Commercial Greenhouse Production

Scientific Name: Pelargonium hortorum

Common Name: Zonal geranium

Family: Geraniaceae

Dr. J. Raymond Kessler, Jr.

Auburn University


The exact origin of Pelargonium hortorum is unknown, but probably resulted for inter-crossing between several species native to South Africa including P. zonale, P. inquinans, P. scandens, and P. frutetorum. Geraniums rank number one in terms of units sold among potted flowering plants and number three in terms of wholesale value. Sales increased through the 1970 and 1980's but have leveled-off over the past 10 year, possible due to the widespread availability of seed geraniums.

The traditional zonal geranium product has red flowers, green foliage, and is grown in a 4" pot. This product remains the bulk of the market. Customers are now seeking different container sizes, different flower and foliage colors, and cultivars that perform in sun or part shade. They also want cultivars suited to large open gardens, planter boxes, window sills, and hanging baskets. The two major suppliers of zonal geranium cutting material include Oglevee Ltd. and Fisher.

Crop Starting Options

Years ago, growers retained selected plants from the seasonal crops as stock plants for the subsequent season. These plants were maintained either in the greenhouse or planted outside for the summer and fall, then repotted and brought inside before the first frost. Cuttings were taken in winter, rooted, and maintained under minimum conditions until early spring for forcing. Several events precipitated a drastic change in this procedure. The economics of greenhouse space utilization combined with the development of "fast cropping" made the old procedures impractical. The development of serious systematic diseases almost always lead to the demise of the crop, mainly Xanthomonas campestris pv. pelargonii (bacterial wilt).

Today, vegetative material almost exclusively comes from specialized propagators that use culture-virus-indexing and other laboratory procedures to eliminate bacterial wilt and other systematic organisms such as vascular wilt, bacteria, virus, and fungi. The purchase of culture-indexed, clean materials is essential to successful zonal geranium production.

Two propagation options are widely used by geranium growers: 1) Purchase "clean" cuttings of named cultivars for growing stock plants, from which cutting are taken for production. 2) Purchase of rooted cuttings of named cultivars from specialists propagators directly for production. The decision to grow stock plants and carry out propagation in-house verses ordering rooted cuttings is largely an economic one, and depends on the size of the operation, the space and facilities available, and the skill of the growing team. Some propagators have recently provided a third option. Unrooted cutting can be ordered at a reduced cost compared to rooted cutting for those growers who have the facilities and wish to root cuttings in-house.


The success or failure of a stock plant and propagation program for geraniums depends on strict adherence and awareness on the part of employees for sanitation! Use the following rules:

1. Steam or chemically treat all pots, flats, media, etc. that may come in contact with plants.

2. Raised benches with surfaces that are easy to sanitize are preferable.

3. Disinfect benches, walks, sidewalls, etc. between crops.

4. Disinfect automatic irrigation systems and hoses between crops.

5. Use only culture-virus-indexed cuttings.

6. Break cuttings from stock plants, avoid using knives.

7. Isolate individual production steps from other crops.

8. Do not let hose ends or breakers touch the floor, hang them up.

9. Enter the stock plant area only with clean cloths and hands.

10. Employees should wear disposable gloves when handling stock or cuttings.

11. Never dip cuttings in solutions or powders.

12. Avoid moving or touching media or pots unnecessarily.

13. Avoid practices that might splash or move media from the floor to the bench tops or pots.

14. Don't put your feet on the bench!

15. Limit and supervise casual visitors.

16. Remove all weeds from within the greenhouse and within 30-feet outside the greenhouse.

17. Educate employees on the above and define for them "clean zones".

18. Train employees to recognize and remove any suspect plants.

Sanitation of equipment may be accomplished using Physan, Greenshield, or a 10% household bleach solution.

Stock Plants

Geranium stock plants are generally a long term crop so care should be taken in media selection and cultural practice. Rooted cutting for stock plants are generally potted into containers from 6" pots to bushel basket size containing a well-drained, well-aerated, peat-lite medium that does not compact and decomposes slowly. Dolomitic limestone to pH 6.0-6.5, superphosphate at a higher rate (up to 12 lbs/cu.yd.), and micronutrients in the fritted form are added to the medium. Watering is usually do using an automatic system, e.g. microtube watering. Full sun is usually supplied to stock except in the summer to reduce heat. Stock plants are usually fertilized using a tank mix rather than commercial fertilizer so that nutrient levels can be adjusted based on monthly soil tests. Start fertilizing at 250 ppm nitrogen and potassium.

