Last year I planted 25 gorgeous Russian sage in 1 1/2 gal pots. They were fabulous last year, but barely came back this year. We had a mild winter here in New Jersey, but even so, I know that is not an issue with that plant as I’ve grown it for years. This year I planted an additional 40 in the same hillside and they are doing phenomenally well. On last year’s plants, some have flowered a tiny bit, but none have come back to the size they were and most are so small, they look like they came from a 6-inch pot! Do you have any thoughts as to what I can do to improve the situation?
Also, although we haven’t had much rain, I am seeing what I’m assuming is mold on several of my plants: trumpet vine, roses, honeysuckle. The zucchini and cucumbers have been totally decimated so there is no fruit. White is covering the leaves and with the veggies, the leaves are crumbling and disintegrating.
There are a few possibilities for the poor showing of your Russian Sage (Perovskia atriplicifolia, now renamed Salvia yangii) plants. However, without knowing more details about the growing conditions, I may be offering you advice that does not help. If the pots you selected to grow your plants in were made of a thin material, there is a chance you did not provide them with enough protection from the winter temperatures. Planting them directly into the ground can help to avoid this, if it’s possible for you to do so in their location.
Depending on the amount of sun and moisture your plants are receiving, poor growth can result. Russian Sage plants like “a well-drained soil and need to
have a warm to hot, sunny position” in the garden. (The Cultivation of Hardy Perennials by Richard Bird published in London by B.T. Batsford Ltd in 1994) If the soil is too wet, root rot can occur.
If they are in the proper cultural environment (lots of sun and well-drained soil), then perhaps they are lacking nourishment. The Plant Care Manual by
Stefan Buczacki (published by Crown Publishers in New York in 1993), suggests feeding your plants with a general purpose fertilizer in mid-spring and in mid-summer.
As for your second question, I believe what you are describing is a case of powdery mildew. It is a fungus that shows itself in times of dry weather. The
main thing you will need to do is destroy all the foliage affected by the mildew. The mildew on infected foliage will spread to new foliage.
Powdery mildew thrives where plants are crowded and there isn’t enough air circulation, so give your plants space, a sunny site, and try watering in the
morning, and watering from beneath the plants (not over the leaves) so they are able to dry off during the course of the day.
Here is a link to the University of California-Davis, Integrated Pest Management
website. You can learn more about this fungus, including host plants, life cycle and management.
Colorado State University Cooperative Extension has some information about powdery mildew as well, including preventative measures and a recipe for making your own baking soda fungicide.