Something has infested my St. John's Wort plants, and I think it is scale but would like your input. The leaves are heavily invested (from the ground up) with a pin head size 'dot' that is orange/yellow in color and cannot be wiped off. . . on the underside of the leaf. The top of the leaves have brown dots where this thing has eaten from the under side. My plants were so healthy and it seems this has happened rapidly. What do you think it could be, and how should I treat it?
It might be scale, but it might also be aphids. Regardless, they are treated the same. We have had great success with using neem oil on these types of pests. This article will explain more: https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm
Is St. John's wort plant okay with saltwater area?
Yes, it is salt tolerant.
I have several Hidcote St. John's Wort bushes for about 5 years now. This year they are growing nicely, very big and bushy, but hardly any flowers. I have them cut back each year in early spring. Is there anything I can do to have them flower more? Thanks.
By pruning your shrub in Spring you are simply cutting off that years flower buds.Prune after flowering in (say) October, but don't leave it too late. Then the buds will develop for next year.
St John's Wart is hardy to zone 4. Grown in a pot, the plant would be more vulnerable to the cold winter temperatures.
The pot can be placed in a sheltered, but cold location, such as a shed or garage.
Is one required to dead head St. John's wort?
It is not necessary to dead head the plant.
Pruning can take place in early spring, just before new growth starts.
Have had St John's Wort for at least 20 years, but after the first couple of years it's blooms diminished. We have added Peat to the soil, with limited results. The foliage appears healthy. It is in a mostly sunny spot, and I don't believe I can move it, although I have transplanted small offshoots.
You may have excess nitrogen in the soil, which will inhibit flowering.
You an feed phosphorous, with Bone Meal.
When can I transplant St. Johns Wort? What time of year?
Established plants are best moved either in spring after all threat of frost has passed or during fall, prior to frost.