Grafting Solanum Cultivars

I'm on a never ending quest to grow tomatoes well in Dunedin. It would be a simple matter if there was a green house on the property I am renting, but I have not had such luck in the four years I have been here. There are many ways to get tomatoes off to an early start in most peoples cases. However, keeping Solanum alive over winter, cloning them and saving their sometimes unpredictable seeds can be a load of work! I Cant even get a good crop of eggplants or capsicum in our short season and my cape gooseberries need to be overwintered inside! I'm looking towards grafting to reduce my tomato workload and attempt another means to grow eggplant and capsicum. I though that many other Solanum enthusiasts in Dunedin might be trying the same.

My latest experiment is grafting Solanum cultivars. Though I intended to graft eggplants, the seedlings are not big enough yet. With my impatience, I started grafting standard (sized) tomatoes. I find that for myself grafting cherry tomatoes and small hot peppers to be a bit of overkill but if your eat a ton, make preserves or your plants do not like the soil or climate you have to offer it, you may want to give grafting a go. Grafting is a very basic skill and a bit of practice will get you on your way. Grafting entails splicing two different plants together to gain the advantages that both varieties offer.

Why Graft Solanum Cultivars:

Basically, most tomatoes are tropical plants. Some are bred to tolerate mildly wet or cold climates but the variation within the cultivars is very limited. Especially in the case of heirlooms, standard (sized) tomatoes, eggplant and capsicum. They tend to mature slowly and only a few fruits from each plant mature in time and are tasty. While the desired fruit may not do well in your location, a native Solanum from your area may help it grow better or faster or even perennially! A person may choose to graft plants for a few reasons.

1. You may find that certain Solanum do not like the soil or weather conditions and get a bit sulky. Plants which struggle will be more susceptible to diseases early and late in the season. You can graft a tasty variety onto the rootstock of a plant which can tolerate your climate and soil type.
2. To avoid root disease that can build up in pots or garden beds.
3. To extend the growing season (my main drive). What usually causes Solanum to die in winter is cold temperatures. By grafting, you are avoiding root sensitivity early and late in the season so that plants will start earlier, grow faster and hopefully produce better fruits. If I can find a suitable outdoor micro climate you could … Theoretically... (Depending on a lot of variables) be able to grow my tomatoes etc. outdoors perennially with a seasonal trim of the grafts and rootstock.
4. If you can avoid the above issues (via a greenhouse or micro climate) you may still increase your yield by grafting onto rootstock that is more vigorous even if your tomatoes are doing well enough.
5. Its Fun! And is potentially space saving. Who loves gardening and does not enjoy some botanical tinkering?

Weblog: Deep Green Permaculture; Grafting Eggplant onto Devil Plant

What types of rootstock to choose:

There are a few kinds of rootstock you can choose from depending on what the issues your tomatoes have with the soil/climate. You have two real options. One is to select hardy rootstock of the same species or to use a wild rootstock like Solanum Aviculare/laciniatum or poroporo/pöporo.

Say you have a nice cozy green house and grow plants as seedlings or clones every year. You can benefit from grafting more vigorous root stock and increase your yield (space saving). On the flip side you will also have to increase your pruning. If you grow tomatoes in the earth in your greenhouse (vs. potted) you may find soil pests can become a problem. Your greenhouse may be too small to rotate crops in, which I imagine would be the case for most people. A solution may be to use disease resistant tomato root stock. Alternatively you could graft onto a wild/native perennial Solanum and get both of the benefits along with the benefits of a healthier soil community from practicing a no dig plant culture. Say you have a warm, sheltered and sunny site. Maybe your site is a bit small and you have to replant in the same space every year. The same benefits as for a green house apply.

Say you have neither a green house, an ideal micro climate and no good windowsill to stick clones in over the winter. What do you do then? Say you would prefer to use your green house space or cozy micro climate for another, more practical plant?

Well, that is the situation I'm in. My windowsill is best utilized for starting seedlings, my garden is on a windy slope and the soil is boggy. My issue is that I only get one or two ripe standard tomatoes by the end of the season, because the cold ruins their texture and flavor in late fall. I can't even get close to harvesting an eggplant. The root stock I chose is poroporo. It was growing on the garden already and is well suited to the climate. It is a native, always a bonus. The fruit may be edible when overripe, has an arguably palatable taste, is toxic when unripe, and it is tricky to tell when it is safe to eat. I have heard of people who eat it but have not tried the fruits myself. I was inspired to use wild Solanum rootstock by reading about Australians using wild tobacco/devils plant to solve some of the same issues I was facing. Who were in turn influenced, I imagine, by the older European method of grafting onto a wild Solanum very similar to devils plant (a big thorny perennial Solanum).

There are many potential benefits of this method vs. using cultivar rootstock. One benefit is that the plants are perennial in this climate and do not need to be replaced yearly or transplanted (less work). Whether the perennial nature will translate over to the grafts is yet to be seen, but if I get the culture right it might be a matter of proper placement and trimming to keep the grafts alive over winter. I expect an earlier start, a more productive season and maybe, just maybe, a later harvest. Another possible benefit is better nutrition from the larger root system, with a potential to decrease fruit splitting. The deeper roots have access to deeper, wetter soils. This may mitigate the hot/sunny and overcast/raining days we see in a typical week of summer here.

