It’s a quieter time of year in the garden, and a good time to let ourselves and the landscape rest. For those of us who are always busy, it’s a good time for projects to prepare for the season ahead. One of the quirkier and most rewarding winter projects is dormant grafting, and it’s the kind of thing horticulturists get geeky about. Even if you aren’t the type to go nuts in a greenhouse, it might interest you to know that many trees and shrubs in your landscape are likely to be grafted. We love learning about our plants in a new light, and hope you will too.
What is Grafting?
Around the world, horticultural science creates many cultivated plants as we know them through a huge range of propagation methods. Grafting is a practice that involves joining two or more separate plants, most commonly the roots of one plant to the trunk of another, and is widely used on fruiting and ornamental trees, flowering shrubs, and conifers. Grafting is so common now that almost all fruit trees in the US horticultural trade have been grafted. And amazingly, this science is nothing new- evidence suggests that people have been grafting plants for the last 4,000 years.
So… Why graft? Besides the fact that it’s pretty cool to attach a Honeycrisp Apple to a Crabapple rootstock and watch it grow, there are real reasons why this is the horticultural go-to, even if it seems kind of weird. Ted Bilderback, Director of the JC Raulston Arboretum at North Carolina State University, gives the best possible explanation as to why anyone would go to the trouble to attach two plants together:
“[Grafting is usually done] because cuttings from the desired plant root poorly (or not at all). Also, these methods give the plant a certain characteristic of the rootstock – for example, hardiness, drought tolerance, or disease resistance.” Bilderback and his co-authors R. E. Bir and T. G. Ranney offer an excellent in-depth read on why and how to graft that we highly recommend to anyone interested. The diagram below is one of many from their publication.
Grafting can be incredibly simple or incredibly complex, depending on the plant material being joined. For whatever reason, some species just graft like a dream. Roses, for example, are notoriously easy to graft, while conifers are generally more difficult. The fact that it can be done at all is pretty incredible, considering that a successful graft means the complete joining of the two plants’ vascular systems. In order for this to be possible, the two plants must be closely related – You can’t graft a Peach onto a Maple tree rootstock, for example, but can graft it to a number of Plums, Apricots, and even Almonds – all within the same genus Prunus.
Shown above is a scion (a cutting of desired plant material containing a dormant bud) and a rootstock being joined. For the simplest grafts, just a wrap of grafting tape can be used. However, most grafts sustain best when grafting wax is also applied to prevent the union from drying out. If this graft is successful, the leaves that emerge from the scion’s bud in Spring will be the desired plant’s leaves, and eventually it will develop all of the surface characteristics of that plant, but it may also have hidden influence from the rootstock. For example, any variety of Apple, when grafted to a ‘Dwarf’ rootstock, will be shorter than it would be on its own – a great advantage for a small garden. A rootstock can also offer better resilience to diseases and improved absorption of water in a clay soil – both reasons for nurseries to sell grafted Dogwoods and Maples in the Bay Area, where our soil can be heavy clay.
Scions of the Times
Is this what’s behind those trendy fruit trees with 4 different kinds of Apples or Citrus fruits? You bet! While grafting is often invisible – most people have no idea that the trees in their yard or in their neighborhood park have been grafted – there are certain anomalies that are fun to play with. Grafting several related fruits together onto the same trunk is a very rewarding project or a fabulous score from the nursery, and either way makes a real conversation piece in the garden. To make things stranger, multi-graft trees are often grafted onto a trunk that is itself grafted onto a rootstock. That’s a lot of grafts.
As for non-fruiting trees that are grafted more than once, Weeping Cherries are a classic example. The “weeping” branches are often grafted to an upright trunk for maximum showiness, and that trunk grafted to a Wild Cherry rootstock that has disease resilience and hardiness in a range of soil types. Weeping conifers are often grafted in the same way. Pretty cool!
Caring For Your Grafts
Roses have become a much easier plant for Bay Area gardens since grafted rootstocks became the norm. Since we love roses, we consider this to be great news! One fact, however, is important to note when pruning your roses. Unlike a grafted tree, where you are unlikely to come into contact with the graft, a gardener giving their roses a hard prune may come close to the graft union (usually visible as a knob at the base of the plant.) It is most important not to cut below the graft, or the latent rootstock might begin to sprout, giving you some odd-colored blooms but also jeopardizing your prized rose (since rootstock is generally stronger than the desired rose, it might take over entirely after another season or two.) So keep an eye out for the graft union and try to keep your pruners away!
‘Stump’ sprouting or ‘Below-graft’ sprouting is a phenomenon just like it sounds. Common on grafted fruit trees, the rootstock begins sending out shoots and leaves from below the graft. Even weirder, sometimes these sprouts will emerge from the roots themselves, some distance from the trunk. If your tree is stump-sprouting, don’t be alarmed. Just cut off the sprouts as they emerge and be prepared to do it again next year. On the rare (but sad) chance that a recently-purchased tree begins to stump-sprout and dies back to the union, it’s no longer the tree you paid for even if it’s alive, so normally a nursery will offer to replace it.
Thank you as always for reading our blog! Wishing a Happy Martin Luther King Jr. Day to all of our readers.
“Even if I knew that tomorrow the world would go to pieces, I would still plant my apple tree.” — Dr. Martin Luther King, Jr.