Most mulberry species and cultivars are relatively easy to propagate by conventional means. There are an abundance of Youtube videos and internet guides that give good instructions on growing mulberries from cuttings and seed, grafting, and air layering. But what works for one species or cultivar, may not apply to another.
Harwood Cuttings: If you want to propagate a Morus alba cultivar, you're in luck; most can be propagated simply by sticking a 6" to 8" cutting (dormant, or from a cutting in spring or summer, after first removing the leaves) half-way down into a pot of a well-draining "soilless" mixture. I have had good success with a mixture of 1/3 sphagnum peat moss, 1/3 vermiculite, and 1/3 perlite, but Bass Samaan, owner of "Trees of Joy" has been successful propagating "difficult to root" 'Illinois Everbearing' using just vermiculite and rooting hormone. Keep the cuttings in a shaded location, free of direct sunlight until well rooted (40-60 days). Water as needed. Pot the rooted cuttings in good potting soil and leave shaded for another week. Gradually expose the plants to more sunlight.
Some mulberry cuttings require even less care: Some cuttings will root and grow just by sticking them in the ground anywhere in the yard; even cuttings from plants in spring and summer, by stripping off the leaves when taking the cutting (or remove all but one or two partial leaves trimmed to ~ 1/2 credit card size).
Morus nigra, Morus macroura, and Morus rubra (and hybrids) are more fastidious and usually require a clear plastic bag (or plastic liter soda bottle with its bottom cut off) over the cuttings to conserve transpiration. Cut a dime-size hole after four weeks. Observe closely for a couple of hours after cutting the hole for signs of wilting, and if it starts to wilt, immediately cover the hole. Continue cutting dime-sized holes every week, if no wilting occurs. Make sure that the cuttings never get exposed to direct sunlight throughout the whole day, as this will cause a "greenhouse" effect and kill your cuttings.
Cuttings may benefit from dipping in a rooting hormone prior to planting, and fungicides (alone or in combination with rooting hormones) have shown promise. Onion juice works surprisingly well. Cinnamon and honey are natural fungicides and cuttings dipped in cinnamon powder or honey before planting are said to aid survival (But I haven't had luck with them). Rooting success is often quite low, so your best option may be to plant several cuttings using several methods.
An "old-time" method for rooting Morus nigra at a higher level of success: Where you want a mulberry tree to grow, dig a 6" to 8" deep trench, long enough to accommodate a two to three-foot dormant cutting. Lay the cutting in the trench and, while bending the tip of the cutting carefully so that 4" will be above the ground surface, fill the trench with soil.
A study from the University of Duhok, Department of Horticulture in Duhok, Iraq (1) obtained 80% rooting success of hardened Black Mulberry (Morus nigra) cuttings by using 14-16 mm diameter cuttings and 4000 ppm IBA rooting hormone. Cuttings were taken in February (I assume dormant cuttings), were 18-20 cm in length, and were buried 2/3 of their length into sandy soil and placed in air conditioning (The study didn't address lighting requirements). Morus nigra is one of the most difficult mulberry species to root using cuttings (true Morus rubra and the cultivar 'King White Shahtoot' could be even more challenging), so perhaps this method will obtain good results with an array of different species and cultivars.
Softwood & Semi-hardwood Cuttings: Most mulberry cultivars can be easily propagated by softwood cuttings at a very high success rate, and is useful for propagating the more difficult cultivars that don't respond to propagation by hardwood cuttings.
Summer cuttings of new growth, when the stems are still mostly green, seem to "strike" best. Take 6" to 10" cuttings and strip all the leaves except the top leaf or two (cut leaves to manageable size if they are very large). Dip the end in rooting hormone (hormones help but are not essential...I use Clonex) and stick a third way down into a good growing medium (coconut coir, vermiculite, or a good potting soil). Water well and then cover with a plastic soft-drink bottle (with the bottom or top cut off) or clear plastic bag or anything that will create a "humidity dome". The "dome" should not be completely air-tight. A pea-sized hole or two should be cut into plastic bags, but soft-drink bottles are OK, since some air seeps in from where the bottle rests on the soil. It is imperative that the cuttings are kept shaded and are never exposed to direct sunlight (even for a couple minutes).
Cuttings should be well rooted in 4 to 8 weeks; then gradually allow more fresh air to enter the "humidity dome".
