December "In The Grow" - Indiana Yard and Garden - Purdue Consumer Horticulture

December “In The Grow”

Q: I have several hills of rhubarb. For the past three years, the rhubarb has had skinny stalks despite fertilizer, etc. Knowing this probably means I need to divide and re-plant the roots, I need to know when is the best time to do this.

Also, I have red seedless grapes that are young and have only been harvested for two years. The grapes are sweet, but extremely small. How does one produce larger fruit? — Audrey Gilland, Fort Wayne, Ind.

A: Divide rhubarb in early spring before the new growth begins or in the fall. Fall division necessitates a layer of protective mulch.

Some grape cultivars just produce smaller grapes than others. However, grape size also can be affected by poor fertility, insufficient light, drought, overgrown plants or heavy fruit set. For detailed information on pruning, climate, cultivars and more, ask your Extension educator for “Growing Grapes in Indiana,” (HO-45).

Q: I have several hydrangea bushes that barely bloom. In fact, only two of six have bloomed (two blooms on one bush, one on the other). I have tried everything: rose food, mire acid, plenty of water, etc. Please let me know what I can do to encourage them to bloom.

Also, I have a mockorange bush that is 3 years old and has never bloomed. What can I do? — Lynn Beauchamp, Plymouth, Ind.

Q: I have a hydrangea plant about 5 years old. When we moved four years ago, I brought it with me. It hasn’t bloomed since. I fed it, fertilized it, used epsom salts, and I also watered it often. It has morning shade and afternoon sun; it’s a nice big bush but has no blooms. I know it blooms because it had blooms on it when I bought it. What can I do to make it bloom? — Vivian Smith, Cromwell, Ind.

A: Hydrangeas may be in bloom when you purchase them, they may have bloomed in a warmer climate, and they may produce one or two flowers each year, but generally the bigleaf hydrangea (Hydrangea macrophylla) won’t produce its big blue or pink globes of flowers in our area. Buds are produced on the previous year’s growth, which is a problem for a plant not reliably hardy beyond Zone 7. The roots overwinter each year, but the tops are killed back to the ground, or at the very least, the flower buds are damaged.

There are plenty of beautiful hydrangeas for Indiana. Try Hydrangea arborescens ‘Annabelle,’ H. paniculata ‘Grandiflora’ and ‘Tardiva.’ They all produce white flower clusters that are pretty fresh or dried.

The mockorange (Philadelphus coronarius) has several cultivars that are much more floriferous than the species. It is usually a light bloomer, but it should begin to produce those blooms soon now that it has settled into its new site. Mockoranges need full sun or light shade and should be pruned after flowering by removing old wood or cutting the plant back to the ground. Be careful not to overfertilize with nitrogen, which will encourage vegetative growth instead of flowers.

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