Wild Root Stocks:
Tropical, Sub Tropical : Devils Fig
Temperate: poroporo/pöporo
List of Tobacco Species 

Graft techniques and what might work best for your situation:

All information about grafting comes from source [3]  

There are a bunch of different methods of grafting and variations within them. There are two main types of grafts you could use. One method is a complete severing of the scion from its original roots and the other is a partial severing. A completely severed scion heals faster and is generally best practice. If you are grafting onto rootstock outdoors, are not confident yet, or do not have steady hands, you can partially sever the scion from its original roots and allow it to remain attached to its own roots for a short time while it heals.

The other method begins with decapitating two plants. One with the roots you desire and one with the fruit you desire. You then fit their stems together and wait for them to heal. With all grafts its important that they fit together well by being the same stem diameter and that the outside cambiums touch for at least most of the graft. The better the fit the better the graft. Sanitation is essential for tools as is selecting rootstock and scions from plants that show no sign of pests or diseases. You must keep the plants from drying out by keeping the scion in water and working quickly.

Tools you need can vary from the sloppy cowboy approach which works well but is less successful, to the sophisticated hundred dollar tools that make perfect cuts that fit together like a jigsaw puzzle. Basically you need a sharp blade or grafting tool, a glass of water with or without something added to promote healing or prevent infection. Something to wrap around the graft to keep it moist, stop it from shifting and to prevent infections from getting in. This can be a tube, grafting clay, a clothes pin, a grafting clip or a stake and some grafting tape or strips of a plastic supermarket bag. Obviously, the more sophisticated the tools you use the better the graft will be, but a little practice can produce good results even if your using whats lying around the house. It took me two (cowboy) attempts to get successful grafts to stick.

Frankenplant Culture:

This is the really fun bit, and my favorite bit of the process. Plant culture is where gardeners shine, show off and compete amongst themselves. Whether its super scientific compost building, elaborate training, or in my Pop-pop's case singing, there is a good amount of latent productivity you can coax from a plant. There are so many schools of though and even books on how to best grow a tomato that I wouldn't fit it into one blog post (especially since this one is so long already).

Growing a tomato grafted onto another tomato is essentially the same culture as an ungrafted one except you have to be careful that no roots sprout from the scion and that no laterals form off of the rootstock (unless your cloning more rootstock). You may graft the wild Solanum at the central stem and train like a normal tomato. Try to push it and see how many laterals it can support. The picture above is my Solanum grafts a few days afterward and that is my pet rat enjoying his small jungle.

The plants are bushes and have huge root systems compared to tomato's and they grow laterals constantly in sets of three. The bush itself splits its branches in threes and is beautiful and well balanced [1]. A gardener may graft many branches or graft onto the main stem of the plant. This may provide the solution to my miserable failures with eggplants. I see a lot of potential for growing hot peppers as well. Different kinds of tomatoes or cultivated Solanums can be grafted onto different branches of the same bush. However, different varieties of tomatoes and Solanums may have different growth rates and throw off the balance of the bush. For example a tomato might grow longer than an eggplant so the bush might become unbalanced. The quality of the graft may also create a difference in growth even if the scions are clones. Good supports or trimming should take care of this and keep your bush in the ground.

If espaliering this plant (for horizontal growth of tomatoes), it could make a beautiful and quirky plant. In the case of eggplants and some bushy peppers you may be safe to just let grow with a trim if things get out of hand. For tomatoes you would want some kind of support because these will still grow like a normal tomato does and flop over, stressing the graft union. As the plant produces laterals in threes you may be able to combine both cultures and grow two vine Solanums against a wall support and one bushy Solanum sticking out the front (like eggplant or some peppers). If grown against a warm surface like a brick or rock wall, then the residual heat may be enough to save the grafts from frost damage. Even though the grafts would most likely stop growing in the winter anyway [1], they may live to start early in the spring.

The root stock's own fruits are allegedly edible when ripe but are toxic when unripe and its difficult to tell when they're safe. I have heard of people eating the fruit but most of the information on this topic I found was from the experience of other gardeners. I read about online so if you plan on eating this plant's fruit, do a bit of research first.

How Grafting Fits into Permaculture methods:

If you can grow your desired Solanum as a perennial then you are able to add it to your garden. Personally, I find growing tomatoes more of a fun project than a staple crop but there is nothing else like tomatoes to replace them in my diet. They are also great container plants in temperate climates and are better suited to balcony gardening than a lot of other fruits are. My grafts were producing almost all year round in my windowsill granted they grew a good bit slower over winter. Winter fruit is always appreciated!

Any one else giving this a go and have any experience to share? Any Other rootstocks or techniques? Any critisims? Any questions? Any good links to add to my bibliography? Please leave a comment!

References for this writing:

My own experience/opinion/ideas

Grafting tomato (Solanum lycopersicum) onto the rootstock of a high-altitude accession of Solanum habrochaites improves suboptimal-temperature tolerance Jan Henk Venema ∗ , Boukelien E. Dijk, Joz ́ M. Bax, Philip R. van Hasselt, J. Theo M. Elzenga J.H. Venema et al. / Environmental and Experimental Botany 63 (2008) 359–367

The complete book of PLANT PROPAGATION by Robert C.M. Wright & Alan Titchmarsh ISBN: 0-7063-6412-0 (I can't find it online, it may be out of print) It is a great resource for all methods of propogation.