CONIFER PROPAGATION 101
So, you’ve been bitten by the conifer bug and have your own collection of these wonderful plants and you’ve entered the Cone Zone by joining the American Conifer Society. You may also be following conifer forums, groups and blogs on the ACS website ,Houzz, Facebook, and who knows how many other places and your doctor has confirmed that you have ACS or "Addicted Conifer Syndrome." Fortunately there is a cure: acquire more conifers! But wait, this can cause a side effect known as USS or "Upset Spouse Syndrome," when your partner discovers the drain to the communal bank account! What’s a Conehead to do? Propagate, my friend; that is the answer. No, no, not that! I mean propagate your own conifers. This timeless skill is easy to acquire, costs very little, is great fun, and the end result is more conifers. Life just doesn’t get any better than that!
There are many different techniques of plant propagation including seed, cuttings, grafting, layering, tissue culture and others, but conifers are generally propagated by the first three techniques. In this two part article we will give a brief synopsis of these techniques, discuss when each one is appropriate to use, and cover how to perform them in your own home and garden.
What Technique to Choose
Deciding whether to propagate a conifer by cuttings, seed, or grafting becomes easier if we first divide the techniques by their type of propagation. By this we mean whether or not the technique is considered vegetative propagation. Once that has been determined, you can select the appropriate technique to give you the desired results.
Seed propagation is not considered a vegetative form of propagation and the genetic material within a seed is a mix of the DNA from the plant bearing the seed and the DNA from the plant that pollinated the embryo that becomes the seed. Therefore when the seed germinates, it creates a plant that may be similar to its parents, but will not be genetically identical. Basic biology 101, right?
Cutting and grafting propagation are vegetative forms of propagation. In other words, a vegetative portion of the parent plant is removed and in some way induced to produce its own roots (as in a cutting) or attached to an existing root system (as in grafting). This vegetative portion of the parent plant retains the exact same characteristics of the parent plant and is simply growing on a new set of roots. With this division of propagation techniques in mind, if a new plant exactly like the original is desired, then choose a vegetative technique. If diversity is desired, then choose seed propagation. Now, on to the meat and potatoes portion of our article.
Seed propagation is the easiest technique to use and requires nothing fancy. You collect the seed. You sow the seed. And you wait. That’s all there is to it . . . sort of.
Knowing when to collect the seed is important since seed collected too soon may not be mature and waiting too long to collect seed can mean its loss to wind and wildlife. Generally speaking a color change in the seed bearing structure is a good indication that the seeds are ripe and ready to collect. A seed bearing structure on a conifer can have many fancy names, but for simplicity’s sake in this article, we will use the terms cone and berry to distinguish between the two general types of structures.
A cone includes the typical cone structure that we are all familiar with on a pine or spruce, as well as the non-typical cone like structures on plants such as arborvitae or cypress. These non-typical cone-like structures are not fleshy like a berry, but can be round or other shapes and when ripe, they will open up for the wind to disperse their seed like a typical cone will. The berry type of seed structure has a fleshy covering that is intended to attract birds or other wild-life to “collect” it, devour the fleshy portion and then deposit the seed in a new location. Conifers that have this type of seed structure include yews, junipers and others. Observing these seed bearing structures as they grow and mature is quite fascinating (Although time consuming in the case of a juniper that can take several years from fertilization to maturity!). At blooming time, they can be quite colorful and give a seasonal splash of color to your favorite conifer. After fertilization the structures generally change to a green or nondescript color and stay that way while the seeds develop. Once the seeds reach maturity the structure will change color to what we typically think of as mature. The cone types may change to a brownish or grayish hue while berry types may change to a red, blue or other color that indicates to wildlife that they are ripe and ready for the pickin’. This is the point for you to do your pickin’ as well. Once you’ve collected your cones and berries, you need to extract the seeds. If you’ve collected cones just after they’ve changed color but haven’t opened up yet (which is usually the ideal time for collection), you’ll need to dry them so that they open and release their precious cargo. Placing them in a paper bag and putting the bag in a warm, dry area such as on a heat register or in a sunny window works well. Once the cones have opened up or broken apart, they can be shaken or tumbled to release the seeds. The seeds can be quite tiny and dust-like or large and plump, so take care to not lose them!
