Introduction

When an ornamental crop is ready for sale (finish time) is the result of many interconnected factors. The theoretical optimal finish time is often not reached, as weather conditions, insects, diseases, and other factors that are not within the grower’s control can influence the rate of plant development.  

Top growers have highly advanced greenhouses, with many automated systems to maximize production. Mid-size and small operations may not rely as much on automation, using hand-watering, and less sophisticated chemical application methods.  

Connecticut has a robust greenhouse industry, with over $193 million in sales annually. Bedding plants are an important category, and bring in significant revenue for greenhouse operations each Spring.  

Most bedding plants are started from plugs or rooted cuttings and have a rapid turnaround time in the greenhouse. There are many factors that allow for the production of high quality bedding plants, that include cultivar selection, fertilizer, temperature, and control of pests and diseases.  

Growers need to accurately time plantings to meet contract obligations and customer schedules. The data shown below is for finish times of common bedding and garden plants grown in Connecticut. 

Factors That Affect Finishing Time

Cultivar

Cultivar selection is based on experience, cost, and availability. Some crops have specific temperature, water, and light requirements for growth and development. These crops have been developed for production at specific times of year.  

There are many cultivars of the main bedding plants available. Most seed varieties are F1 hybrids and are typically more expensive than open pollinated varieties.  

Some crops are available as vegetative cuttings only, and may be proprietary. Cultivars that are hybrid should be selected based on their characteristics, and productivity in the region. Varieties that are slower growing should be carefully considered before planting on a large scale. 

Planting method and establishment

Most bedding plants are grown from plugs, ready to transplant upon purchase from a specialty plug producer. Some growers grow their own plugs from unrooted cuttings. Direct seeding is occasionally used for difficult to find varieties, or based on experience.  

Workers transplant the plugs directly into flats or pots. In larger greenhouses these steps are automated, with conveyors automatically moving the plant material to the correct area of the greenhouse.  

Labor and mechanization are considered part of the production process. As there are numerous steps where bedding plants are handled, each of these steps can influence the final plant if not done correctly. Bedding plants are planted densely to maximize space in the greenhouse. 

Container size can affect finish time, with larger pots taking longer to fill out. Bedding plants are often produced in flats. The 11 × 21 in. flat, or 1020 flat, is the industry standard, with various insert containers such as 804 and 806 packs, or 12-packs.  

However, there are many flat and pot sizes, and the selected size may be determined by the requirements of the market or customer. Hanging baskets are very popular but require a longer lead time to sales. 

Weather

Greenhouses provide significant protection from variations in weather, which is the least controllable factor affecting finish times. Excessive cloud cover and rain can lead to slower growth, and increases in certain diseases such as gray mold. Many technologies used in greenhouses are designed to modify the effects of adverse weather. 

Temperature

The growing temperature plays an essential role in crop quality and time to finish. Generally, higher temperatures equals faster growth. However, some crops produce the best quality at low temperature ranges. For example, snapdragons and pansies are cool temperature crops. Day and nighttime temperatures will influence crop growth and flowering time.  

Light

The science of plant lighting continues to advance. Both light intensity and photoperiod influence plant growth. There are many lighting fixtures available for growers that aim to improve flowering or other aspects of plant growth. High pressure sodium lamps, metal halide lamps, LED, and other lighting systems offers unique advantages and provide the plant with specific light wavelengths. Recent advances allow growers to control mols/day of photons. 

The material used in covering the greenhouse can influence the amount of available natural light. Structures include glass houses, polycarbonate, and acrylic. Many growers use high tunnels covered by polyethylene plastic film. Shading is accomplished with retractable shade cloth or shade paint. Each structure has specific attributes beneficial in production of certain crops. The material of the structure can have a small impact on finishing times, as light may be unevenly distributed if the glass or plastic is dirty and opaque. 

Plant growth regulating (PGRs) chemicals

In addition to modifying temperature and water, plant growth regulating chemicals (PGRs) are used to reduce the height and internodal spread of bedding plants. B-Nine, Bonzi, and Cycocel are some of the most commonly used PGRs, and can be applied as a drench or spray.  

These chemicals are applied at the labeled rate to reduce growth and shorten internodes. Most bedding plants receive two or more applications of PGR during production. A compact growth habit is often most attractive to retail plant buyers.   

