By Erin Marissa Russell
If you’ve run into an article as you’re reading about plants that mentions nurse plants and were left scratching your head and wondering exactly what the phrase means, you’re not alone. Many gardeners among us have read this term (especially regarding cacti), but it’s commonly mentioned without being fully explained. That’s why we’ve taken the time to find out exactly what nurse plants do and what their role is in the plant world. Keep reading to learn all about it.
Put simply, a nurse plant is one that facilitates the growth of younger plants by creating an area underneath it for the seedlings to grow that is more favorable than its surroundings. While intuition may make you think that the area under another plant isn’t optimal for survival because seedlings wouldn’t get as much sunshine, you see nurse plants discussed most often in reference to those that grow in desert climates. As you can imagine, the shade is a major benefit of growing up underneath a nurse plant, but that isn’t the only way that a nurse plant improves the environment where the baby plants underneath it grow.
What those of us unfamiliar with more arid regions may not know about the desert is just how diverse it can be. While you’re likely to picture miles on miles of sand dunes with a tumbleweed or cactus here and there, in actuality the desert is made up of many individual microclimates. Little pockets of shade and moisture end up hosting many more plants than others, and one such pocket of more temperate conditions exists underneath nurse plants.
Mature shrubs such as cholla, creosote, or blackbush can end up shading and protecting many little seedlings of their same variety. Baby plants that grow in the microclimate a nurse plant creates enjoy a few different benefits that make their spot easier to live in than the desert around them.
For one thing, the shelter of the nurse plant provides some respite from the elements that can be so harsh in desert climates. The nurse plant’s branches shade the sun somewhat, while the baby plant will also get some protection from the wind. And because the seedling won’t need to emit as much water vapor to regulate its temperature (due to the shade the nurse plant provides), it saves water, too—and since it saves water, it’s less likely to experience drought stress.
Additionally, the area underneath a nurse plant is likely to be a little damper than its surroundings because the nurse plant’s leaves transpire a bit, dropping moisture to the ground below, and the protection from the elements also helps the soil retain some hydration. Water isn’t the only resource a larger nurse plant drops to the ground where it can benefit growing seedlings, either. When the nurse plant drops leaves or fruit, they add nitrogen and beneficial organic materials to the soil as they decompose, providing the baby plants with the nutrients they need to thrive.
There’s also a less obvious benefit that makes a huge difference in survival. Because many desert plants are thorny or spiky, when a baby plant grows underneath a nurse plant, an animal like a lizard or rabbit would need to brave those spikes to eat the seedlings. Plants underneath a larger nurse plant are less likely to be stepped on by wildlife as well.
Another term for the nurse plant relationship is “ecological facilitation,” which downplays the personification and intent that the term “nurse plant” connotes. After all, seedlings end up growing under nurse plants more frequently because the conditions there are more conducive to their survival, not because the plants enjoy caring for young ones or do so on purpose.
These relationships aren’t entirely a win-win, however. Seedlings that grow up underneath a nurse plant do become dependent on that plant for their survival, and they grow at a slower rate than young plants that strike out on their own. This is probably because the young plants are sharing resources with the more mature nurse specimens, so they slow down their growth to adjust to the lower rate at which those resources are available.
And sometimes, as growing root systems expand and begin to vie for the limited resources of the desert, one generation of plants may have to give way to another in order for any of the plants to survive. That’s why you will sometimes see maturing plants growing in the shadow of the dead husk of a larger, more established plant. The dead plant still offers them with some protection and will eventually decompose just like the leaves and fruit it has dropped and become part of the soil, feeding the young plants in death just as it did in life.