may not provide enough for your plants, especially if you are trying to start seeds.

With as little as $50, you can set up lights in your classroom to help your plants grow faster and stronger. This article provides a good overview of grow light considerations, and here you can find simple instructions for building a grow light system on wire shelving.

To set up a simple fluorescent or LED grow light apparatus you will need:

• Shop light fixtures: These are the fixtures that hold a 2', 4’  or 8' bulb. Readily available from Home Depot, Lowes, or Amazon. Some fixtures come with the bulbs included, others are sold separately. 

• Fluorescent or LED bulbs: Different bulbs emit different wavelengths of light. Lights that emit the proper light spectrum for plants are readily available as either fluorescent or LED bulbs. Look for bulbs that are specifically designed as “grow lights” to ensure that they emit the wavelengths that plants need. Fluorescent grow lights should have a light rating between 5,600 and 6,400 Kelvin. The easiest thing to do is to look for lights that are marketed specifically as grow lights. Ideally, use high output T5 Bulbs, rather than T12 bulbs.

• A timer: Set the time to ensure that your plants receive approximately 12 hours of light daily.

• A support structure for your light fixtures: This can be metal shelving, PVC piping, milk crates, or a wooden frame. Feel free to get creative, but you will need something from which to hang the light fixtures. You'll want to be able to easily adjust the height of the lights as the plants grow.  Scroll down to the bottom of the page for a design for a simple shelf garden. 

Finally, don’t be afraid to position your lights very close to the growing plants (within 1-2 inches). You can raise the lights up as the plants grow, and it won't hurt the plant if a leaf or two is touching the bulb. 

If you want to learn more about the science behind the lights, this University of MD Extension Blog is a good starting point. 

Heat: While most classroom temperatures are warm enough to easily grow plants, some plants (particularly basil and tomatoes) germinate more quickly and reliably at higher temperatures (75-85). If you feel heat may be limiting germination rates in your classroom, consider using a small electric heat mat to warm your seedlings (Note, these are sold in a variety of shapes and sizes so shop around to find one that fits your needs). 

Soil: Not all bagged soil is the same. It's important to note the intended use of the product on the bag. 

Potting Mix: Soil labeled "potting mix" or "container mix" is best for growing in pots and small containers. Potting mixes are lightweight, and contain either fertilizer or finished compost to provide your plants with nutrients. 

Seed Starting Mix: Bagged mixes that are labeled “seed starting mix” are often meant just for sprouting seeds and do not contain enough nutrients to grow larger plants that will spend their entire life in a container. They are often made primarily of peat or coconut coir. You can start seeds in a potting mix, but it would not be a good idea to try to grow a plant to a harvest size in a seed starting mix. 

Raised Bed Soil: Raised bed soil is generally a mix of compost and topsoil. It's much heavier in weight than potting mix, and can become compacted or waterlogged in small containers. Use this in raised beds, or large containers. You can also mix raised bed soil with peat or coconut coir to make your own potting mix. 

Working with soil: It's generally a best practice to dampen the soil before filling pots to reduce dust and make it easier to work. It can also be difficult for a very dry soil to absorb water at first, so this will better prepare the substrate for starting seeds. 

Compost and Fertilizer: While you won't likely need to add fertilizer or compost for seed sprouting, plants you intend to grow to harvest size will benefit from some additional nutrients. Nitrogen, Phosphorus, and Potassium are the 3 major nutrients all plants need to grow. If you reuse potting soil, grow plants over several years, or grow large plants, the nutrients get used up and you may need to provide more. Adding bagged finished compost or earthworm castings to  your containers can be a great way to augment potting soil you're reusing between plantings, or when transplanting from potting soil to a large pot or raised bed. Plants will often display visible signs of nutrient deficiencies (see this site for images). Yellowing of older plant leaves due to nitrogen deficiency is one of the most common signs.  Most nurseries also carry a wide selection of plant fertilizers, including synthetic products like Miracle Grow, or a variety of organic options (browse a wide variety of offerings on Arbico Organics). Fish and seaweed fertilizers are great organic options to promote all around growth. Alfalfa meal is a good organic amendment to add nitrogen. The ratio on the fertilizer label (e.g. 4-6-2) represents the concentration of Nitrogen:Phosphorous:Potassium (NPK) in the fertilizer. Nitrogen is most essential for leafy growth, while fruiting crops will require more phosphorous to produce fruit. 

