Handling Newly Grafted Rhododendrons
Dr. Gick has kindly consented to conclude his notes on propagation begun in the October Bulletin of the A.R.S., Vol. 3. No. 1. -- Editor.
There has been some interest shown in an article on the propagation of rhododendrons by grafting, covering the care and handling of plants from the time they are ready to leave the grafting bin or cold frame. I can only give you the result of my experience in handling grafted plants and if any member can get any helpful ideas, I shall feel fully repaid.
As the facilities will be different in each case for members doing grafting and caring for the newly grafted plants, a general outline will of necessity have to be given, and then adapted to the member's individual facilities-such as a greenhouse, cold frames, bin in front of a sunny window in garage or basement, bell jars (1-gal. mayonnaise jar), etc. After the newly grafted plants are bedded down in the bin, there isn't much to he done except watch the temperature and ventilation for f weeks to 2 months. By that time there should he a definite callus plainly apparent. Probably the most difficult time with rhododendron grafts is the period immediately following the callusing when the time has come to lift the plants from the grafting bin. Upon inspection after six weeks, if the callus seems to be well formed, begin lifting the cover of the grafting bin. (And when grafting bin is mentioned, it means also the cold frame or frames if that is where the grafted plants are.) If calluses are not well formed, wait 2 additional weeks. Then lift the covers 2 or 3 inches 2 or 3 times a week until the cover is well up, watching the scions for wilting or flagging, and not allowing direct sunlight to enter.
Plants showing no scion wilt and those pushing new growth may be carefully lifted allowing all the peat that has become attached by the understock root to he retained. If there is available a bin or tray in a shaded part of your greenhouse or you have a spare section of the cold frame, bed your new plant down therein with a mixture of ⅔ peat and ⅓ loam. Otherwise pot your new plant down in a mixture of ⅓ peat, ⅓ loam and ⅓ compost (and by compost is meant well ratted cow manure or thoroughly composted garden waste). Keep well watered but no fertilizer at this time. Plunge pot in ground in a shade location. Have the pot 2 inches larger than the root ball in diameter, and put one inch of coarse gravel in bottom of pot for drainage. Where the grafted plant seems to he making slow progress-and some will be slow, or when there is wilt of the scion foliage, they should he left in the grafting bin and the cover lowered. In another couple weeks try lifting the cover by degrees again until no wilt occurs. Then lift them out as above outlined or set them upright in the grafting bin, as there is now room. Water well and hope for the best, but don't throw away as long as one leaf and one eye stays green. Most of the scions on the grafted plants will push new growth at the approximate time the parent hush naturally does, and of course one is glad to see that. A daily spraying during this period is very beneficial.
Bear in mind that these plants have been in a warm humid atmosphere for two months and the change to drier air should be gradual to prevent flagging. If however, in spite of the best care, the plant, especially the foliage of the scion, shows flagging or wilt, something different should be done than what is being done. It may be returned to the grafting bin if only 2 or 3 days has elapsed since its removal. Check the rubber grafting tie, make sure the root is not dry, change it to a cooler location, and if convenient, spray 2 or 3 times daily. These things failing, try setting an inverted 1-gal. mayonnaise glass jar jar over it and cover the jar with a cloth. Yes, some of them will die even for the experienced propagator, botanically no doubt there is a reason. 80% strike is considered pretty good; 90% strike is fancy.
If the grafting was done in February, you will very likely be taking the plants out of the bin during April to be potted or bedded down. By June 1-15 all plants should come out of the greenhouse or cold frames for planting. Prior to planting outdoors, with sharp pruning shears cut away the old top of the understock, making the cut about one inch from the callus, being careful not to disturb the callus. Also when moving the plants, check the grafting ties replacing any that need to be. Mention might be made here of the advisability of putting weatherproof tags with the name of the scion, either at the time of making the graft or at least when moving the plant out doors. Prepared aluminum tags are inexpensive, or get a sheet of thin aluminum and a spool of copper v, ire and-make them. Under the high shade of a tree or on the north side of a building or in a lath-house, prepare a bed about 10 inches deep of the mixture described above for potting.
Between June 1 and 15 take the new plants out of the greenhouse or cold frame and plant them in this mixture 18 to 21 inches apart each way. Plants should be set no lower than the original understock grew in the ground. Wet down thoroughly and put on a top mulch of 2 inches of sawdust, peat, or a mixture of half and half each. They can be left here until of sufficient size to enter the general planting scheme of the owner, given away or swapped.
