Holly selections for ornamental uses are propagated almost entirely from cuttings. This is because seed is slow to germinate and young plants are often different from the parents in fruit and foliage. Since rooted slips or cuttings produce young plants with the same characteristics as the parents, vegetative reproduction is employed to perpetuate choice varieties.
Nurserymen are propagating American holly (Ilex opaca) on a commercial scale, and prices for well-rooted stock arc reasonable. The amateur gardener, however, occasionally wants to root a few plants for his own pleasure, but does not know how to go alxnu it. A few simple rules, carefully followed, will insure success.
Hollies vary in their ability to produce roots from cuttings. Some root easily, others do so with great difficulty. Therefore, it is impossible to predict with accuracy the percentage of cuttings that an amateur may anticipate, even under most satisfactory conditions.
First of all, select wood that is mature. In central New York, during the past five years, the current season wood of American holly was matured sufficiently for rooting by September I. Cuttings of current season wood, year-old and two-year-old wood taken during September, October, November and December rooted successfully.
In the north, it is desirable to mot cuttings in the fall and early winter, since they can be transplanted in the spring and not be carried over a second season indoors. Tips of vigorous primary and sec ondary branches are best. Freshly cut twigs should be used immediately or placed in water if they are to be held overnight before planting.
Five-inch cuttings, with three to five leaves, arc easy to handle and satisfactory for rooting. Frequently two such cuttings can he obtained from a branch tip. The bottom end of a slip may be cm. directly across or at a slight angle and the bark left intact or lightly wounded. Dip the base of each slip in a suitable hormone (such as Hormodin No. 3) before inserting in the rooting medium.
When inserting the slips, set them vertically, about two inches deep, and space approximately two inches apart in the moist substratum. Crowding is not detrimental and, in fact, assists in retaining high humidity. When rooted, the best procedure is to remove the cuttings before the young roots become matted.
A standard sized seed flat makes a good rooting chamber. The area above the rooting medium may be increased by simple lath frames, set upon the other, and lopped with a pane of glass. The chamber need not be airtight. Semi-coarse vermiculite is an excellent rooting medium. It retains moisture, yet provides good drainage; it does not pack, and therefore allows good aeration; it permits rooted stock to be removed for potting without root injury. Fill the seed fiat to the top with vermiculite, firm lightly and wet thoroughly.
After the rooting chamber is filled with cuttings, water well and put the glass pane in place. Daily watering is essential, and allowing cuttings to dry out can be fatal. Room temperature will suffice, although rooting will be hastened if bottom heat is provided. Though direct sunlight is not necessary for holly, the rooting chamber should be kept in a well-lighted location.
Within three to six months, the cuttings should have abundant roots and may be replanted in pots, bands or flats of soil containing a high percentage of peat moss. It is desirable to prune long roots rather than to crowd them into small containers. By this method approximately 85 per cent of the cuttings Ôill root, while 100 per cent is not unusual.
Controlled experiments have shown that the application of foliage fertilizers to cuttings in the rooting chamber may be detrimental to some selections of holly. Other selections respond to foliage fertilizers by producing unusually good root growth. This phase of propagation needs careful study. Also, year-old wood has seemed to produce sturdier roots than current season wood.
During late spring or early summer, the young rooted plants may be reset in a nursery plot, provided with proper backfill and deeply mulched with light organic material. Mulch guards against summer drought and winter freezing to a depth below the root system. Some growers prefer to carry the young plants over for an additional season in a coldframe, which is a good safety measure.
Fertile, Acid Soil
Holly likes a fertile, sandy loam, somewhat on the acid side. For backfill I use mixture of approximately equal parts of garden loam, sand and wood mold from old chestnut stumps, fertilized with cottonseed meal. For a mulch, alternate layers of oak leaves and coarse sawdust are excellent. Cottonseed meal is added each spring as an organic source of nitrogen. In the north, it seems best not to force excessive growth, since fully-hardened wood can better withstand low temperatures without injury.
Selections of American holly (Ilex spare), English holly (I. Aquifolium) and Japanese holly (I. crenata) have been reproduced by cuttings and grown in the open for the last several years at Syracuse, New York, where winter temperatures have dropped below – 10¡ F. for several consecutive days and nights. Young plants of American holly, with thoroughly hardened wood in the fall, have been surprisingly free of winter injury, even at – 20 degrees F. They have bloomed each spring and set good crops of berries.
English holly selections set their flower buds in the autumn, and these may be killed during the winter by extremely low temperatures. However, plants have flowered with us after relatively mild winters. Japanese holly forms flowers and produces its attractive black fruits each summer.
I also have several specimens of Burford holly (flex cornuta burfordi) in 5-inch clay pots, which are sunk in garden soil each summer and kept in a basement playroom during the winter. By early April, they come into bloom and fill the room with their pleasing fragrance. To assure abundant fruiting I use a hormone spray, even though fruit will set in some quantity without it. Sometimes, after moving to the garden, a second period of bloom occurs.
I have had no success in producing native holly seedlings outdoors. Even though the seeds survive winter cold and germinate in the spring, the seedling root system seems too shallow to reach below the frost line in order to meet the first winter needs of the evergreen foliage. Perhaps this explains in part why American holly has not spread naturally into cold areas, even though established plants can endure low temperatures.
In my experiences, pests on holly have been rare. The holly leaf miner came in accidentally on some planting stock and spread to established plants. The following season DDT was used, and the leaf miner was eliminated. With leaf miners absent, the leaves are free of the disfiguring punctures associated with the feeding habits of these insects. Mites have not been troublesome, and no fungus pests have appeared.
Robins have been no problem, because berries turn red after the birds leave in the late autumn. Although the fruits frequently persist until the following slimmer, robins have not used them as food in the spring. Thus it is not unusual to have the old red berries overlap the young green fruits of the current season. Plants do suffer from some breakage from heavy, wet autumn snow. To eliminate or reduce this hazard, snow should be removed before its weight is sufficient to break the branches.
I have not lost established trees of American holly because of low winter temperatures. Some small newly set plants have been killed, apparently because their roots were shallow and the mulch was not sufficiently deep to protect them. A few of the newly planted trees that died to the ground over winter sent up new sprouts the following spring.
Some choice selections of American holly fruit when young include Old Heavy Berry, which set rich sprays of berries when the plants were three years old. Arden and St. Ann have fruited also when relatively young.
If you like holly and have a somewhat sheltered spot in semi-shade, the chances are favorable for growing some of the many hollies where temperatures drop below the zero mark. It is wise to let a specialist select what he considers a hardy variety. Remember that berries will develop only when male and female are planted close by.
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