You’ve read the instructions; I’ve used them frequently here in my posts. “Drought resistant once established.” Sounds good—we’re always trying to save water—but how should you water these plants to start with? And what does “established” mean?
There are a lot of misconceptions about xeric plants. Our landscaper (who was much better at dealing with hardscapes than with living plants) thought that our xeric shrubs and trees needed to be sopping wet for the first few years, until they were “established.” Dead, more likely. (I’m already having to replace some fernbushes that were growing in muck, and we lost the top half of our oak tree in the first few months.)
One of our new neighbors thought that xeric plants didn’t need much water even from the beginning. He stuck some shrubby cinquefoils (a popular xeric native shrub) into the ground, mulched with rocks, and then wondered why the leaves were turning brown. (He’s now watering them—I hope it isn’t too late.)
So how can you tell when a plant is established? How long does it take?
As with pretty much any horticultural question, the answer is, “It depends.” Seedlings can establish quickly. The annuals we planted a couple of months ago are now full sized and blooming. Some perennials also establish quickly. For example, we planted a lot of catmint last summer. The plants look fully mature, and their roots are happily growing into the surrounding soil (top photo).
Trees, on the other hand, may take several years. Plants have a built in system that keeps roots and top growth in balance. If too much top growth is pruned off (or breaks in a storm), the roots send out a hormone that stimulates foliage production. And if the roots are cut, as happens in transplanting, the leaves tell the plant to grow more roots. (This is why it’s a bad idea to prune the top growth when transplanting.)
Assuming the tree or shrub was planted correctly, you can assume that it’s established when top growth resumes. That means the roots and leaves are once again in balance. In this photo, two of the Boulder Raspberries have been in place for a year and are established. The one in back replaced a plant that died over the winter. It’s not yet established as it was only planted last month. You can see the difference in size; all of these were the same size when purchased.
Establishing a xeric plant isn’t easy. There’s a happy medium between death by desiccation and death by drowning. The ideal is to have just as much air as water in the soil. Roots need both. For an average plant (whatever that is), the ideal is 25% air, 25% water, 45% minerals, and 5% organic matter.
You may have to water every other day—or even more often—to start with, particularly in hot weather. Drying out even once can kill the plant. And if it doesn’t, it can be difficult to get a dry root ball wet again. The soil the plant was growing in may not match the soil in your yard, and water doesn’t like to travel across an interface. So even if the surrounding soil is wet, the root ball may stay dry. On the other hand, if the root ball is damp and the soil around it is dry, the roots won’t leave their comfort zone. Plus, too much water can turn a planting hole into a bathtub. Good drainage is imperative, but it’s best not to inundate the plant in the first place.
This is why, when planting, it’s important to ensure that the roots can make a smooth transition into the native soil. For shrubs and trees, some horticulture professors now recommend washing all the potting soil off the roots before planting! This is one way to make sure that there is nothing stopping the roots from growing. It’s also a way to correct any problems, such as circling roots, that may later kill the plant.
Later, once the roots have grown into the surrounding area, xeric plants can get by with less-than-average irrigation. Hopefully, their roots have spread widely, ready to soak up even a light drizzle. They’re no longer dependent on a tiny root ball. In other words, they’re established.