Seeds contained within berry-like structures can be released by rubbing them on a screen with running water or mashed with your fingers to separate the seed from the flesh. Be prepared for some staining on your fingers! After cleaning, the seeds should be rinsed, then slightly dried so that they can be easily handled. Sowing the seeds is as easy as falling off a log, only safer. Some, but not all conifer seeds require what is known as a period of stratification. Stratification is an interval where the seed is surrounded by a cool, moist medium (Soil) during which it will undergo internal biological changes to prepare it for germination. In nature the need for stratification is met by winter soil conditions. Even though not all conifer seeds require stratification, it is easiest to simply sow the seeds in the fall and let them be exposed to normal winter conditions. No harm will come to the seeds if they are a type that doesn’t require stratification, and the stratification process may help improve germination.
You can sow seeds directly into garden soil during the fall or in typical potting soil in pots or flats. In either case the need to protect the seeds from marauding rodents is essential! The seeds should be sown and covered with fine soil to a depth that is roughly equal to the diameter of the seed. Some extremely fine seed may be best sown by placing it on top of the soil, watering it in and then covering the flat or pot with a piece of glass or Plexiglas to maintain high humidity at the soil surface. Be sure the covering isn’t actually touching the soil surface. Now the easy part………… we wait.
With a bit of luck and no roving bands of rodents, your seeds should germinate in the spring. Please note however, that sometimes the seeds can be very slow to germinate and may actually germinate gradually over the next year and even into the following spring. Patience is key. It can be quite fascinating to watch the seedlings emerge and change from unrecognizable plants into something that actually looks similar to the plant from which you collected the seed. Imagine that!
In part I of this article we discussed that conifers can be vegetatively propagated by cuttings or by grafting. But how do we know which technique to use and for that matter, what is cutting propagation and what is grafting?
We’ll answer the second question first. Cutting propagation, as mentioned before, is the removal of a vegetative portion of a parent plant (Typically the end of a healthy branch which is called a cutting), and inducing it to form its own roots. We’ll get into the details of how in a bit. Grafting is a technique where a similar vegetative portion of a parent plant (known as a scion) is removed and affixed or “grafted” to a seedling (known as a rootstock) with an existing root system. The two knit together and eventually the top of the seedling is removed leaving the new scion to grow on its own using the seedling roots.
Now, back to the first question: How do we know which technique to use? This is where a little research may be in order. Almost any conifer can be grafted, but not all can be rooted. Cuttings are the easiest and simplest of the two techniques and are generally the first choice if the plant can be successfully rooted. Using the internet and textbooks (you remember those, right?), you can research if your conifer can be rooted by cuttings. conifers that are generally relatively easy to propagate by cuttings include: Arborvitae (Thuja), False Cypress (Chamaecyparis), Juniper (Juniperus), Yew (Taxus) and for people with the magic touch: Hemlock (Tsuga), some dwarf spruces and even some pines. For plants that cannot be propagated by cuttings, grafting becomes the preferred choice.
Propagation by Cuttings
Propagation of many conifers by cuttings can be done with semi-hardwood cuttings. This term refers to the fact that the cuttings are no longer actively growing, but have not yet gone fully dormant for the winter. Semi-hardwood cuttings are good for Chamaecyparis, Thuja, and Taxus selections while Junipers may best be done by hardwood, fully dormant cuttings in December and generally require a greenhouse with some way to heat the soil. Semi-hardwood cuttings are collected in September or early October and stuck in a sand based media in a cold frame, greenhouse or even just a pot covered with a plastic bag and placed in a cool location. The cuttings will develop roots during the fall and following spring.
A 50/50 mix of sand and peat moss or sand and perlite makes a good rooting media to stick your cuttings in. If this is not available, potting mix can be utilized, but you will need to be careful to not over-moisten the media which can rot the cuttings. The media can be placed in a pot or tray and should be moist but not wet.
Collect strong, healthy, 4 to 8 inch long (a dwarf plant may only provide cuttings that are 1 to 2 inches long) cuttings from the current season's growth. Prepare the cuttings by removing the lower 1/3 of the needles and/or branches from the stem and make a fresh cut on the basal end of the cutting. On most conifers, make a thin slice or wound on one side of the cutting. The wound should be about 3/4 inch long, and extend from the basal end upward. This wound will encourage stronger root development on conifers. The finished cutting should be 3 to 6 inches long (smaller for dwarf plants). Dip the bottom 1 inch of the cutting in a rooting hormone powder, gel or liquid solution. Rooting hormones are readily available online or at larger garden centers and nurseries.
