As a rule of horticulture, plant health is always determined by new growth. If a plant is growing, it is generally fine, but of course, there are exceptions. If a plant is growing but dropping as many leaves as it grows, this could be a sign that the plant is pot-bound or nutrient deficient. Plants might also drop old leaves as a sign of aging. When you’re assessing plant health, the best diagnosis starts with simple observations. Is it just one leaf yellowing and dropping, or is the whole plant showing signs of stress?
If a plant stops growing or is dropping perfectly healthy leaves, it’s usually a light issue. If you increase the light, you can spur new growth. If you increase light and nothing happens, try adding some fertilizer. Although some plants have a dormancy period, they usually will not drop their leaves unless they are deciduous, meaning that they drop their leaves and go dormant for a season. When you buy your plant, any good plant retailer will tell you if the plant goes dormant. Some common indoor plants that go deciduous include bulbs and some Dendrobium orchids. Keep in mind that most indoor foliage plants are evergreen.
Know the Green-ing
It helps to know what color your plant should be, in a fully healthy state. Although most plants are green, some naturally occur with other colors or variegation. If you bought your plant at a nursery or plant shop, whatever your plant looked like in the shop is what it should generally look like in your home. If your plant has lots of pigmentation, it will be harder to see if something is wrong with the plant, based on color alone. For example, many burgundy rubber trees are burgundy in color. This pigmentation may mask any leaf yellowing, but it’s not impossible to see if you look closely.
Unhealthy plants will die back more than they grow. They may grow in a deformed way or be discolored. Do not confuse blush (which is a reddish color associated with new growth for many plants) with discoloration. New growth is usually brighter than older growth, but will darken over time. Unhealthy plants will have an unhealthy look, growth that’s spindly, not much growth at all, and prone to insect infestations.
Healthy plants will grow unabashedly. Even if the growth is a little unruly, that’s still ok. Compare new growth to older growth on the plant — a healthy plant’s newer leaves should resemble the older leaves. If they are bigger, the plant is doing exceptionally well. And that means you are too!