Silk Hope softwood cuttings
Seed: Growing mulberries from seed may be an interesting attempt to create a new cultivar, but it has its disadvantages. Mulberries do not grow "true to seed", so your new plant may not be like the mother plant. Also, mulberries are generally dioecious (having male and female flowers on separate plants), with a low percentage of plants being monoecious (having male and female on the same plant). And then there is the issue of time; mulberries grown from seed can take up to ten years to produce fruit (Morus nigra can take even longer). And when it does fruit, it can take several years before the fruit reaches its maximum size and abundance. But seedlings are an easy way to produce rootstock for grafting.
Most Morus alba and Morus rubra seeds planted 1/8" deep in a seed starter soil or potting mix, will germinate in about three weeks at about a thirty percent germination rate. Stratification for 30 to 60 days may increase germination percentages but does not appear necessary. Morus nigra is claimed by some authorities to not be able to produce a viable seed, perhaps as evidenced by the seeming lack of "wild" offspring. But that could be due to most Morus nigra trees are propagated as female clones, with few male pollinators. "Scientific" papers exist on the internet which show Morus nigra seeds are viable (2). Another factor which may contribute to seedling scarcity is that Morus nigra seedlings seem to have great difficulty growing and thriving for their first few years.
Morus nigra seedlings
Dithmar Guillaum, a Belgium nurseryman, grows several hundered mulberry seedlings a year for grafting rootstock. This is his tried and tested method:
"The seeds are dried and stored at 4°C untill spring. I sow the dry seeds without any treatment (no soaking or any other treatment). They are sown indivdually in microtrays with cell size about 1.8 x 1.8cm and +/- 4cm deep. (18 x 32 cells per tray= 576 cells). I use very fine sieved substrate and sow one seed in each substrate filled cell, a very tedious job….I then cover all the cells with a very thin layer of very fine cocopeat. After carefully watering the trays (spraying) and letting drain the surplus water I wrap them in cling foil to keep the moisture in and I place them on the shelves of a rack in the greenhouse. No bottom heat… just fluctuating greenhouse temperature: +/- 10°C at night and +/- 22-28°C during the day. The trays are exposed to the natural light in the greenhouse. The seeds usually start to germinate within 2 weeks but germination can be rather erratic and some seeds will take 4 weeks to germinate. Germination percentage is usually around 75%. I transplant the seeds into individual 50cc pots when they are about 5cm tall."
Grafting: Mulberries cultivars that are difficult to propagate by cuttings can be grafted onto Morus alba or Morus rubra seedlings or rooted cuttings (Morus alba rootstocks will generally give higher rates of success than Morus rubra). This author has had very good success with just simple "splice grafting". There are some important steps to take, though:
1st: Mulberries "bleed" sap profusely when cut and the excessive sap interferes with proper healing of the union between the rootstock and scion. Better success can be obtained by making a small perpendicular cut an inch or so below the intended graft location to bleed off some excess sap prior to grafting.
2nd: Your rootstock and scion must be the same diameter.
3rd: Cut your scion first and immediately submerge the cut end in clean water. Removing all but one or two buds on your scion will increase survival odds.
4th: Cut the rootstock and immediately put a few drops of water on the cut (the exposed cuts must not be allowed to dry out for more than a couple seconds).
5th: Place the two parts together and wrap the joint with Parafilm® Grafting Tape. Then wrap the joint again with vinyl electrical tape to pull the two parts together tightly (don't get any electrical tape on bare bark, because it will strip the bark when you remove it a couple months later).
6th: Wrap the rest of the scion with Parafilm® Grafting Tape. Only allow a single layer of tape over the buds (the new growth will push right through the Parafilm). 7th: Cover black electrical tape with either a piece of aluminum foil or more Parafilm® Grafting Tape to reflect excessive sunlight (not necessary when using lighter vinyl tape colors).
For inexperienced grafters, very good success rates can be achieved with the use of a grafting tool (Zenport ZJ68 V-Cut Top Grafting Tool has good reviews).
Cleft grafting; A nurseryman in Belgium who performs a thousand or more grafts a year outlines his technique:
"For mulberry I find a simple cleft graft to be the most effective provided that cambium layers really, really match up perfectly at least on one side of the graft. I also allow some new growth on the rootstock so the new tree can regain strength while the graft is healing. When the new graft is actively growing I remove the growth on the rootstock permanently. I sometimes also use whip and tongue but this method seems to be less successful…The rootstock I use is always Morus alba, medium to small caliper. The smallest ones I graft are one year old container grown seedlings of about 3mm diameter up to field harvested 2 year old seedlings 15mm diameter. I prefer elastic bands in combination with wax because I find that this combination allows the graft to breath a little bit. Buddy tape really seals the graft airtight. When the callus is forming the elastic band or buddy tape stretches along with the growth of the callus so no need to cut the elastic or remove the buddy tape."
