An Introduction to the Process of Grafting in Greenhouse Tomatoes- Part 1

An Introduction to the Process of Grafting in Greenhouse Tomatoes- Part 1 

By Dr. Natalie Bumgarner, Horticulturist

CropKing, Inc. Lodi OH

  A row of young grafted and ungrafted tomato plants

 being trialed in our research greenhouse in Lodi, OH.

 All the grafting was done on site this winter. 

Grafting sounds interesting, so where should I begin?In the last blog post, we discussed some of the basics of grafting and the main reasons that growers would be interested in the technique. It is no surprise that over the last few decades, the use of grafting has become quite prevalent in greenhouse tomato production. While the benefits are intriguing for small to mid-scale producers, decisions related to acquiring grafted seedlings must be made.The two broad options are to purchase grafted seedlings or to produce all the seedlings needed in your operation on your own. Seedling purchase and transport costs can be quite high in some instances. So, producing grafts for your own operation is a viable option. It also provides the opportunity to trial a limited number of grafted plants or test different cultivars.  There is certainly a learning curve for producing grafted plants, though. So, I would suggest starting by only planning to graft a small portion of  your crop the first year to become familiar with the process and it potential benefits in your operation.  

Overview of the grafting process

There are three crucial steps in the process of grafting your own tomato plants.  1) Setting the Stage, 2) Doing the Grafting, and 3) Healing the Grafts. 

1.Setting the Stage-

             It is important to remember that grafting will change the space and time needs of your typical seedling production schedule. It will also require some investigation into rootstocks that will best fit with the cultivars you are currently growing (now referred to as scions). Rootstocks, like greenhouse tomato scions, tend towards more vegetative or generative growth patterns, and these attributes will influence how they will perform in your greenhouse operation. It will likely be beneficial to try a few different rootstocks to determine how they impact your crop.

             Also, more seed will need to be ordered, and seeding will need to take place earlier to meet typical schedules. It is best to allow an extra week or two in your schedule to account for graft healing. Due to seeding both rootstocks and scions, more space will be needed in the seeding area as well. Prior to beginning seeding for grafting, it is also important to do some seed germination trials as rootstocks and scions may not have the same germination percentage or rate. Growth rate of the seedlings may also differ. Having rootstock and scion plants of similar size is critical for grafting,  so multiple seedings are recommended .  Remember to keep detailed records of seeding and germination as these will be valuable in planning for future years.

2. Doing the Grafting-

             There are several methods of grafting, and benefits and potential drawbacks to each. For further information on some the grafting technique variations, the resources listed at the end of this post provide additional discussions. In current greenhouse tomato propagation, the most widely used method is the tube graft (also known as the splice graft or Japanese top graft). The tube or splice graft is what I have used for grafting in the CropKing research greenhouse. The advantages of the tube graft are the young plant size at which it can be completed and the potential for high throughput in grafting operations. It is a method than can be done quickly by hand, but it is also suitable for mechanized grafting as is more often carried out in Europe.  

             Before grafting begins, make sure to adequately address sanitation in your operation. Sanitation is very important in the grafting process, and poor practices in this area have caused loss to both propagators and growers in the past. The process starts with using high quality, clean seed ( and therefore plant) materials. Then care should be taken during the process starting with clean work surfaces and utensils. Periodic changes in razor blades and hand washing are also important steps during grafting.  So, without further delay, let me give you a brief overview of the main steps and techniques used for tube grafting that would be appropriate to use in your own greenhouse tomato crop.

Where to find additional information

Many Land-Grant Universities are currently carrying out research and publishing information in the area of use and management of grafted tomatoes. While some of the research is tailored to soil-based, outdoor or high tunnel production, there is still much the soilless greenhouse grower can learn from these publications- especially on the topic of grafting and healing methods. Some grafting related materials from universities active in the area include: 

Ohio State University

North Carolina State University

University of Arizona

An Introduction to the Topic of Grafting in Greenhouse Tomatoes

An Introduction to the Topic of

Grafting in Greenhouse Tomatoes

By Dr. Natalie Bumgarner, Horticulturist

CropKing, Inc. Lodi OH

Grafting- What and Why?

Grafting has become very prevalent and important in greenhouse tomato production, and there are a couple of key reasons this is the case. Before we explore those reasons, let’s take one quick step back and discuss the basic premise of grafting. Many who are familiar with crop production are aware that most tree fruits are produced with a root system (rootstock) and above ground fruiting portion (scion) from different plants. This same principle is now carried out in many vegetative crops where two separate seedlings are produced and then joined together through the grafting process to produce one plant for transplanting. The use of grafting enables breeders to develop crop cultivars specifically for the demands of root and shoot environments and functions.

