Potting a spider plant shoot.
In addition to the requirements listed in What Does My Plant Need?, an indoor plant typically needs a pot and potting soil for its roots. Selection of the type and size of the pot, and the kind of potting soil can have a major influence on the success or failure of the plant.
Never use field or garden soil in a container. Always use a potting soil developed for plants growing in containers. Potting soil or growing media must be of good quality and meet certain performance criteria. To sustain plant growth, the medium must hold large quantities of water in a limited volume and yet maintain a high volume of aeration. Because soil in a container does not behave the same as soil in the field, potting soils are typically formulated with a high percentage of bulky organic materials such as bark, wood chips, peat, or compost. It is more practical to use a commercially prepared potting soil than to buy ingredients and formulate your own.
The following recommendations help ensure successful potting. Select mixes high in bark, forest materials, or sphagnum peat with vermiculite (pdf) or perlite. Thoroughly leach any potting soil before placing seed or plant material in the mix. Leaching will reduce soluble salts to acceptable levels in most mixes. Fertilize with a soluble fertilizer according to the manufacturer’s directions within 2 weeks after plants are growing in new potting soil to replace leached nutrients and those taken up by the plants.
Container size and type
A container should be large enough to provide room for soil and roots, have sufficient headroom for proper watering, and provide good bottom drainage. (Headroom is the amount of space between the soil level and the top of the pot that allows for watering a plant).
Clay and Ceramic Containers. Clay pots, unlike plastic ones, absorb and lose moisture through their walls. The greatest accumulation of roots in any container is frequently next to the walls of the pot. Ceramic pots are sometimes glazed on both the outside and inside. Frequently, they are designed without adequate drainage holes. Use them only as a decorative sleeve to hide a well-drained but unattractive container.
Actively growing indoor plants require occasional repotting. Slowly growing plants only rarely require repotting. The pot selected for repotting should have a diameter no more than about 2 inches (5 cm) larger than the pot in which the plant is currently growing. It should also have a minimum of one drainage hole and be clean. Wash soluble salts from clay pots with water and a scrub brush. Wash all pots in a solution of one part liquid bleach to nine parts water.
Before repotting begins, the medium should be moistened. If the plant has become root-bound (pdf), cut any roots that encircle the plant; otherwise, the roots will never develop normally. If the soil surface has accumulated salts, remove them. Set the root ball in the middle of the new container and fill soil under the root ball and around the sides between the root ball and pot. Placing gravel or other coarse-textured material in the bottom of the pot does not improve drainage. In fact, it will usually impede drainage, which can result in root disease. Do not pack the soil. To firm or settle it, tap the pot against a table top or gently press the soil with your fingers.
After watering and settling, the soil level should be sufficiently below the level of the pot to leave headroom for watering. A guideline is to leave about 1 inch (2.5 cm) of headroom in a 6-inch (15-cm) pot and proportionately more or less for other pot sizes.
Plastic and Fiberglass Containers. Plastic and fiberglass containers are usually quite light and easy to handle. They have become the standard in recent years because they are relatively inexpensive and can be made quite attractive in shape and color. Plastic pots are easy to sterilize or clean for reuse, and because they are not as porous as clay pots, they need less frequent watering and tend to accumulate fewer salts.
The following recommendations help ensure successful potting. Select mixes high in bark, forest materials, or sphagnum peat with vermiculite or perlite. Thoroughly leach any potting soil before placing seed or plant material in the mix. Leaching will reduce soluble salts to acceptable levels in most mixes. Fertilize with a soluble fertilizer according to the manufacturer’s directions within 2 weeks after plants are growing in new potting soil to replace leached nutrients and those taken up by the plants.
Plants for specific indoor gardening uses, Table 11.3 (pdf) in California Master Gardener Handbook. UC. Buy Publication