Containers: Indoor or outdoor plant containers come in a variety of shapes and materials. The only requirement is that the container have holes in the bottom for drainage. In addition to standard plastic pots and trays, milk cartons, egg crates, plastic take-out containers, yogurt containers and soda bottles can easily be converted into plant containers by poking a few holes in the bottom. In general the container should just be a little bit larger than the root system of the plant. It's more difficult to manage moisture levels in containers that are too large. TIP: Be sure to set a tray under your container to catch the water that drains out. 

Smaller plants with a shallow root system work best for indoor growing. Consider:

• Most leafy greens (arugula, kale, chard, lettuce, mustard, sorrel, mizuna). Grow an assortment to allow students to try different flavors. Note, many classrooms may be a little too warm for spinach, which prefers very cool temperatures.

• Tender herbs such as basil, cilantro, and dill, which are fast growing and flavorful. Many of the savory herbs such as lavender, thyme, parsley, oregano and rosemary adapt well to containers, but are slow growing. If you want to grow these herbs in the classroom we recommend purchasing seedlings rather than starting from seeds.

• Green onions (scallions), or chives.

• Radishes. Radishes come in all shapes, colors and sizes and mature quickly.

• Microgreens. Microgreens are edible "baby" plants that are harvested just after the first true leaves have sprouted. They make a great garnish and a flavorful addition to salads, soups or sandwiches. In the classroom, they are quick to grow, and are a fun way to experiment with flavor, as often the microgreens share some flavors in common with the vegetable they would grow to become (mustard micros are spicy, onion micros taste like onions, beet micros are earthy, etc). 

• Beans and peas. These plants grow quickly, but create long vines that either require support, or should be allowed to hang over the edge of a container or table. Peas are self-fertile and do not require pollinators to form pea pods.

• Nasturtiums and other edible flowers. These are fun and can add color to the classroom.

For established plants: It can be easy to over water plants in containers, resulting in mold or “damping off” (i.e., stem and root rotting) of your young seedlings. Instead of watering daily or weekly, check the soil regularly to see if your plants need water. If the soil is dry an inch below the surface, it is time to water your plants. Small seedlings generally need more regular water than larger plants since their root systems have not as developed. To reduce the chance of mold or mildew growing on the soil surface, try "bottom watering" your plants by adding water to a tray beneath the pot. The soil will wick up the water through the holes in the pot.

For germinating seeds: Plants with small seeds can be particularly sensitive to soil moisture for germination. Unlike when caring for established plants, it's important to keep the seed at the surface of the soil moist (but not sopping wet) until it has sprouted. While it's ok to let the soil surface dry out slightly over the course of a day, when germinating seeds plan for daily watering. A moist paper towel can be placed over the soil surface to help retain moisture over the weekend. 

Indoor gardening often raises questions of how to control and deter pests from the garden. 

Insects: The most common pests in indoor gardens are small insects, such as aphids or spider mites. These insects are often not noticed until you turn over a leaf of your plant, and see it covered with tiny bugs. We recommend using only organic sprays in the school garden and following the application directions on the package. An insecticidal soap can be an effective way to control. Simply fill a spray bottle with dilute soapy water and spray on the insects. It is possible to make your own insecticidal soap or buy a pre-made mix at your garden supply store. Any sort of pest control works best before the pests have become well established. With severe pest infestations, sometimes the best thing to do is to remove the affected plants, and replant. 