A tomato plant immediately after being grafted 

A young grafted plant for hydroponic greenhouse

production that has already been grafted and healed

Grafting can provide many advantages, but they mainly fall into the three main categories of disease resistance, stress resistance, and enhanced vigor and productivity. The use of grafting can reduce risks of disease (often affecting root systems) due to the incorporation of resistance traits in rootstocks not present in some popular scion cultivars. This is especially important in soil production. Grafting also is being used in many regions and systems to address heat, cold, salt and other forms of stress present in the growing medium or environment. The final key area of benefit is that rootstock cultivars can be more vigorous in their growth habit. This benefit is one of the most important for greenhouse producers because increased nutrient and water uptake can lead to enhanced fruit production if properly managed. However, it is important to remember that plant stress and disease resistance and vigor can sometimes be related. Increased rootstock vigor can enable the plant to better withstand stressful conditions and still maintain productivity.

A small batch of young grafted plants approximately one week after grafting. 

Who is Grafting and When may a Grower Choose Not to Graft?

Currently grafting of vegetable crops is carried out in many countries around the world for a variety of crops. The most commonly grafted plants are tomatoes and peppers (Solanaceous) and cucumbers and melons (Curcurbit). These are high value, longer season horticultural crops where the added investment in grafting tends to be the most economically advantageous. Getting a little closer to home, a large percentage of the large North American greenhouse growers are using grafted tomato plants to take advantage of the benefits discussed above. Currently, the use of grafted tomato plants tends to be less common in small to mid-size greenhouse operations for several reasons.

Plant availability is one of the main reasons that grafted plants are not used. Most large growers are acquiring their plants from specialized propagation houses, and the high shipping costs are overly burdensome for many smaller growers who need a few hundred plants rather than many thousand plants. Grafting can be done on site, and this is certainly an option for growers. In fact, we will discuss the main steps and practices of grafting in your own greenhouse in the next blog post. However, time and space needs for grafting on site are higher than for typical seedling production, so this option is not desirable for everybody. 

Whether ordered from a propagation facility or grafted on site, the cost of grafted plants can be higher than seedlings because we are seeding two plants. Exact cost differences depend of production and training practices such as whether one or two stems are trained from the grafted scion (more on this in the future). These potentially higher seed/plant costs linked with shipping costs can be prohibitive for smaller growers. Another reason for the use of seedlings rather than grafted plants is the ability for growers to produce all the plants they need in their own operation. By controlling the site and environment of production, growers can reduce some disease risks in their young crops.  The duration of production in a greenhouse tomato crop can also influence whether grafted plants are optimally beneficial. Some growers who have shorter seasons in their operation may not achieve the benefits required to offset the added investment in grafted plants.

So, it is clear that there are certainly benefits and some drawbacks in the use of grafted tomato plants in the greenhouse. We at CropKing are currently researching grafted tomatoes in our greenhouse and will continue to explore these questions and concepts in an effort to provide useful information and enable growers to make the best choice for their operation and crop. 

Cultivar Report 12.2- Varied Leaf Trial

Variety Trial Report- Fall/Winter 2012

CropKing Research Greenhouse- Lodi, OH

Cultivar Report 12.2- Varied Leaf Trial

Dr. Natalie Bumgarner

Objective

Hydroponic lettuce production in the United States now encompasses a wide spectrum of lettuce types and cultivars. While Bibb cultivars still occupy a large percentage of the market, many growers are also seeking attractive and distinctive lettuce cultivars to meet consumer demand. Due to these factors, leafy cultivars, including looseleaf and Lollo Rossa types, are becoming more common in hydroponic greenhouses. However, many of these cultivars have been more often grown in soil based systems, and there is a need to better understand their performance in the greenhouse. Consistency in both productivity and timing is important for greenhouse growers, and seasonal conditions can have a large impact on cultivar performance. Trialing of available cultivars under differing environmental conditions as influenced by seasons is important in informing grower decisions. Important points of evaluation are germination and seedling quality as well as growth rate, yield and visual coloration. The goal of this set of trials was to evaluate a selection of leafy lettuce cultivars through a range of late fall, winter, and early spring conditions to evaluate their potential for greenhouse growers in the Midwest and northeast. Cultivars were obtained from a variety of seed suppliers to represent a broad selection of cultivars available to lettuce producers.