Disease and insects

Plant pathogens can cause significant losses in bedding plant production. Some diseases are constantly present in the greenhouse and will infect when conditions are favorable.  

Botrytis blight is widespread and frequently observed infecting a wide range of bedding plants. Fungicides are necessary to protect plants against this pathogen. Pythium and Phytophthora root rot can cause significant losses if left untreated, and spread with splashing water. Leaf spot diseases and powdery mildew are generally less of an issue during bedding plant production than in the landscape.  

Bacteria are common on seedlings, as they can be seedborne, and spread when conditions are warm and humid during propagation. 

Insects that affect bedding plants cause physical damage, and can transmit viruses. Thrips, fungus gnats, whiteflies, aphids, and spider mites are the most frequently observed insect pests of bedding plants.  

Thrips and aphids are especially problematic due to insecticide resistance, and the ability to transmit viruses. Insecticide application, monitoring, and integrated pest management techniques are used to combat these pests. There are relatively few bedding plants with resistance to diseases and insects due to the diversity of available crops.

Media and fertilizer

Many soilless media types are available commercially. Most growers no longer use soil in production of bedding and garden plants. Soilless mixes often contain peat moss and are light weight with high water holding capacity. Media that contains Hydrafiber tends to dry unevenly, but is used by some operations as an alternative to peat.  

Media pH can have a direct effect on the availability of nutrients. For example, iron and magnesium may become toxic at high media pH but be severely limited at low pH’s.  

Plants grown at an incorrect pH will not respond as well to additional fertilizer as plants grown at the correct pH. Water pH can also have an effect on nutrient availability.  

The amount and type of fertilizer used is very important to maximize finish times. Even a slight nutritional deficiency can slow down finishing times. Applying excess fertilizer usually will not increase crop growth, or may result in overly vegetative plants with reduced flowering.

Irrigation

Having the correct irrigation schedule is very important in the production of bedding plants. Small and delicate plugs can desiccate if not watered at the correct time on hot days. Watering for bedding plants is usually overhead, based on grower experience and the effect of sunlight, temperature, and cultivar.  

Modern potting media is porous and overwatering is generally not an issue unless there are long periods of cloudiness and cool temperatures. Well water is preferred over surface water, and large greenhouses usually have precise control over water hardness and pH. 

Other cultural factors

The age of planting material can influence the growth of the crop. This is a stage that is often out of the growers control, as plugs are purchased from specialized greenhouses. Planting material that has received excess PGR, or has been held for too long may take longer to develop new roots, or grow abnormally. 

Postharvest

Postharvest transport and handling is one of the most important stages of crop production and usually the one where major losses can occur. Growers cannot control much of the postharvest process, including handling, conditions on the truck, and watering once plants are at the market.  

Bedding plants are usually not shipped excessive distances, and are ready for sale as soon as they are transported to market.   

Extended periods in a humid truck can lead to losses from Botrytis blight and other diseases. The saleable bedding plant should be green, healthy with robust plants, and free from pests and diseases. Flowers are not always required but will increase the likelihood of sales. 

Finishing times

The data in Table 1 are based on information from the Connecticut Department of Agriculture, University of Connecticut, and seed companies. If specific crop information for Connecticut was not available, sources from the Northeast US region were consulted. The times listed are for saleable bedding plant packs. Three figures are given for each crop: slow, good, and excellent finish times.  

Slow finish times are the slowest times that growers should expect, in years, with adverse conditions. Growers may not be able to meet contract obligations with these times. 

Good finish times are average for experienced growers. Crop culture recommendations are often based on this production level. These finish times should be attainable in most years, unless adverse growing conditions cause significant reductions in growth. 

Excellent finish times are attained by experienced growers growing their crop under optimal conditions. These times are a result of favorable weather, adequate fertilizer, insect and disease control, and the attention to detail of the grower. 

Table 1: Finish times for common bedding plants grown in Connecticut. Saleable bedding plants of high quality. 

¹Finish time from transplant of plug in packs or 4’ pots.  

²Time from seed.  

³Cockscomb type. 

Table 2: Finish times for common perennial-type bedding plants grown in Connecticut. 

¹Finish time from transplant of bulb or liner in 4’ pots.  

²Time from seed.  

Acknowledgement

This work is supported by the Crop Protection and Pest Management Program [grant no. 2021-70006-35582] from the USDA National Institute of Food and Agriculture.