When you buy a grapevine from a garden centre/nursery/online source you will normally be sold a grapevine that has been grafted onto a rootstock.
Grafting means that most of the upper part of an existing grapevine is removed and another vine (disease resistant) is united to the first one via graft union. The reason why grapevines are sold grafted in this way is to protect against Phylloxera, a disease that can affect the sap and roots of vines and which decimated commercial European grapevines in the past. If you grow vines from cuttings yourself these will be on the plant's own rootstock. For amateur use in the garden this is not critical.
Grapevine cuttings should be taken during the dormant season, normally the winter months of January and February here in the UK. If you take them too late you risk severe bleeding of several pints of sap from the parent vine and this will continue until the parent vine puts on new growth in the Spring.
You should take cuttings of well-ripened (brown) wood that grew out the previous season (smooth stems, not rough which indicates older wood). They should be approximately of pencil thickness and roughly 10 inches (25cm) long with, ideally, four buds.
You need to know, when planting the cuttings, which is top and which is bottom. If you always make a sloping cut to the top of a cutting (allowing water to roll off) and a flat cut on the base of each cutting, this will ensure you plant the right way up. Vine branches (canes) are often 6 to 8 feet long, so one branch can provide many cuttings.
When you insert the cutting in the compost, you should have two buds showing above the soil level. The lower two will make roots to sustain the new growth.
If you want to make an early start, you can grow cuttings on with bottom heat from a propagator which encourages the roots to grow. Cuttings can put on several inches of top growth without roots because inside the cutting is enough vitality to sustain this. But the sooner you have roots the quicker your cutting will get away and make some real growth
Alternatively, you can simply put your cuttings outdoors in pots with gritty compost and let nature take its course over the Spring and early Summer. If you have no pots, cuttings in the open ground will generally root, but you may have less success. My first attempt at rooting four cuttings in open ground gave me only one rooted vine. You will find that some vines grow quicker and more strongly than others. This year my Siegerrebe cuttings were the star of the show, reaching almost 4 feet by July from January cuttings.
The following video explains a method of growing new vines in the summner from semi-ripe cuttings. Success may vary on this, but it can be worth a try.
I have grown some cuttings successfully from softwood material in Southern England. Unlike the video above which shows semi-ripe wood for cuttings, I used soft tip growth in May, approx 6 inches (15cm)long, with just one leaf and the growing tip left on the cutting. For a growing medium I used (a)compost in one and(b)vermiculite in the other. Both sets of cuttings were treated identically. A clear plastic bag was secured on top of the pot, to retain moisture. No rooting compound was used. During the day they were in a shaded part of my greenhouse, up to approx 30 degrees C (86F). At night I put them in the top of my airing cupboard above the boiler, so very warm here too. The cuttings in compost soon became affected by mould, so were discarded. The ones in vermiculite were fine and produced a good set of roots in 4 weeks, when they were potted up.
Layering involves training a section of an existing vine down to ground level so that the stem is pinned to the ground and comes up again. The section in the ground is left until the following year by which time it should have produced roots from the section under ground. In early Spring you can check that roots have formed, then sever the rooted section from the parent part of the vine and hey presto you have a new rooted grapevine!
It is possible to propagate grapevines from seed but it is a lengthy process and, more importantly, the resulting vines will be genetically different to the parent vine. If you grew 100 from seed you MIGHT get a new variety, but quite honestly it's not worth the trouble! Grape seeds used in this way need stratification, which is a long word meaning they must have been exposed to cold winter weather to condition them to become viable to produce new plants in the Spring. Also, grape seeds put in water for 12 hours will reveal to you which ones are viable. Only use the ones that sink, are dark brown and hence are viable. It can be fun seeing your little baby vines sprouting, but not worth the trouble long term for the reason stated.
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