Bark grafting also works well for mulberries, when your rootstock is larger than your scion. "Veneer grafting" when the bark is "slipping" may work also. (Video)
Root grafting can be used to created a mulberry tree on its own roots. Root grafts on mulberries will be most successful with pencil diameter root pieces that are a minimum of eight inches in length. Binding the graft union with several layers of vinyl tape will constrict development of the root and force the grafted mulberry scion to develop its own roots (providing that the graft union has been buried sufficiently deep).
Mulberries can be grafted from late winter through summer (some cultivars are difficult to graft in summer months, especially Morus rubra), but when grafting after the weather has turned warm you must keep direct sunlight away from your budding scion for a couple months. Mulberry scions can be obtained well in advance of spring and stored in a Ziplock bag in a refrigerator, so as to be on hand when the rootstock begins to bud (Actually, I have had my best success grafting when the rootstock is dormant...contrary to most authorities stating to graft at the break of dormancy).
Air Layering: When all other methods prove unsuccessful, "air layering" is a very reliable way to propagate mulberries. Air layering is done on either last year's growth or, in summer, on fully "hardened" growth. Most mulberries will form enough of a root system that will allow for removal from the mother plant in three months (but check before cutting). After removing from the mother plant remove all but a couple leaves, and if those are large, cut in half with scissors. Plant in good potting soil and keep shaded for a couple weeks.
Occasionally the leaves on an air layered branch will wilt before the air layer root ball has formed. This can be caused by rot from an excessively wet rooting medium, or too dry a rooting medium, but often for no apparent reason. My interpretation of this phenomena (which may not be accurate) is that the tree is aborting that branch since it is no longer providing sugars to the rest of the tree. If this occurs, remove and examine the air layer; if some roots or even just callousing is visible, remove the wilted leaves and pot up the air layer in good potting soil, and the air layer will often bud out with fresh leaves and grow in a few weeks.
More grafting advice from Dithmar (Belgium nurseryman)
"I presume we are talking about container-grown rootstock.
There are always a good number of grafts that will fail…
Ideally, you should use 2-year-old field-grown rootstock. After lifting the dormant rootstock all the fine roots must be washed clean of dirt and cut back until you are left with just the basic root structure. The stem is cut off at about 15 -20cm above the root collar and grafted with the desired variety (cleft graft). The rootstock is potted. It is best to keep the grafted mulberry relatively cool for the first few weeks. When you see the buds of the graft swelling it does not mean that the graft has taken! Normally some wild growth will start to form on the rootstock…just let it grow and cut it back a bit if it grows to fast. Normally the buds on the graft will also start to break open but soon growth of the graft will probably stop.
The reason for this is the strong sap flow of the rootstock that will eject the graft and prevent it from forming callus. This is the reason why it is best to use rootstock with trimmed roots…to reduce the sap flow…and leaving wild growth on the rootstock will make it possible for the rootstock to evaporate and photosynthesize and alleviate the pressure of the sap flow. All of this is necessary to keep the graft alive. Normally the graft should stay green after bud break but it doesn’t leaf out or it shows only some stunted growth. The idea is to keep it in that state until enough callus has formed. When callus has finally formed between graft and rootstock you can trim off the wild growth of the rootstock and as a result, the graft should soon leaf out and grow vigorously. Cutting off the wild growth is done after about 5 to 6 weeks.
Of course, when the weather turns hot too soon this will not help the healing of the graft because it will induce stronger sap flow which will eject the graft while at the same time the graft will also more easily desiccate."
"When grafting mulberries in the field you should use the same grafting technique and also let the wild growth form on the rootstock until it is no longer necessary…
Another important factor in grafting mulberries is the variety. Some varieties will graft very easily while others are almost impossible to graft. Most often this has to do with callus formation and it is just a fact that some will easily form callus and others will not. These are the same mulberries that will easily root or almost not root at all."
1)The Effect of Auxin IBA and Kinetin in Budding Success Percentage of Mulberry (Morus sp.), Sulaiman M. Kako,
Int. J. Pure Appl. Sci. Technol., 13(1) (2012), pp. 46-52
2) BREAKING SEED DORMANCY IN BLACK MULBERRY (MORUS NIGRA L.) BY COLD STRATIFICATION AND EXOGENOUS APPLICATION OF GIBBERELLIC ACID; FATMA KOYUNCU