Tissue analysis levels for geranium stock

Element Level
Nitrogen 3.3-4.8%
Phosphorus 0.4-0.67%
Potassium 2.5-4.5%
Calcium 0.8-1.2%
Magnesium 0.2-0.52%
Iron 70-268 ppm
Copper 7-16 ppm
Boron 30-280 ppm
Manganese 42-174 ppm
Zinc 8-40 ppm

Three methods of stock plant scaffold management are commonly used:

1. Tree-form stock production.

A large container is used with a 3-4 foot stake in the middle of the media. A rooted cutting is planted next to the stake in June, and the terminal is never pinched. Side shoots are soft-pinched at 6" long to develop secondary laterals. The central leader is tied to the stake, side shoots are pinched, and flower buds and large leaves are removed weekly. By December, a tall, bushy "tree form" develops and all terminals are pinched. Harvesting can begin in January and February.

2. Conventional stock production.

Using this method, cutting may be potted into large or small container from May to August depending on the number of cuttings desired over the life of the stock plant. Four weeks after potting, the cuttings are soft-pinched at 6" tall resulting in 3-5 lateral breaks. Cuttings are then taken every two weeks leaving 3-4 nodes for additional breaks. These early cuttings are often discarded. All flower buds and large leaves should be removed. In October, November, and December, a radical defoliation should be performed to allow light into the plants and reduce potential disease problems. Harvesting of cuttings can begin in January and February.

3. Multiplication stock production.

This method uses smaller containers, usually a 6" pot, and a shorter production time. Rooted cuttings are potted in November or December and cuttings are removed, rooted, and potted as they become available. Continue taking cuttings from all plants as early cuttings become stock plants. By early spring, a 1 to 40 (original cuttings to final cuttings) increase in plants can be obtained with this method This is the most efficient use of greenhouse space and requires no special skill developing stock plant scaffolds.

Ethephon (Florel, Pistil) sprays to stock plants will increase cutting number by 20-30% and act as a growth retardant reducing internode length, leaf size, and delay flower development. It should be applied at 350-500 ppm after pinching or after cuttings are removed. Ethephon application just before cutting removal may increase rooting. Gibberellic acid at 15-25 ppm can also be applied 3-4 weeks after potting cuttings to stretch internodes and build a taller scaffold.


Cuttings - Cuttings should be harvested early in the morning, preferably by snapping them off manually. Terminal cuttings should be about 2-inches long (larger is not better) with two maturing leaves. Remove any basal leaves that may end up below the soil line. In cases where cutting material may be limited, single-eye cuttings may be used. A stem may be divided into several single-eye cuttings composed of an internode and node with attached leaf and dormant lateral bud. Single-eye cuttings require 2-3 weeks longer to reach a flowering stage.

Medium - Geraniums may be rooted in a variety of media from conventional peat-lite media to specialized cubes, trays, or strips using peat, rockwool, or other synthetics. This may include cell-packs, Jiffy strips, Oasis blocks, or Jiffy pellets. Regardless, rooting medium must be exceptionally well-aerated, well-drained, and sterile with a pH or 5.8-6.2. Some sources recommend a rooting hormone while others do not. If used, 500 ppm Indolebutyric acid (IBA) works well. Cuttings should not be dipped into hormone solution or powder. Liquids may be sprayed on the cutting bases. Powders may be applied to the cutting bases using a "puff-duster". Dipping cutting in 2500-5000 ppm B-Nine the day before sticking can also speed rooting.

Spacing - Stick the cuttings into the rooting medium - to -inches deep but no deeper. Geranium cutting should be spaced so the leaves of adjacent cuttings do not overlap, about 2" between cuttings or 22 to 36 cuttings per square foot. Botrytis can be a serious problem in propagation and adequate spacing and excellent ventilation will help.

Temperature - The most rapid rooting occurs with a 60-62F night temperature in combination with 68-72F bottom heat. Try to keep day temperature 75-80F.