During the summer the plants should of course have occasional watering,-a good soaking every week or ten days is the best. Frequent sprinkling, spraying or "washing their faces" is very beneficial especially during evenings of hot summer days. Watch for evidences of weevil, indicated by holes chewed in the edges of the foliage, and take proper spraying measures. Effective sprays with directions for using are available at all seed stores. In this connection, if thrip becomes prevalent in your greenhouse, grafting bin or cold frame, a light spraying or dusting of DDT preparation seems to be very effective. DDT preparations are also effective in eliminating pill bugs, and I cannot learn where it has been harmful to rhododendrons when used in moderate amounts. The following spring-February or March-one year from the date you made the graft and you are pridefully looking over the results of your handiwork, make sure that the last vestige of the rubber grafting strip is removed. Also check the callus, in case there was a hard freeze and it needs to be re-tied and a little grafting compound applied. If your plant is growing straight up in a single stalk, and you want it to branch, break out the center bud (it takes courage) after making sure it isn't a bloom bud. If suckers or sprouts start to grow on the understock anywhere below the graft, break or cut them off.
While soil preparation and fertilizing for rhododendrons do not come under the head of grafting and propagation, the next step in rhododendron culture will involve these two subjects, therefore a paragraph here may not be amiss. If your place is located on rich lake or river bottom loam, or your land is naturally "peaty," or your plant garden or woodland planting is underneath some oak trees where the leaves have been falling and molding for a hundred years, your problems are largely solved. But I expect 90% of us just have old "Willamette" type soil,-sticky when it's wet and bone hard when it's dry. This last mentioned type of soil needs some preparation and maintenance.
As outlined previously in this article, the best mixture is, I believe, ⅔ each of loam, peat moss and leaf mold. For the person living on one or two city lots, "loam" will have to be the dirt you excavated from the hole or bed. "Leaf mold" will have to be rotted cow-manure or thoroughly composted leaves, grass cuttings, garden waste, etc., or prepared dry manure available packaged in seed stores. (However, "leaf mold" being unobtainable, use half peat and half loam.) If time allows, prepare your mixture in advance, wetting it down thoroughly and mixing it frequently so that the hard lumps will blend. When moving a plant, dig the hole large enough to have from 4 to 6 inches of this mixture all around the root ball, being sure the plant is not set lower in the ground than it grew before. Make sure all peat is soaking wet when put in around a plant.
Did you ever dig up a shrub 2 or 3 years after planting and find the ground where you had put a "generous" amount of peat moss to be hard and solid? Well, the peat had disappeared,-disintegrated,-its usefulness lasting only while the plant was young or newly moved. I think this condition can be remedied by including 10% to 20% sawdust (leached if obtainable) in the bedding mixture. Rotted wood is also excellent, if obtainable. These materials will not break down as soon as peat, leaving the soil friable longer. All rhododendrons should have a top mulch 2 to 3 inches in depth,-a good mixture being ½ sawdust and ½ peat moss (or all sawdust if the cost is too high on the peat). This helps to hold moisture and keeps the fine feeder roots cool in summer, and is some protection against frost in winter. It gradually disintegrates, entering the ground as plant food, and should be replaced every year or two. As fertilizer, the best is probably fresh cow manure applied in the fall, being washed in during the winter and spring, the residue being summer mulch. But how many have friends with cows or a dairy? Next best is the homemade compost with some cotton seed meal added. And lastly if necessary, the so-called acid commercial fertilizers. These should be used sparingly, but I believe are useful if your soil is poor and other things are not obtainable. If it is necessary to use commercial fertilizer, apply it in small amounts 15 to 18 inches out from the stem, about every 6 weeks beginning in February and stopping the last of May. Before applying have a 3-inch mulch on the ground around the plants as this will absorb and hold the fertilizer making it more slowly and evenly available. In fact, where sawdust is used, the application of some nitrogen fertilizer is necessary. If plants are in a protected location sheltered against full natural rainfall, water abundantly artificially after each application.
Don't think you're cheating your nurseryman, because if you run true to form, you'll become a thrice better customer of his than before. This piece has had to deal with what is possibly a more monotonous aspect of grafting than the previous article.
However, it is work that has to be done and care that has to be taken: it is not long and tedious, but relaxing and restful for the short periods of time available to be given to it. An old horticultural saying goes "You have to love a plant to make it grow." and that surely applies to a freshly grafted rhododendron.