Materials and Methods

Plant Management-

All plants were grown for the entirety of the crop in the CropKing research greenhouse in Lodi, OH. Primed and pelleted seeds were seeded by hand in pre-moistened (with pH adjusted water) 1” x 1” x 1 ½” rockwool cubes. Seeds were germinated uncovered in clear water in seeding trays in the CropKing nursery area. Nutrient solution was added in the nursery 7 days after seeding. Seedlings were produced in flowing nutrient solution as described below for an additional two weeks prior to transplanting. For the final week before transplanting to the channels, plants were grown in the nursery under supplemental lighting (6 bulb, 4 ft., T5 fluorescent light) on 16-hr days. After transplanting, lettuce plants were grown out in the channel for five weeks prior to harvest. Fourteen plants of each cultivar were produced. Total production time was approximately eight weeks reflecting low light conditions typical of many Ohio winter production schedules.

Figure 1. Seedlings at transplant (3 weeks after seeding)

Growing System-

After transplanting, lettuce was produced to harvest in CropKing NFT channels. These 4” wide growing channels are food-grade, UV resistant PVC with matching top caps punched to fit rockwool or other similar growing mediums. Spacing for plant production is 8” within and across channels. All channels are fed by nutrient feed lines supplied a continually recirculating nutrient solution. Each channel drains into a completely closed drain line which returns the nutrient solution to the reservoir. Galvanized steel frames support the channels and the drain line. Solution is also continually cycled through the CropKing Fertroller where automatic pH and EC adjustment is carried out to meet programmed solution set points. The pH was maintained at 5.8 by the addition of dilute sulfuric acid. EC was maintained at 1.8 by the addition of concentrated fertilizer solution and source water.

Greenhouse Conditions-

	Air temp. average (°F)	Relative Humidity average (%)	Solar radiation average (W/m2)*	Carbon dioxide (ppm)
10/24 to 12/19 trial	66.4	70.5	57.2	449.5

*Solar radiation reflects ambient greenhouse conditions and does not include any supplemental light applied during the seedling stage.

Nutrient Solution Formulation-

Nutrient solution was supplied by the Fertroller system discussed above. Stock solutions #1 and #2 were prepared using greenhouse grade calcium nitrate, potassium nitrate, magnesium sulfate, monopotassium phosphate, DTPA iron chelate, and CropKing MicroMix. Nutrient solution formulation was based on laboratory results from on-site samples of source was and were intended to reach macro and micronutrient targets specific for leafy crops in NFT systems.

Results

Cultivar	Germination % (Fully emerged and viable seedlings 6 days after seeding)	Cultivar Individual Head Wt. (g ± SD) n=14
Carmesi	100	41.2±9.0
Livigna	96	56.7±11.0
Locarno	100	52.1±13.7
Lozano	100	63.1±9.9
Nevada	88	60.7±13.3
New Red Fire	96	77.4±15.8
Orville	100	50.7±12.3
Ruby Sky	88	84.3±23.3
Teide	92	55.2±12.0
Tropicana	100	159.5±26.1

Figure 2. Mature lettuce plants immediately prior to harvest.

Discussion

This initial evaluation of leaf lettuce cultivars demonstrated growth rate differences as well as potential variation in suitability for winter production in northern areas. For most cultivars, germination was similar and seedlings were all of appropriate size at transplant (Figure 1). However, by harvest, differences in size and plant form were apparent (Figure 2). Light levels in this production season were greatly reduced from summer and early fall conditions. This reduction in light potentially impacted this lettuce crop in three important ways. First, reduced solar radiation slowed down the growth of the crop and lengthened the production time from approximately 6 total weeks in the summer to 8 weeks in this winter study. Secondly, plant appearance was impacted as these low light levels contributed to plant stretching or undesirable stem elongation (some stretching is even apparent in Figure 1 at the seedling stage). Cultivars, such as Locarno, Tropicana, Ruby Sky, and New Red Fire, all exhibited some degree of stretching in some or all of the lettuce heads. Additionally, reduced leaf coloration in both red and green cultivars also may have been a result of lower solar radiation in this study. These results indicate that in some climates, certain cultivars may require supplemental lighting to be most marketable for year-round production.   

Time Lapse of Lettuce growing in CropKing's NFT Channel

We are still running variety trials in the greenhouse.  Here is a time-lapse from one of those trials.