Stick your prepared cuttings in the moist media and firm the media around the cutting with your thumb and forefinger. You may want to dibble a hole for the cutting with a pencil or nail to make insertion of the cutting easier and to prevent removing of the hormone. Be sure the base of the cutting is positioned above the bottom 1/3 of the media in the container. The bottom 1/3 of the media in a container contains more water than air and will inhibit rooting and promote rot. After sticking, water in the cuttings and cover them with something clear to maintain high humidity. Cuttings kept in a greenhouse or cold frame may need to be shaded until winter to prevent overheating during the fall.
If a cold frame or greenhouse is not available, place the cuttings in a bright but shaded location that is protected from the elements. A south facing window in a cool garage or shed might work well.
Inspect the cuttings often during the fall. Do not let the media dry out; water as necessary. Remove any dead or diseased foliage and cuttings as soon as they appear. Check the cuttings periodically during the winter and keep the media moist. Some cuttings may root by winter, but many will root the following spring. As the weather warms up, be sure the cuttings do not get overly warm. Once rooting has begun in the spring, ventilate the cuttings as necessary to acclimate them to lower humidity. However, be sure not to ventilate the cuttings until they have established roots. They will desiccate if the humidity is too low and they don’t have any roots to draw up moisture. When the cuttings begin to root and grow, and all danger of frost is gone, place them in a shaded area until they are ready to plant. Watering them with a mild liquid fertilizer solution will encourage further root and top growth.
Propagation by Grafting
Grafting refers to the insertion of a small branch, called a scion, into the bark of a plant of the same genus. The internet and propagation reference books are great resources for finding information on the grafting of conifers and woody plants in general.
Grafting of conifers is typically performed indoors during the months of January and February. A greenhouse provides the best results, but grafting can be done in a basement provided that an enclosed area with moisture, light and heat is available. There are many different types of grafting, but the one that will be described in this article is called pot grafting. Pot grafting is a common technique for Japanese Maples, most conifers, dogwoods, European Beeches and others. Grafting consists of a root stock, scion, the carpentry of joining the two, and the necessary care of the plant before and after grafting.
The grafting process actually begins a year or more before the grafting will occur with the purchase or propagation of the necessary root stocks. Root stocks are healthy young seedlings of plants of the same genus as the plants to be grafted on them. There are exceptions to the same-genus requirement, but for the most part, the scion and root stock should be of the same genus. Propagation reference books contain lists of scions and their recommended root stocks.
Ideally the root stock should to be approximately the diameter of a pencil at the time of grafting. Purchasing one- or two-year old bare root seedlings and potting them up in the spring will typically yield a root stock of the required size by winter. Some nurseries also sell root stocks already potted and ready to graft.
Grafts and their subsequent success are only as good as the root stocks they are placed on. Therefore, select strong, straight and well rooted seedlings. Pot the seedlings in containers that have enough room for root growth, but are not too large to handle during grafting. A pot that is 2 to 4 inches in diameter and 4 to 6 inches deep is usually adequate. Keep the potted root stocks watered and fertilized during the summer so that they enter dormancy as healthy as possible. Older seedlings with thick trunks do not make good root stocks unless you will be making high grafts at the top of the seedling.
Allow the root stocks to go dormant naturally in the fall and store them in a cold frame or other accessible, but protected area until it is time to graft.
The best scions are cut from healthy branches of the previous season’s growth. A terminal branch generally yields the best results for the graft and subsequent growth. Two year old wood can be used if the scion is very small such as on some dwarf conifers. Scion wood for winter grafting should be collected when it is fully dormant.
Collect the scion wood as close as possible to the time that you will be performing the grafting operation. It is usually best to collect the scions on a day where the temperature is above freezing. If the scions need to be stored for a while before grafting, then wrap them in moist paper towels and place them in a reclosable plastic bag. Store the bagged scions in a refrigerator below 40ºF but above freezing. Storage above 40ºF may not keep the scions fully dormant. Be sure to label your scions so that you’ll know what variety they are when you graft.
The pot grafting technique that will be described here is called side grafting. There are many other techniques for grafting that can be used as well and these are explained in various propagation reference books.
Two to three weeks before you will be grafting, move the root stocks into a greenhouse or heated area to begin forcing root growth. Be sure to not let the root stocks dry out in the heat. You do not want the potting media to be dripping wet, just moist.
