We are going to start our 2021 diary with a little experimentation. We haven’t grown watermelon for a number of years and have decided that we would like to try a couple of plants this year. After doing some research online we have decided we would like to learn to graft watermelon. Some of the benefits of watermelon grafting would be disease resistance and plant vigor. This will be totally new for us and we do not really know how it will turn out. We may have to grow traditionally if we can’t master the grafting process. Apparently, one of the most important things to have after grafting is to have some sort of healing chamber for the newly grafted plants to go into. This healing chamber needs to be kept at and a very high relative humidity at first and then slowly reduced over the course of a week. The grafts need to be in the dark for the first two days and then slowly introduced to light a little longer each day.
The picture below shows our newly built healing chamber (24” X 28” inside dimensions) with the control box on the right.
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The control box contains a SHT2000 temperature and humidity controller. It is wired in such a way so that one half of the outlet supplies power to the humidifier and the other half delivers power to the heater. It is very easy to make changes to the settings to either raise or lower the heat/ humidity inside the box. The red display is the temperature and the blue is the humidity.
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We started some seeds January 15 just for practice. We decide to use bushel gourd as the rootstock mainly because it was available to us. Unfortunately, we had very poor germination of the bushel gourds and we were only able to get 3 seedlings started from that batch. Today, we decided to try the first practice grafts. There are a number of different grafting techniques, but we decided for this first try to go with the one cotyledon graft.
This is one of the bushel gourd seedlings. They were not the healthiest looking plants but it’s all we had.
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Here is the same plant after the true leaves as well as one of the cotyledons were cut off on an angle down the stem.
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Next, is the watermelon scion that was cut on the same angle to hopefully match the cut on the bushel gourd.
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Next a grafting clip was put on the stem
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The seedlings were put inside the healing chamber and covered to keep light out. The humidifier is just a small bottle cap humidifier that fits inside a water bottle. The heater is a germination mat under the wire rack. The black probe on the top right is connected to the SHT 2000 controller. It measures both the temperature and the humidity.
It’s been a week since we grafted the watermelon on to the bushel gourd rootstock. The plants are looking a little rough, but they are still alive. We kept them in the dark for two days at 95% relative humidity. After that we introduced light into the healing chamber and we believe we might have injured the plants by using a light that was too intense. We also reduced the humidity inside the box a little each day.
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Here is a closer look at the plants. The watermelon cotyledons on this first plant have completely died off. It looks like the true leaves are still growing.
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The next plant shows the same die back of the watermelon cotyledons. This plant also has regrowth of the bushel gourd that shouldn’t be there. We need to make sure that the growing tip of the bushel gourd is completely removed next time. We will cut away the new growth of the BG as well as the dead cotyledons and continue to grow these plants to see how they do.
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This last plant seems like our best one. The cotyledons are a little yellow and you can see a little bit of BG regrowth just above the grafting clip that needs to be trimmed off. Overall we are happy with the results, so far. At least we are learning. We have started another batch of seeds and will try another set of practice grafts in a few weeks. We may attempt the hole insertion graft next.
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We have the healing chamber set up into a growing chamber right now with glass top and light. All the grafts are still growing well and we have some new plants just starting for more practice grafting.
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This is a look inside of the box with new plants in various stages. First grafts are in the back right
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All the grafts that we did a little over two weeks ago look good. This is a closer look at one of them.
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Today we completed our second batch of practice grafts. We have our seedlings pictured below. Six watermelon on the left and eight bushel gourd on the right. This time we are going to be trying the hole insertion technique. All the seedlings are a little more than two weeks old.
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First we remove all the true leaves of the bushel gourd.
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Two cotyledons are left.
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Next, a shaped wooden stick is carefully inserted at an angle down between the cots far enough that it comes out the side of the stem slightly.
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The watermelon is cut off from its roots. The stem is cut at a steep angle, rotated 90 ° and then cut again forming a sharp point.
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The watermelon scion is then inserted into the hole, with the cut edge down, far enough that the point should be showing a little out the side of the stem. The picture below shows that the point on this first one, is showing through too far. The hole was made too large. Not sure if this one will make it.
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This next picture shows one that worked out a little better. The point is just showing slightly.
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Below, is a look at all the finished grafts before they were placed into the healing chamber. We have the six on the left that are watermelon grafted to bushel gourd rootstock. The one on the right are the two bushel gourds we had left. We grafted them together just because we had extra plants. They all go in the dark for two days, in 95 % humidity. The watermelons may have been slightly too large for this method. Should have started them a week later maybe.
It has been 4 days since we completed the grafts. Below is a look at the plants. We had mixed results. We understand now why they say that the hole insertion technique is the hardest to master. Everything has to be perfect in order to get a good union.
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Here is a closer look at some of the poorer unions. This first picture is the one that we made the hole too large and the scion was inserted too far. Not sure how this one is still growing, but it is somehow.
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This next one sort of split out of the bushel gourd stem, but it is still growing as well.
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And finally this one totally rejected the scion.
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So we have 3 poor ones and 3 good ones. Below is an example of what we think is a good one. It looks like it has good contact with the BG and has a gel like substance covering the joint.
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This is an update on the watermelon test graphs. We only had two plants survive from the hole insertion grafts. It seems to take about two weeks before the plants recover from the shock. The plants below are 16 days old, since grafting day. They are finally starting to grow now. We will have to factor this extra stress time in when starting the actual watermelon for our patch.
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This is a close up of the graft union.
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Today, we ran the disk over the patch. It was ploughed last fall. It has been so nice here lately with no rain. We thought it would be a good chance to at least level out the patch a little. The ground is very dry.
This is very unusual for us this early in the season.
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