Whether you have a home greenhouse or are selecting pots for a commercial greenhouse that produces seedlings for retail sale, selecting the right pot is important to the success of your greenhouse gardening. Although clay pots can work as well in a greenhouse, as in any other location, most greenhouse plants are first grown in a special, temporary pot before being transplanted to their final location. Understanding the different pots will help you select the right pot for your purposes.
Injection-molded plastic pots are, according to Washington State University, the predominant pot in the greenhouse industry. These pots are made from polyethylene, polypropylene or polystyrene resins. These pots are thinner than the blow molded pots used in nurseries for outdoor tree and plant growth. The lighter weight injection-molded pots use less plastic, while being strong enough to ship to end consumers. The thin sides of these plastic pots also give a little if the roots begin to outgrow the container, as can happen if a retail plant sits longer before being bought and planted in a home garden.
Peat pots are a more environmentally friendly alternative to plastic pots. In many cases, peat pots can be used in a greenhouse as a direct replacement for plastic pots. An advantage of peat pots over plastic pots is that the peat pots can be directly planted in a larger pot or in your garden. Peat pots supply organic nutrients to the plant as it grows. As you water the plant after re-planting, the water will cause the pot to dissolve in the soil. Peat pots are available in a variety of thicknesses. For starting home seedlings, a thinner pot may work. For commercial use, a thicker pot may stand up better to shipping. Be careful of over-watering when using peat pots. Too much water can cause the pot to degrade. Unfortunately, peat is a somewhat limited resource.
Another biodegradable alternative for greenhouse planting are fiber pots. Fiber pots can be made from wood fiber or, in some newer natural pots, coconut coir. Fiber pots are often coated on the inside with water-based coating to help maintain stability during shipping and seedling growth. However, uncoated pots often have healthier root systems than coated or plastic pots. This increase in root health is due to increased air transfer through the sides of the pot. Because of decreasing availability of peat, many organizations, such as the Royal Horticultural Society in the United Kingdom, are transitioning away from peat to other forms of fiber-based pots and growing media.