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Saturday, September 22, 2018

Star Jasmine Needs Lots of Room to Grow and Correct Management

Q. I see some of the resorts with gorgeous masses of jasmine, and in many places it seems like they are pruned into low mounds for borders. How do I avoid the exposed leggy parts -- will the rootstock regenerate if I simply prune it all the way to the base?  What time of year to do that if it would work?
Star Jasmine picture sent to me. This star jasmine needs more room to grow!

A. The picture you sent helped a lot. Star Jasmine performs best probably as a vine rather than a groundcover but it can be used for both if given enough room to grow. The star jasmine in the picture is planted too close to the hardscape (concrete sidewalk, stone edging, etc) to be left there. This plant can be hedged but I would not recommend it. Hedging this plant with a hedge shears will make it always look "twiggy" or full of brown stems and brown leaf edges that you can see.
Yellowing star jasmine as a small shrub due to desert soil lack of organics, alkalinity and poor drainage
Star Jasmine is actually a fairly large plant that can grow 2 feet tall and 10 feet wide if left sprawling on the ground. This means that these plants should have about five with spacing between plants and planted about 5 feet from a hardscape. If I were pushed to fill in the area quickly I certainly would not put them any closer than 3 feet apart and 3 feet from a hardscape.
Star jasmine as a vine full of new growth because of  organics in the soil, fertilizer applications and watering
They don't look terribly good in our eastern Mojave Desert soils surrounded by rock mulch lying on the surface of the soil. They usually become yellow, scraggly in a few years because of soil and water drainage problems. This is a plant that prefers to grow in soil amended with compost at planting time and the soil covered in woodchip mulch.

Light pruning can be done anytime of the year when there is a problem with their growth invading some areas or becoming to dense. But the best time to prune them to optimize flowering is immediately after they finish flowering in late June or July. Pruning them then gives the plant a chance to rebuild itself for the next to flowering cycle which should begin in late spring.
Star jasmine will  become very woody if pruned continuously with a hedge shears
To do the type of pruning you are suggesting, basically a type of rejuvenation pruning or cutting it way back, should be done in late winter or early spring just before new growth begins. You can cut star Jasmine back very hard, so that 4 to 6 inches of old growth remains sticking out of the ground, and get it to regrow again into a plant full of new growth and flowers.

Pruning it as a vine is different. As a vine you want to retain its old growth and "balance" the remaining growth while encouraging new growth where the woody parts of the vine are appearing. Basically, you want the vine to be green and full of flowers from top to bottom. This requires a combination of different pruning techniques, fertilizing and watering.

Where the vine is dense and full of growth (usually near the top) thinning pruning cuts are made and in the sparse areas, heading cuts are done. Thinning cuts remove entire stems back to the woody stems. Heading cuts are made in the sparse areas (4 to 6 inches of growth remains) leaving a stub for lots of new growth.

Pruning cuts are followed with a fertilizer application (a rose or tomato fertilizer will work) and watered in.

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