Rodents: Provided you grow primarily leafy crops in your indoor garden, you are unlikely to attract rodents with the plants themselves. Ripe fruit such as tomatoes or peppers can attract rodents to the garden, both indoors or out, so be sure to harvest these items quickly when ripe rather than letting them sit on the vine. 

However, mice are very attracted to seeds as a source of food, and particularly love cilantro, chard, beets, brassicas, peppers, squash, cucumbers, spinach, sunflowers, and corn. There are several creative ways to mouse proof your germinating seeds including covering your seeded tray with a plastic humidity dome (like one of these), building a wire cage for your seedlings with 1/4 inch hardware cloth, or putting your seeds on top of a table or shelf, and resting each table leg in a pail of water that the mice can't cross. Closing germinating seedling into a clear plastic bin with a tight fitting lid can work as well. Many seedlings do not need much light until after they have sprouted. The method needed will depend a lot on the determination of the local mouse population. Mice will leave clear evidence behind them if they are eating your seeds: you'll see disturbed soil, and often the empty seed coat left behind. 

While a few seeds are unlikely to attract large numbers of mice, if your classroom already has a problem with mice, it is likely that they will find and eat your seeds. If you start to see evidence of mice around your indoor garden, the best way to control them is to use one of the methods above to exclude them from seeds.

Hydroponics and aquaponics are two forms of indoor agriculture that can be readily adapted to the classroom. Hydroponics is the practice of growing plants in water, with liquid nutrients added directly to the water (instead of getting nutrients by watering plants in nutrient-rich soil). In aquaponic systems plants are also grown in water, and rather than adding liquid nutrients from a bottle, the nutrients are provided by the waste of fish. There are three different techniques for hydroponic or aquaponic growing:

• Nutrient Film Technique: This is a hydroponic technique in which plants grow in tubes, or piping, and a thin trickle of water runs over their roots suppling nutrients.

• Flood and Drain: In these systems, plants grow in gravel or a non-soil media, and water from the nutrient source is periodically flooded and then drained through the plant bed. The drain cycle is essential for suppling oxygen to the plant roots.

• Floating Raft: In this system, plants grow in rafts that float directly on the nutrient rich water. This water is constantly circulated to ensure plenty of oxygen to the plant roots.

There are many creative, fun designs on the web for classroom hydroponic or aquaponic systems. The possibilities are limited only by your imagination. Great Kids Farm offers a simple aquaponics system design as follows:

• The large basin serves as a fish tank (it’s the perfect size for 1 beta fish). 

• The smaller basin sits on top and holds potted plants that are planted in a clay media. 

• A small aquarium pump continuously circulates water from the bottom basin to the top basin, where it returns to the bottom basin through holes in the top tray. This water moves nutrients from the fish waste past the plant roots. 

• If you are interested in requesting an aquaponics kit from Great Kids Farm, please see our kits webpage: http://Bit.ly/GKFkits. 

You can also compost in the classroom using a worm composting system. Worm composting uses red wiggler worms to break down food waste and other organic material into worm castings: the nutrient rich worm “poo” that makes a great fertilizer. Great Kids Farm provides free classroom worm kits for all those interested in keeping worms in the classroom. More information can be found here: http://Bit.ly/GKFkits 

We recommend that in the classroom you limit the “food” you compost in the bin to leafy plant material. Adding fruits such as apples, peppers, or tomatoes can quickly attract classroom pests, such as fruit flies. Thus, the worm compost bin can be a great addition to a school garden to compost all of the old plant material from the garden (rather than food waste).

We encourage you to also consider ways your plantings could connect to school meals. Students may invite cafeteria staff into their classroom to see what’s growing, or try to grow one item they can find on the school lunch menu (even if it’s not the actual student-grown produce that goes onto the lunch line). This can be a fun way to connect gardening with eating, and to build associations between the garden and healthy choices in the cafeteria. Info on school meals, along with current menus, can be found at www.baltimorecityschools.org/meals.