Light - Geranium cuttings need high light during propagation but can benefit from some shade late in the spring to control temperature. In propagation, light levels should be 1800 to 2800 foot-candles until roots form (12-18 days) then 2800 to 3600 foot-candles until transplant.

Carbon Dioxide - Supplemental CO2 at 800-1000 ppm increases rooting speed and early root system growth.

Stock-plant Factors - The environmental and nutritional condition of stock plants can have a big impact on the rooting of cuttings. Over-succulent cutting root poorly. Moderate moisture and temperature with high light is best for optimum cutting results. The highest rooting percentage is obtained when stock plants receive medium nitrogen and high phosphorus and potassium.

Scheduling - Roots should appear at the base of the cuttings in about 12 to 18 days from sticking. Cuttings are usually read to transplant in 3-4 weeks.

Mist - Mist intervals will vary with the condition of the cuttings, time of year, environmental conditions, and the performance of the misting equipment. The goal, however, is to maintain foliage turgidity with a minimum amount of foliage wetting. There should be little or no run-off into the propagation medium. As a beginning point, start with five seconds on every five minutes on the first day. Watch the foliage and adjust as needed. Decrease the mist interval until misting ends by day 18. Mist at night for the first six days at five seconds on every 30 minutes.

Fertilization - Do not fertilize the cuttings until roots are present. However, as soon as roots appear begin fertilizing with 250 to 300 ppm of nitrogen and potassium.

Finishing "Fast Cropping Geraniums"

This cultural procedure is used to produce a 4- to 4-inch pot geranium with one flower open in about 6 weeks from a rooted cutting (10 weeks from an unrooted cutting). Procedures are very exacting and requires exceptional attention to detail.

1. Pot 2" rooted cuttings 6 weeks before sale in peat-lite medium at pH 5.8-6.2. Unrooted cuttings may be direct stuck in the pots to finish in 10 weeks. Maintain the plants pot-to-pot for 3-4 weeks then space at 4 plants per square foot.

2. Irrigate as follows: Day 1 three irrigations 1 hour apart, day 2-4 one irrigation each day at mid-day, By day 7, white roots should be at the edge of the soil ball, if not leach!

3. Bottom heat is essential for this method. Night temperature should be 65F with a 70-72F media temperature. Do not vent or cool until the day temperature reaches 80F. The success of this method relies on new growth in the first week!

4. Provide 3500-4500 ft.ca. of light, some shade may be needed late in the season.

5. Use a constant liquid feed of 15-15-15 or 15-0-15 at 250 ppm nitrogen with no clear water after day 7 or use 350 ppm nitrogen every 3 out of 4 irrigations. Make sure that a 10% leach occurs at each fertigation. Use a monthly application of epsom salts at 16 oz. / 100 gal.

Zonal geranium normal foliar analysis ranges
N 3.3-4.8
P 0.4-0.7
K 2.5-4.5
Ca 1.0-2.0
Mg 0.2-0.7
B 30-100
Cu 7-16
Fe 100-300
Mn 40-150
Zn 10-50

Most zonal geranium products are marketed from early April into June. The most popular container sizes are 3" pots, 4-4" pots, and 6-6" pots. A few zonal geranium cultivars recently on the market perform well in hanging baskets.

6. Inject CO2 as long as possible at 1000-1500 ppm starting 1 hour before sunrise and continuing to mid-afternoon or 80F, whichever comes first.

7. Cycocel: 1500 ppm 14 days after planting and a second application 14 days later only if needed on vigorous cultivars. Or Cycocel at 750 ppm beginning 14 days after planting and 3 to 4 times at weekly intervals as needed. Apply only to well-fertilized, unstressed plants. Apply early in the morning or on cloudy days. Spray a light mist or to glisten, never to run-off.

8. At no time should the plants suffer moisture stress. Do not pinch the cuttings.


Whitefly, aphids, spider mites, fungus gnats, and caterpillars can all be problems on geraniums. In recent years, whitefly has been a persistent and difficult to control problem.


The list of diseases that can be a problem on geraniums is extensive:

Bacterial blight Blackleg Alternaria leaf spot

Bacterial fasciation Cutting rots Virus diseases (extensive list)

Cottony stem rot Black root rot Rusts

Bacterial leaf blight Verticillium wilt Southern blight