drought tolerant...or not

I've had enough of this gaillardia. It perks up for a day or two after I water it, but mostly this is how it looks: wilted. It's a plant that is widely sold as being drought tolerant. It blooms a flower or two or three at a time,  and the disappointing flowers last a few days, then what's left is the seed head. The seed head is more attractive than the flower, being a nice puffball that lasts. I haven't cut any of them off since this plant started blooming this year, but the puffball isn't enough to keep the plant, not when it sucks up as much water as impatiens, and flowering is not particularly attractive. I'm taking it all out today. But it is making me think about plants that are sold as drought tolerant.

Parthenium incanum (Mariola) - Type 1

In my mind, there are two types of plants that are considered drought tolerant. What I'll call Type 1 has thin thread-like roots which don't make much of a rootball. The stems are usually stiff and the leaves are small and also stiff. When thirsty, the leaves may wilt or wrinkle and shrink, or they may just turn grey (or greyer) and more brittle. The stems are woody or semiwoody so that the plant holds its form when thirsty. With too much water, they rot. The plants usually look terrible in the nursery pot, and show their stuff when planted in the ground. Attempting to transplant self-sown plants or well established plants usually fails unless plants are very small (less than a half-inch tall and wide, in my experience, since at that size, the roots can be more than a foot long). Plants typically grow slowly. In fact I don't notice that they have grown at all until I've ignored them for a while. This type is characterized by most native shrubs.  Mariola (Parthenium incanum), Prince's plume (Stanleya), yucca, native penstemon, and eriogonum are typical plants. I'll categorize Mediterranean plants such as lavender as Type 1 although they make a root ball but have threadlike roots. Since they do wilt, and look good in pots, maybe they are Type 1b or Type 1M. 

Stachys lanata 'Silver Carpet' - Type 2

The other type of plant that is sold as drought tolerant has a thick, dense root system, and frequently fleshy roots. The roots make a dense root ball in a pot. The leaves and stems are usually succulent as well, and when thirsty, the whole plant collapses or droops. If you keep the soil moist, they just grow faster/lusher and never rot. They recover well from being dry, seeming to make a miraculous recovery (which may be why they are considered drought tolerant). This type of plant looks great in a nursery pot. It is easy to divide and  transplant. They usually grow quite quickly, even the first year after planting, and can be very satisfying to grow because of this. Gaillardia is this type of plant, as is Stachys lanata (lamb's ears), Echinacea, daylilies (Hemerocallis). I don't consider them drought tolerant at all. It may also be a matter of cultivar, for I find that that the species Stachys lanata is fairly drought tolerant (particularly if given shade), but that the cultivars such as 'Silver Carpet' or 'Helen Von Stein' are water requiring.

Lavandula x intermedia 'Grosso' - Type 1

The first type of drought tolerance is like a car that gets really good gas milage, and can go long distances despite a small tank. The second is like getting 8 mpg, but you consider it efficient because there are lots of gas stations and you have a lot of money or gas is cheap.

Of course there are plants that don't follow this grouping. Agastache has a root system that looks like Type 1, but acts more like Type 2. Artemesia versicolor has roots like Type 2 but acts more like Type 1. You might think that cacti are like cars with a big tank, but they are also extremely fuel efficient and have Type 1 root systems.

So I'm taking out the gaillardia that I just spent $35 on, and am reminded of this lesson. I'll spend my money on Type 1 plants.