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A healing chamber is necessary to protect the newly grafted plants while they are healing. For one or two plants, simply have a large plastic bag handy to place over each plant after the grafting occurs. For a larger number of plants, and a better chance of survival, build or purchase a large wooden or PVC frame, then draping it fully with polyethylene sheeting. Have a tarp or opaque shade cloth ready to block most sunlight from entering the chamber during the first stage of healing. Place a bench in the chamber to hold your plants. Use a frame with a peaked roof so condensation runs down the sides and doesn't drip onto the plants. Place shallow pans of water around the floor of the chamber to increase the humidity. Before you graft any plants, you should monitor the environment in the healing chamber for at least several days to make sure it is stable. The temperature levels should be constant between 70 and 80F (2127C) and the humidity should be 8095%. Note that you should not store any plants in this chamber until they are grafted. Grafting is most successful on young tomato and eggplant plants, whose stems are still green (herbaceous) instead of woody. The stems should not have grown noticeably thicker, and each plant is usually ready when it has 24 true leaves. The most important note to remember is that the two plants should have stems with exactly the same size, so they can grow together without difficulty. Note that the first one or two leaves the plant grows will be "seed leaves", not true leaves. These should be easily identified as they will be a different shape or size than the true leaves, but the exact appearance depends on species. If it's not possible to find stems of exactly the same size, you must use a rootstock (base) stem larger than the scion (top) stem. The other way around will not work. Use a sterilized razor blade or sharp knife to cut through the rootstock (base plant) and scion (top plant) stems. While the exact angle is not important, you should use the same angle for each so they fit together as closely as possible. Make the cut in one motion to keep the surface as flat as possible. Discard the top half of the rootstock and the bottom half of the scion plant. Cut each plant above the smaller lower "seed leaf" but below the higher, full size leaves to prevent the scion plant from attempting to grow roots, which can lead to infection. See Understanding Grafting Basics for more information on rootstock and scion plants. These clips may be made from silicone or rubber and should be available at gardening stores or online. Try to match the angles of the cut surfaces as precisely as possible, then hold the plants in place by closing the grafting clip around them. The plant must have time to grow the two vascular systems together, which allows sap to flow through the plant. During this time, keep the plant in a humid, dark environment to minimize the amount of water loss from the scion plant until this happens. The healing chamber described earlier is perfect for this, with an opaque shade protecting it from the sun. For a smaller operation, put a plastic bag over the plant and keep out of direct sunlight. Water the base of the plant or mist its leaves if the environment is below 85% humidity. You should keep the plant in the special environment for at least 4 days, and it will often take a week before the leaves return to a full, healthy state. Even then, you should gradually alter the environment for another few days, or up to a week. Increase the amount of sunlight it receives gradually and reduce the humidity by occasionally removing a pan of water or lifting up the plastic a little higher. Wilting is normal for the first day, but mist the plant's leaves if it occurs. If the plant continues to wilt for three or four days, the graft was unsuccessful. Although this method is quite reliable, this still happens about 5% of the time even in the best of circumstances. If the plant's leaves are still wilted, they are not likely to survive, or at least not likely to do well this growing season. The healthy plants can now be returned to normal growing conditions for a seedling about to be planted. The exact conditions will vary according to species. The point where the two plants are joined should be at least 1 inch (2.5cm) above the soil, to reduce the chance of the upper scion plant trying to grow roots. There is no need to remove the grafting clip, which should fall off on its own as the plant grows. Do not hesitate to prune away roots growing from the scion or shoots growing from the rootstock. You may also wish to prune away smaller branches so more energy goes into fruit production.
Construct a healing chamber in advance. Add pans of water to the chamber and monitor the environment. Choose plants that are 25 inches (513cm) tall and have equal diameters. Cut each plant in half at a 45 angle. Join the two plants together with a grafting clip. Move the new hybrid plant to a humid, dark environment immediately. Gradually return the plant to more sunlight. After two weeks, return surviving plants to normal growing conditions. Plant the hybrid with the graft clip well above the soil.