Planters are the closest simulation to the natural growing environment for indoor plants. Properly designed and installed planter beds can thrive and grow for decades. Here are some considerations when designing and specifying planter beds and atriums:
Planter bed size
Depth: Planters must be deep enough to accommodate the root ball of the desired size of plant material (see chart below for recommended depths).
Indoor soil is very loose and does not mound like topsoil, so the correct depth is important to cover plants roots. If not deep enough, smaller plants will need to be used.
If the planter is too deep for plant material, extra potting medium will need to be used (at some expense) and this additional volume of soil will have more compacting and shrinkage over time.
|Size of Plant Material||Planter Depth|
|ground cover, 1′ tall plants||8-12″|
|2′-6′ tall plants||14-18″|
|7′-12′ tall plants||24″|
|12′-24′ tall plants||36″|
| 24’+ tall plants||48″ (usually maximum depth needed)|
Width: For small planters, the width of the planter needs to be equal to or larger than the depth. For example, a square planter for a 10′ tree should be at least 24” wide and 24” deep. See also decorative container size chart for sizing for planters for single plants. A long planter to be filled with vines could be 8” wide by 8” deep, and as long as you desire.
Preparation for planting
Design beds need to be sealed off from exterior environment. It is not advisable to plant directly over exterior soil without protective barrier (e.g. liner and insulation). Drains are not needed, since a layer of drainage material in the planting area provides a controlled reservoir of water below the plants’ roots that indoor plants actually prefer.
We recommend waterproof lining of all planters to prevent moisture from seeping out or leeching as well as cold encroachment from concrete or metal. If planter is near an exterior wall or built directly over the ground, we highly recommend insulating the bed. Cold encroachment can occur even with exterior retaining walls down 6 feet below the ground along building sides. Cold soil zone can cause significant damage to plants, including widespread disease and die-off. Once soil is contaminated with disease, it is difficult to keep new plants healthy. Construction insulation (R=5 or greater) can be used on the bottom and sides of planters to reduce cold damage. The price of the insulation is small compared to potential future problems.
Botanicus recommends direct potting of plants into planter beds. A major benefit is improved health and growth because plants’ roots have room to grow, and they experience less changes in moisture range (due to larger soil volume). A more attractive foliage design can be used, and ground cover plants are able to grow into a carpet of foliage. Watering is streamlined and more accurate, since all plants share a common soil volume from which to absorb moisture. With this method, beds are lined with a 2-8” layer of course drainage material (such as sterile crushed stone or perlite) and the filled with potting medium.
We recommend a soil medium composed of mostly spaghum peat moss with some perlite for aeration. This is a sterile, highly absorbent mixture that can provide even moisture and maximum root growth. A 2-4” layer of material such as sterile crushed stone or perlite below the soil medium provides for good drainage. Avoid heavier mixtures or exterior grade “topsoil,” this compacts and suffocates roots of tropical (indoor) plants. Their are several available mixes specially blended for interior landscaping use (e.g. Metro Mix, Promix, Fafard.)
By direct planting into planters you can skip the use of bark chips to fill the planter. Top dressings such as bark chips or spanish moss can encourage disease and fungus, host annoying gnats, change pH over time, and make checking soil moisture more difficult. In addition, we do not recommend using top dressings because they significantly reduce the plant’s ability to clean the air.
Since planter beds hold a large volume of soil, they also require significant water. We recommend installing an adjustable hot & cold running water source (preferably hose spigot) near beds for easier watering. If a mixture unit is not possible, sometimes bringing pre-mixed warm water (temperature above 70 degrees) directly to hose spigot is possible and less costly. Cold water can stunt and damage plants, as the water temperature can be 40 degrees F in winter. Also consider safety and possible leakage ramifications when deciding water source placement (e.g. hoses stretching across walkways can be very hazardous). Consider including a irrigation system in the design, similar to golf courses or like outdoor landscaping contractors provide.
Light & Skylights
All plants require different amounts of light to photosynthesize (manufacture food) and grow. Quantity and quality of light available indoors is significantly less than light in nature. Window size, distance from the window (to the side or under), the presence of curtains or shades, partial obstructions (awnings, overhangs, trees, etc.) influence the amount of light the area receives. Our light code is a guide for your plants, and should be adjusted to seasonal variations and individual locations. In WNY, it is unlikely that any plant indoors will get too much light, so plants in the lower light categories will grow in many higher light areas (although they may need more additional care).
- Low light: under a bright fluorescent fixture, at least 50-100 footcandles measured at desk height
- Medium light: near windows (2-4 feet back or set to side of South, West, East window) 100-250 footcandles
- High light: directly in front of a window (without blinds, shading or overhangs) over 250 footcandles. Other High light plants:
- Giant Plants: Trees and palms up to 30’L
These light intensity categories are based upon duration of 10-12 hours per day minimum of 5 days per week. Lower duration of light requires higher intensity for plants to live.
Skylights provide natural light which is ideal to sustain large foliage plantings. Plan for angle and placement of windows and skylights to provide as much direct sunlight as possible. Many large foliage plants require up to 6 hours of direct, unfiltered sunlight to sustain growth. Light shines downward, but only penetrates at an angle of 30-45 degrees. This means that a skylight in the middle of an atrium may not shine onto planters at the edge of the room. The angle of light changes drastically on a seasonal basis (as shown in photo to left).
The following changes the amount of light that reaches the plants:
- Height of roof and distance to travel to leaves (light at 20′ above floor is 2x light at 10′)
- Smaller width of skylight (if narrow, light may only shine in from 11am to 1pm)
- Glazing, tinting, and use of opaque materials instead of clear glass (can reduce up to 90% of sunlight)
- Direction & angle of skylights – light sweeps from east to west, shining below on the opposite side of the skylight; north side has no direct light, south has bright ambient light.
Temperature & HVAC
Tropical plants need a sustained environment of 60 to 90 degrees Fahrenheit. Only a few plants can tolerate dips below 50 degrees without major systematic damage. Even a few seconds of cold air (from an open door for example) can damage a tropical plant. For example, Peace Lilies, Ficus, and Dracaena leaves turn black even with brief exposure. Dips below 60 degrees will cause Ficus to lose leaves, and other plants turn yellow. Exposure to cold air can reduce water usage, allow fungus to spread and rot the roots, or cause foliage spots. Exposure to very hot temperatures causes some plants to wilt, others to lose leaves. Water usage is also dramatically increased in high temperatures. Wilting a plant can cause systematic damage, with symptoms similar to cold damage.
Heating and cooling systems should provide a constant temperature of 60-80 degrees Fahrenheit. Large skylights and southern-facing window walls can naturally warm the space (the “greenhouse effect”) to high temperatures even during winter. (Consider the heat burden during the air-conditioning season.) Heat rises and will accumulate dramatically at the top of atriums if not circulated (e.g. ceiling fans.)
Continual air movement is important to simulate a natural environment. The ideal humidity range is 40-80%, but keep in mind that foliage plants add 10-30% to the humidity level, depending on their rate of transpiration and the temperature. If system does not remove moisture, condensation could accumulate on glass and plant leaves.