Ask Mr. Smarty Plants

Plumbago scandens (Doctorbush) is a tough heat loving native plant that is fairly drought tolerant. The more common plumbago that you will find commercially is not native to Texas. Plumbago auriculata / capensis is the blue Plumbago. Both of these can take the summer heat and sun. The problem that you are having is isolated to the plant that you have potted. Potted plants can't be treated the same as plants in the ground. In the Texas heat, it is a real challenge to keep plants happy and healthy in containers, but it can be done.

When you describe the pot as well drained, we are going to assume the soil has some kind of aggregate to facilitate easy drainage. If this is not the case and you are judging the drainage by how fast the water is running out of the pot, then what you might have, is a drain hole in the soil. Over time, soil can develop paths that the water will move through in a planter. Picture an underground river or tunnel, when this happens, water will simply run down the developed underground path and run right out the bottom of the pot. Leaving everything but the surface of the pot and the area around the hole, dry. An easy way to keep this from happening is to dunk the pot in a tub of water and submerge the whole container. Then wait for the bubbles of air coming from your pot to subside before removing the container from its bath. The bubbles are from the air pockets or tunnels, that have developed in your soil. The water soaking through all the soil will collapse these holes. If the pot is too big to dunk then place a tray under the pot and slowly run a hose on the container until the soil at the top of the pot is covered completely with water. Keep the hose going as though you are trying to drown the pot and keep the surface of the pot underwater until the bubbles stop. If you do this about once a month you will keep the spoil in the containers free from air holes and the watering you do, will be more efficient. This is a good practice to keep with potted plants in general, however we don't think that this is the root of your problem.

The most common problem with potted plants in the Texas heat is having the soil stay too hot for the plants comfort. Your plumbagos that are in the ground are happy with the care you are providing. The ground itself serves as an insulator from the heat. The type of material the container is made of, is a key clue to how your potted plant is responding. The best types of pots for a plant in the heat is a thick unglazed clay pot or a wood planter; both of these materials breath. They won't hold the water in the soil so long that you end up steaming the plant. If the pot is plastic, or resin, or even glazed, you can end up with containers that will literally steam your plants like a cooked vegetable. When this happens the plant will start to turn brown, then white. Once it is white, its toast.

Plants that are stressed out from over watering will look very much the same as plants that are stressed out from being under watered. If this is a big pot and you are watering every other day in 98 degree heat, combined with a container that doesn't breath, then this might be the problem and we suspect that it is. Plumbago loves the heat but it doesn't like it's leaves or flowers to get wet at all and it doesn't like to have its toes wet for too long. Even droplets of water on the leaves, left on too long in the hot sun can burn them, so be careful when watering and back off on the schedule. Dunk it first, to get out all of the air holes, then water about once a week. You can also place a handful of mulch on the top of the container to insulate it a bit. Pamper your plumbago with a watchful eye and see if these changes don't clear it up.