Too much water in the pot can be harmful at the time of grafting due to excessive sap in the graft union. Root stocks are ready to graft when the ends of their roots are showing new white tips of growth.
While the rootstocks are being heated, sort through them and remove any weak, deformed or otherwise undesirable seedlings. Clean the lower 3 to 6 inches of the seedling’s stem. Remove any branches, needles and dirt within this area. Cleaning the outside of the pot will help keep your hands clean during the grafting process.
When you are ready to graft, assemble your root stocks, scions and equipment at a comfortable work station. Cleanliness is important during the grafting operation. The grafting knife should be extremely sharp and clean. Periodically clean the knife and any other cutting instruments with alcohol. The use of finger safety tape on any fingers that could contact the sharp edge of the grafting knife is recommended.
Prepare the scions for grafting by removing any needles or branches on the lower 1/3 of the scion.
Select a straight, blemish and wound free section in the lower 4 inches of the root stock stem to make your first cut. All cuts on the scion and root stock should be made in one, smooth motion. This will yield the best surface for mating the scion to the root stock. Make the first cut in a downward direction to create a small flap on the stem of the root stock. Do not cut this flap off. The width of this cut should be as close to the width of your scions as possible, while still penetrating the bark of the root stock.
Make two downward cuts on the scion, one on each side of the scion. Make one angled cut at the end of the scion to trim the cut surfaces to length. The length of the cuts should be equal to the length of the cut made on the root stock.
Insert the scion into the root stock, aligning the outside of the scion with the edge of the cut on the root stock. Ideally both sides of the scion should align with both sides of the cut on the root stock. If they do not, then align one side only. Close the flap onto the scion, aligning its edges with the edges of the scion.
Tie in the scion with a rubber strip that is meant for tying in grafts. These are available from most companies that offer grafting supplies. Do not pull the strip excessively tight, but tight enough to firmly hold the scion to the root stock. The wrapping of the strip should start and end above and below the cuts.
Coat the union area with wax. Specialized grafting wax can be used as well as ordinary paraffin wax or beeswax that is heated just above the melting point. Conifers require high humidity while the scion is knitting in. Covering the grafted plants with a sheet of clear plastic works well. Covering the individual grafted plants with a clear plastic bag is also effective.
Aftercare of the Graft
Move the grafted plants back to the area where you preheated the root stocks. Warm roots (65 to 70°F) while keeping the tops cool (50 to 55ºF) is best. However, if this is not possible, then keeping a steady 55 to 65ºF is the next best option. Air temperatures above 65ºF can force the scion into to growth before the union is knitted and lead to possible failure. Keep the media in the pots moist but not dripping wet. However, do not let the media dry out as this is a critical time for the knitting graft. The plants need plenty of light, but direct, intense sunlight can dehydrate the scion. Keeping the humidity high in the growing area will help the scion survive until the graft union is knitted.
After several weeks, the scion should show some signs of growth. Ventilate the cover at this time and cut back about 1/3 of the root stock. After about 3 to 4 more weeks, the scion should be in full growth and the plastic covering can be removed. At this time cut back another 1/3 of the root stock. If the scion is growing very well, you may take off all the root stock at this time but many conifer grafters prefer to leave a small portion of the rootstock with some needles and a branch or two on for the next year. This is especially true for very dwarf conifers where the scion will not be large enough or strong enough to support the root system.
By mid to late summer or possibly by the following spring, the graft will be ready for potting up or planting in a protected area. After potting or planting, remove the rubber strip from the union. This is important to prevent possible girdling of the trunk by the strip. Grafted plants that are not a dwarf type will probably need to be staked for the first couple of years to establish a straight trunk.
Now that the secrets of conifer propagation have been revealed to you, there is nothing stopping your collection from growing. Except the police if you are caught stealing cuttings or scions from your local arboretum. That would result in a whole new problem with your spouse that is not covered in this article! Above all, enjoy your conifers, give propagation a try, and don’t be afraid to reach out to your fellow cone heads for advice.
Editors’ note: Ted Hildebrandt is a principle of Coldwater Pond Nursery and experienced grafter, producing many fine conifers which he generously donates to annual meeting auctions.
Excerpt from the Winter 2016 Northeast Region Newsletter. Gain access to archives of past newsletters and the National Conifer Quarterly by becoming a member of the American Conifer Society.