Containers

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Container Basics

Container type, size and shape

Bigger is better? 

One of the biggest limitations to container quality is water. Particularly with large plants. 

A good size container plant can easily use an inch or more water each day in the summer. A large deep container may be able to hold enough water to supply the plant for 3 or 4 days but a shallow container may only hold enough water for 1 or maybe even only 1/2 days when it is hot and dry and windy. Unless there is an irrigation system plants can easily use all the stored water in the container in one to several days.

Typical rains during the summer are not enough to refill the container so plant stress will rapidly cause wilting or death.

If you fill a 10 inch hanging basket with media and then dump it out - 

The same media will fill 2 - 8 inch baskets and more than 6 - 6” baskets. 

It is easy to see why the same size plant in a 8 inch basket needs to be watered 2x as often and in a 6 inch basket as much as 5-6 times as often as the 10 inch basket.


Media

Media functions to:

  1. Support the plant
  2. Hold water for the plant
  3. Provide air to the roots
  4. Hold and provide nutrients

A good medium should be:

  • Well drained with good water holding capacity to provide air and water to the roots
  • Have good nutrient holding capacity (CEC)
  • Be weed and pathogen free


Media components at Frey Brothers, A Pa based media manufacturer

Typical components of a greenhouse or nursery media include peat moss, pine or hardwood bark, coir (coconut fiber) or other bulk composted organic material. These materials make up the majority of the media. They are selected based on cost and availability.  

A desirable organic component will be stable for several years, that is it will not rapidly decompose. However, in a warm moist environment it is not uncommon for media to shrink 1 to 2 inches in a year. A large outdoor container may need to have media added every year before planting.

Vermiculite or perlite are often added to improve drainage and various fertilizers, wetting agents and biocontrol agents may also be added. 

Soil is seldom used except in large outdoor containers because it is difficult to find a good quality soil without herbicide residue and soil holds too much water in shallow or small containers. When soil is used it is often mixed with a commercial growing medium to improve aeration and drainage.

Product information can be easily found on the web. For example click on the link below:

Griffin Supply provides media for many commercial growers in the NE


Plant production and landscape environment - Temperature, Light, Humidity and Water

Production temperature depends on the crops grown. Many container plants are tropical or warm season annuals and thus are grown in a greenhouse at relatively warm temperatures 68F and greater. 

Some of our container plants are herbaceous perennials and may be grown at cooler temperatures or outdoors. 

Plants that have been grown in a greenhouse should be acclimated to outdoor conditions in the spring before planting. 

In frost prone regions care must be taken not to plant tropical container plants too early. Some tropical plants may be brought in to overwinter in cold environments. 


Typical examples include Canna, Alocasia (pictured above), and Caladium. 

The edges of containers that are exposed to sun may heat up considerably limiting root growth or damaging tissues.

Low light decreases flowering in most plants. A sun loving container grown plant that is placed in low light may stretch and not flower adequately. 

Select shade loving plants for low light containers.

For bright sunny dry locations drought tolerant succulent species would be appropriate selections

Salvia is stressed and stunted near the tree in this planter

Watering can be a challenge for containers in production or in the landscape. Water stress may cause stunting or leaf edge burn, or outright death. 

High salts in irrigation water can contribute to leaf yellowing. Highly alkaline water can raise media pH and limit availability of iron and other nutrients causing leaf yellowing or interveinal chlorosis. This is common in some container grown plants like Calibrachoa.

The calibrachoa in the photo above is displaying leaf yellowing from iorn chlorosis. Calibrachoa in containers may need to have supplimental iron fertilizer applied during the growing season.

High humidity and saturated soils in production or in the field can lead to disease problems in container plants. Typical disease problems include Botrytris, Powdery Mildew, Downey Mildew, Pythium, Rhizoctonia.

Many annuals and perennials used in containers have high fertility requirements. Containers have limited volumes and limited CEC, thus have limited ability to store plant nutrients and can become depleted. Leaching of nutrients from containers can be a problem in wet years and additional fertilization may be required. Slow release fertilizers are often used in landscape containers.

Container design and plant selection:

Containers should be planted with species and cultivars with similar cultural requirements. 

For example a sun loving plant like a Petunia is usually a poor planting companion for Impatiens. 

This container demonstrates a common design practice in containers which is to use 3 types of plants

  1. a “Thriller” in the middle
  2. a “Filler” surrounding the thriller
  3. a “Spiller” to trail down the sides of the container

In addition it is important to consider vigor and only plant species and cultivars with similar vigor under the growing conditions of the container, otherwise one species or another will ultimately dominate the container. 

Bloom time is another consideration. Plants should have similar or complimentary bloom times. 

Always consider what the container will look like at the end of the season as well as during its peak. 

The number of plants used depends on the size of the container. Consider the mature size of the plants when specifying plant lists or planting a container. For example 3 - 5 plugs may be a good number for a 10” hanging basket. A 4 foot wide street container may require 10 - 30 plants depending on the species selection and cultivars used. 

A good example is petunia. Many of the vegetatively propagated cultivars can spread to fill a container planted on 18” centers. Most of the seed propagated petunia cultivars will not fill if planted on greater than 8-10” centers. Consider also how long a client is willing to wait to have a full container. 

Many plant suppliers provide mixed container advice for growers and landscapers. For example Proven Winners provides a lot of container examples on their website. Use the link below to see some of the PW combinations

Proven Winners container recipes

Other suppliers also provide information and plant trial information is also available from a 

variety of sources. 

At the Penn State variety trials in Landisville Pa. we evaluate new and outstanding cultivars of annual plants in containers. Each year we evaluate 1000-1500 cultivars. Trials like ours are conducted in many locations across the US and are a great place to see new plants and to see how they will perform in your area. The link below will take you to the PSU variety trial website.

Penn State Variety Trials

Common disease problems in containers and container grown plants:

Information on these diseases can be obtained from many online sources. Follow the links provided to learn more about each problem. Click on the name of the pathogen.

Botrytris: Grey mold - common everywhere, grows on all plant parts but is most common on old flowers, dead leaves, and leaves in contact with the soil. Can cause rots of flowers like marigold and Pelargonium.

Powdery mildewCommon in the fall on many container plants and also in the greenhouse particularly on some hanging baskets. Mildew can be fairly host specific, resulting in a white powdery appearance to the upper leaves.



Downy mildew: White or red, mostly on the underside of the leaves. This has recently become a major problem with Impatiens. Click on the following link for more information about this problem on Impatiens. Impatiens mildew

Pythium: Common root rot in containers. 

Thielaviopsis: Commonly causes stunting in container grown plants


Exercise:

Follow the link below to the container design assignment and turn in your submissions to the drop box in the Week 9 Canvas module

Container design assignment

© Penn State Horticulture  2019