The Art of Topworking
Last week, I introduced the concept of grafting, that is, taking a part of one tree and sewing it to another. In terms of apples, this means producing fruit that is true to the parent tree and unlike planting an apple from seed, is predictable.
How to Topwork an Apple Tree
Many stonefruit trees can be grafted quite easily but today, I will discuss apples in particular. The general method will be similar for other fruits but the timing may be different depending on the tree’s yearly schedule.
Topworking is a grafting process in which you gradually change a tree from one variety to another. For simplicity, I will just list the steps. Continue reading for a few very important points that, if ignored, can result in a failed grafting experience.
1. Choose a base tree onto which you will be grafting your future scions. This tree should be well-established, ideally disease and insect resistant, and not on its way out. Remember that the new branches that grow from this tree (the ones you grafted), will have characteristics determined by the roots (or the base tree). This tree will have to be compatible with your desired scion varieties (apple and crabapple trees are best for apple scions but there are other options, too).
2. Select the apple varieties you would like to produce and source them. Take cutting from these trees (with permission, of course), while the trees are dormant but not frozen: ideally, early spring. Your cuttings should be the previous year’s vigorous growth and at least a foot long. Water sprouts generally make good, straight cuttings. Cut at a 45 degree downward angle below a bud. Use sharp tools to avoid damaging the donor tree and your scions. Place your scions in water immediately. How many you take will depend on how many grafts you have space for (6-10 per tree is plenty). Choose a number then add a few for those “just in case” moments.
3. Bundle and store your new cuttings. Store them in a moist 4-8°C. The easiest way to do this is to wrap them in damp paper towel, seal them in bags, and place them in the refrigerator. Keep an eye on them and watch for moulds. Do not store your scions where you are storing apples or pears as they produce ethylene and could potentially ruin your cuttings. Of course, don’t forget to label your cuttings – especially important if you are taking multiple varieties.
4. Choose your method. This is where it gets tricky. There are a number of different methods that will all lead to the same end result but one method may be better suited to your needs.
a. Cleft Grafting: used for rootstocks 1-4 inches in diameter when stock and scion are different diameters.
b. Bark Grafting: used for rootstocks 4-12 inches in diameter when stock and scion are different diameters.
c. Whip and Tongue Grafting: used when scion and rootstock are of same diameter (no more than 1 inch in diameter).
5. Prepare your root stock or base tree. This will depend on which method above you choose to follow. For cleft and bark grafting, a 90 degree cut perpendicular to the tree’s growth will work best. For whip and tongue grafts, you will cut at a 45 degree angle. Choose branches that are no more than 2 inches in diameter.
However you prepare the rootstock, remember that you are looking to expose the cambium. The cambium, the actively growing cells between the old wood and the bark, from the rootstock and the scion must touch in order for the tree to “repair” itself and create a solid connection between the two pieces. This connection will allow the scion to pull nutrients from the rootstock and grow as if it were always part of that tree. The larger the cambium connection, the greater your chances of grafting success.
6. Attach your scions. Using one of the above methods (which I won’t detail but you can read about and view images here), create the union (where the scion and rootstock are attached). Depending on the method you choose, your scions may need to be held in place with tape or string. Some grafts call for grafting wax or compound. Be careful to read the instructions for whichever product you choose. If you apply too liberally, the stock branch won’t be able to breathe and rot may set in.
7. Monitor your new grafts. Watch for rot, squirrel or other rodent damage, scion movement, and, of course, growth. Monitor the buds for growth and healthy ‘normal’ development.
8. Time to prune. Pruning your new grafts will not happen in the first year and may not even happen in the second year. Use your best judgement as each tree will grow at a different rate depending on how well the scions took to the rootstock.
If your ultimate goal is to convert an old crummy crabapple to a multi-variety apple tree, it will likely take a few years, especially if the tree is old with many crabapple branches. Remember not to remove all of the branches from a large tree in one go – more often than not, you will encourage suckering or simply damage the tree.
Grafting is a fun and easy way to produce the desired varieties using an existing tree you already have growing. After a few tries, you’ll have found the method that works best for you and by all means, I encourage you to research your particular situation. As you have seen, grafting comes in many forms.
Next week: budding! Another form of grafting.