Cultivar Report 12.1- Butterhead Trial

Variety Trial Report- Summer/Fall 2012 

CropKing Research Greenhouse- Lodi, OH Cultivar Report 12.1

Cultivar Report 12.1- Butterhead Trial Report

Dr. Natalie Bumgarner

Objective

Hydroponic lettuce production in the United States now encompasses a wide spectrum of lettuce types and cultivars. Producers desire both attractive and distinctive crop cultivars to meet consumer demand, but consistency in both productivity and timing is still a key in the industry. Many facets of hydroponic lettuce production are impacted by seasonal conditions. One of the most important environmental impact of season is the growth rate of the plant. Growth rate is the driver of productivity and determines crop timing and the number of crops a grower can produce each year. Additionally, crop quality aspects, such as coloration and physiological defects (tipburn) are often influenced by seasonal conditions. Therefore, trialing of available varieties under differing environmental conditions as influenced by seasons are important in informing grower decisions. The goal of this set of trials was to evaluate a selection of bibb lettuce cultivars through a range of late summer to mid-winter conditions to evaluate their potential for growers producing fall to winter. Cultivars were obtained from a variety of seed suppliers to represent a broad selection of bibb cultivars available to US lettuce producers.

Materials and Methods

Plant Management-

All plants were grown for the entirety of the crop in the CropKing research greenhouse in Lodi, OH. Primed and pelleted seeds were seeded by hand in pre-moistened (with pH adjusted water) 1” x 1” x 1 ½” rockwool cubes. Seeds were germinated uncovered in clear water in seeding trays in the CropKing nursery area. Nutrient solution was added in the nursery 7 days after seeding. Seedlings were produced in flowing nutrient solution as described below for an additional week prior to transplanting. Transplanting occurred two weeks after seeding. After transplanting, lettuce plants were grown out in the channel for four weeks prior to harvest. Total production time was six weeks.

Growing System-

After transplanting, lettuce was produced to harvest in CropKing NFT channels. These 4” wide growing channels are food-grade, UV resistant PVC with matching top caps punched to fit rockwool or other similar growing mediums. Spacing for plant production is 8” within and across channels. All channels are fed by nutrient feed lines supplied a continually recirculating nutrient solution. Each channel drains into a completely closed drain line which returns the nutrient solution to the reservoir. Galvanized steel frames support the channels and the drain line. Solution is also continually cycled through the CropKing Fertroller where automatic pH and EC adjustment is carried out to meet programmed solution setpoints. The pH was maintained at 5.8 by the addition of dilute sulfuric acid. EC was maintained at 1.8 by the addition of concentrated fertilizer solution and source water.

Greenhouse Conditions-

	Air temp. average (°F)	Relative Humidity average (%)	Solar radiation average (W/m2)*	Carbon dioxide (ppm)
8/8 to 9/20 trial	70.1	81.9	141.9	461.4
9/12 to 10/23 trial	68.6	70.7	131.2	445.4

*40% white shade cloth was in place from 8/8 through 9/14 when it was removed. Thus solar radiation averages reflect reductions in light transmission provided by the shade cloth.

Nutrient Solution Formulation-

Nutrient solution was supplied by the Fertroller system discussed above. Stock solutions #1 and #2 were prepared using greenhouse grade calcium nitrate, potassium nitrate, magnesium sulfate, monopotassium phosphate, DTPA iron chelate, and CropKing MicroMix. Nutrient solution formulation was based on laboratory results from on-site samples of source was and were intended to reach macro and micronutrient targets specific for leafy crops in NFT systems.

Results

Cultivar Individual Head Wt. (g) Seeded 8/8 Harvested 9/20 Seeded 9/12 Harvested 10/23 Adriana 181±20 119±20 Alexandria 129±25 103±14 Australe 109±18 93±13 Flandria 118±17 101±8 Gardia 137±36 122±21 Hungarina 158±35 124±30 Nancy 141±20 109±15 Natalia 109±21 94±16 Red Cross 144±23 82±11 Rex 116±13 81±10 Santoro 153±18 104±13 Skyphos 74±23 58±10 Teodore 89±16 53±10

Discussion

These two lettuce crops were produced on the same production cycle with consistent days to transplant and harvest. The yield data illustrate potential seasonal effects of decreasing light as the light intensity and day length tend to decline during fall in this northern latitude. Temperature differences, even of a few degrees, in these two runs of the trial could also have influenced final harvest yields. Additionally, it should be noted that reduced biomass was more pronounced in some cultivars than other indicating that some cultivars may be suitable for year-round production while others have seasons when production is optimized.