Tip #1: Grow in the Coldest Room of Your Home
If you plan to grow Slender St. John's wort indoors, make sure to choose the coldest room of your home. This will usually be on the side of your house that doesn’t experience the harsh heat that the sun can produce in the middle of the day. At the same time, you’ll need to ensure the room does get a healthy amount of sunlight. While you’ll want to spare your plants from the brightest and hottest part of the day, zero sunlight can drastically reduce Slender St. John's wort ability to grow.
Tip #2: If Slender St. John's wort Doesn’t Flower Properly, It May Be Too Hot
The growing season for Slender St. John's wort, spring and early summer, can occasionally come with high temperatures. These fluctuations can negatively affect the growing stage of Slender St. John's wort, causing flowering buds to change into non-flowering buds. These buds will open partially, or in some cases not at all, causing Slender St. John's wort to lose some of its aesthetic quality. It's important to stay in the range of 65~75℉(18~25℃), for that reason, so your Slender St. John's wort can flower to its full potential.
Tip #3: Avoid Frost
While Slender St. John's wort can tolerate lower temperatures, as low as -5℉(-20℃), it will not do well if it encounters significant frost. If left out in the colder temperatures of late fall or winter, Slender St. John's wort will begin to show the signs of frost damage. To recognize the signs of frost damage, you’ll look for several key aesthetic changes. First, parts of Slender St. John's wort will begin to wilt. Then, those sections will start to become discolored, eventually turning brown or black as they die. Any parts of Slender St. John's wort that turn these colors cannot be saved, and will have to be pruned if you intend to keep the plant alive.