Is Topworking Right For You?

Terry Bacon and David H. Byrne, Dept. Of Horticultural Sciences, Texas A&M University, College Station, TX 77843-2133

Introduction

Variety choice is crucial to orchard success. If you have ever planted a ‘dud’ variety you know this all too well. Perhaps the fruit was too small, or too soft to make it profitable, or it may have been a good variety but poorly adapted to your area, so that most years the trees do not bear and cost you more to keep alive than they produce. You may also have received ‘off-trees’ (rootstocks or other varieties) mixed in with your tree order. In most cases people will live with the problem for a few years and eventually push the unproductive trees out and start over. In the case of old or diseased trees this is the only option, but if you have healthy trees that are not more than six years old, you may want to try topworking.

‘Topworking’ refers to the grafting of a new variety usually onto a mature tree. In California where competition for ‘newer and better’ varieties (especially with white-fleshed peaches and nectarines) is very hot and trees live long healthy lives, topworking is a way of life. In the southeastern United States topworking fruit trees is not common. Trees in the southeast generally do not live as long, and disease and pest pressure is much greater than in California. There are however several reasons why topworking, at least on a limited scale, might be worth considering in this area. Possible reasons for considering topworking include:

1. Changing individual ‘off-trees’ that may have been included with your tree order so that they match the rest of the variety block. At best these off-trees are a nuisance to the grower because bloom and/or harvest is out of synch with the rest of the block. At worst, they can be a starting point for disease and pest infestation that can then spread throughout the block.

2. Changing an entire block of trees to get rid of an unproductive variety or to introduce a better one. You must be sure that the new variety has been tested in your area so that you are not replacing one dud with another. Changing over a block of trees can also be a way of redistributing the variety ‘make-up’ of the orchard by simultaneously reducing the number of trees of one variety while increasing the number of another.

3. Creating a variety test area in an orchard. Variety testing is important in this day when so many new varieties are being developed and topworking can be a quick, efficient way to develop an area to do this. The test area should be established at the edge of an orchard so that it will not interfere with orchard operations, but do not place it too far out of sight or it will be neglected and worthless.

Even if there is a reason to consider topworking, you must first weigh the advantages and disadvantages in order to decide whether it will be right for you and your operation.

Advantages of Topworking -vs.- replanting an orchard:

1. Topworking can make an orchard more efficient by replacing unproductive or poor quality varieties with better ones.

2. Grafted trees grow and become productive faster than newly planted trees because grafted trees have the force of an established mature root system behind them while newly planted trees do not. Furthermore, you are eliminating the time it takes to push out old trees, rest the land, and re-establish new trees.

3. Weed management and irrigation programs are already in-place in a mature orchard while they must be re-established in a newly planted orchard. Also, if good orchard land is scarce, the grower can better utilize a good site, with minimal disruption, while changing to a more productive variety.

4. Grafting is a simple operation that is easy to learn and to teach to others.

Disadvantages of topworking:

1. While grafting is simple and easy to learn, there are several steps involved and each must be performed correctly and timely or success will be greatly reduced. You must have a good understanding of all of the steps involved in topworking before doing it on a large scale.

2. You will be losing two years of production on existing trees as compared to just leaving them alone. The stock trees being topped should be relatively young (less than six years) and unproductive to make it worth the effort.

3. Heavy winds during May and June can blow out grafts. Because of vigorous growth, grafts are vulnerable until the graft union has fully healed. For this reason it is recommended to stake and trim the new growth.

4. ‘Newer-better’ variety could be a dud. It is important not to plant or topwork large numbers of a new variety unless it has been tested in your area for several years.

Cleft Grafting

Topworking is not a difficult procedure but there are a few critical steps and each must be done correctly and timely in order to have success. This article is intended to give a sense of the procedure of topworking in general, and the cleft graft specifically, but the reader should do further research to become fully prepared before doing it on a large scale. Book stores and libraries carry many very good books on propagation and grafting. It is also a good idea to try your hand on a few trees one year to become familiar with the technique before trying it on a large scale.

All types of grafting use a grafting knife that is sharpened only on one side of the blade. With the cleft graft, a special cleft grafting tool is used (pictured below) for splitting the stocks. It is also necessary to have grafting wax and/or non-phytotoxic ‘Tree-kote’ type wound dressing. All these items can be purchased through horticultural suppliers such as Hummert (800) 325-3055, A.M. Leonard (800) 543-8955, and in Texas; Womack’s Nursery (817) 893-6497.

Grafting is performed in early spring, but the process begins in January when you collect graft wood (scions) to be stored. To know how much to collect, look at the trees to be topped. Count on placing two grafts per scaffold limb and leaving one well-pruned ‘nurse’ limb. The nurse limb is one of the main scaffold limbs that will be left temporarily to reduce the shock to the root system that occurs when you remove most of the top portion of the tree. If you have typical open-center trained trees with three scaffolds for example, you will be grafting two scaffolds with two sticks each and leaving the third scaffold as a temporary nurse limb to be removed when the new growth is established. The scion wood you collect must be healthy fruiting wood that is 3/8”-1/2” thick and about 5” long. Do not use water sprouts or weak, thin wood for scion wood. The wood will be stored in ziplock bags in a refrigerator (about 350 F) until it is time to topwork. Do NOT store wet wood or place wet towels in the bags because this causes storage rot.

Grafting is done when buds on the stocks are beginning to swell but before growth starts. Remove the scaffolds to be grafted and discard them a few days in advance. The limbs for topworking should have 6”-12” of smooth, straight wood that is free of knots and be no more thatn 4” in diameter.

Grafting Procedure

For enhanced success, grafting should be done on a cool, overcast day with little or no wind.

1. Split the stock with the cleft grafting tool. If the sawed cut on the stock is rough you will need to remove about one inch of the limb with a hand saw to give a smooth surface to work with.

2. Prepare the scion wood by first pruning off the bottom 1/2” to get to fresh wood. Next, you will make long tapering cuts on both sides of the bottom of the stick to leave a ‘V’-shaped appearance that will fit tightly into the split on the stock. Note in the figure that the V-cut should be slightly narrower on the side of the scion that will face the interior of the stock.

3. Pry open the split on the stock carefully and place the scions. It is crucial to success that the cambiums of the stock and the scion are lined up and touching (see figure). The ‘cambium’ is a thin ring of living tissue between the bark and the interior wood on both the stock and the scions.

4. Seal the top of the scions and the stock with grafting wax or ‘Tree-Kote’ once the scions are in place. You must be careful to get a good seal or the graft union will dry out and the graft will fail.

After Care

After 2-3 days you should inspect each graft and re-seal any openings that might have developed. Many people like to white-wash the trunks to prevent sunburn. A 1:1 interior latex wall paint: water mixture is good for this. Periodically during the spring and summer remove re-growth from the stocks and trim excess side shoots off the scion growth (to prevent wind blow-outs). If growth is very vigorous, it is recommended to stake the new growth until the graft union becomes strong. This can be done by either fastening wooden stakes to the scaffolds, or by placing a stake (wooden or bamboo) in the soil, and tying new growth to it. Growth during the first season can be very vigorous and you should begin training to develop a well balanced open-center form. After the scions have grown sufficiently to support the root system, you should remove and discard the nurse limbs to reduce competition with the new growth.

Remember that, as with a newly planted block, frequent attention will yield the best success and bring the trees most rapidly into production. As they say, “Keep your shadow on the tree!”