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Rose Season Isn’t Over Yet

Some varieties want winter pruning

If your roses have grown tall and have been in the ground for less than a year, pruning them back to within 18 inches of the ground will minimize wind whipping, which loosens the roots in the soil.
    Grafted roses also need pruning to avoid damage to the graft union. You can identify grafted roses by the enlarged stem near the ground where the hybrid rose was joined to rootstock. Prune those tall stems back to about 18 inches from the ground.

Aluminum vs Ammonium

Q    I read your Bay Gardener’s tip about feeding azaleas ammonium sulfate after the first frost. However, I picked up aluminum sulfate without noticing the difference and used it on my azaleas at 1/4 cup each.
    What is the difference between the two? Have I caused any damage? Should I still feed the azaleas with ammonium sulfate? If I can’t find ammonium sulfate, what should I use instead?
    –J. Svedberg via email

A    Aluminum does not contain any ammonium nitrogen. If the pH of your soil is already low, the addition of aluminum could damage the plants, especially if the organic content of the soil is low. I suggest having your soil tested soon. Do not apply ammonium sulfate until after you have had a soil test.

Ask Dr. Gouin your questions at [email protected]. All questions will appear in Bay Weekly. Please include your name and address.

    If the graft union splits, the top of the plant will die and the original rose will sprout from the root. The rootstock for most grafted roses is either Dr. Huey or Ragged Robin. Neither produces attractive flowers. They are used as rootstock because their roots do not generate sprouts easily and are quite tolerant to nematodes and a wide variety of soil conditions.
    Knockout roses are a rose of a different sort. Because Knockout roses are grown from rooted cuttings, they do not require pre-winter care once they become well established. Thus, if the top dies back from cold or is broken by wind or run over by vehicles, new sprouts identical to the original stem emerge from the roots.
    Commercially, Knockout roses are field-grown and pruned using a modified lawnmower mounted on large-diameter wheels. Wherever the stem is cut, a profusion of new growth is generated from the buds.
    Don’t bother pruning out stems that are infested with cane borers. Let that job wait until spring. Pruning them back at this time of year can result in some winter kill, especially if we experience severe cold.