There are lots of reasons growing plants in pots is so popular: It enables space-challenged gardeners to tend to a range of flowers, vegetables, and even dwarf trees and shrubs. It allows people in cool-weather climates to grow tropicals outside in warmer months and bring them inside when it cools off. And it allows plant lovers to try out newer varieties before planting them in a garden. But many people get frustrated when caring for potted plants because they don't understand the particular requirements of growing in a space-restricted environment.
Fortunately, Gayla Trail, author of Grow Great Grub and Easy Growing, has tried out nearly everything in a container. She walked us through the dos and don'ts of caring for potted plants.
BHG: What's the No. 1 mistake people make when choosing a pot for a plant and caring for potted plants?
GT: Beginners, especially, make the mistake of not understanding a plant and how it grows, and the worst thing you can do is try to grow something in a container that's too small. Size is where people can make the biggest difference in a plant's health.
BHG: So just how big of a pot should you get?
GT: I always say go for the biggest pot you can afford. I'm a big advocate of reusing things that aren't pots and turning them into pots. If you have a big pot, you don't run the risk of underwatering or undernourishing the plant.
BHG: Is it safe to say that everything you buy at a garden store should work well when caring for potted plants?
GT: Actually, no. There are a lot of pots at garden centers that don't have drainage holes, and the next biggest issue besides pot size is drainage. People assume that all products at garden centers are made specifically for growing plants, but a lot of those containers were made for putting another pot inside of, or they are just decorative. So for long-term growing, they are not practical. Drainage holes are an absolute must.
BHG: So, you've picked out a big pot and it has drainage holes. What about soil?
GT: Soil is tricky. I recommend going for what is best in terms of weight and texture. My rule: If I go to the store and I pick up the bag and it feels really light -- almost like a bag of popcorn -- that isn't good. But if it feels too heavy, it has too much filler and will end up compacting. So try to get soil that is somewhere in between.
BHG: What about nutrition? When caring for potted plants, do you have to put them on a regular fertilizing schedule?
GT: Containers are obviously contained -- there's only so much available for water and nutrition. So if you use a big container that's not overstuffed with plants, there's room for each plant to get some of the nutrition they need out of the soil. Containers also leach out nutrition faster than plants that are in soil, so you do need to fertilize more often. You can use compost, which provides good general nutrition. I also use worm castings, which are airier; you can add that through the growing season as a side dressing or just put it around a plant on top of the soil and mix it in. Dried sea kelp meal is a favorite of mine because it is high in potassium, which is a good stress reliever, and container plants are often under some amount of stress. Even leftover tea leaves work. I like to get as much fertilizer as I can by using things that I don't have to buy!
BHG: When you have your soil, your pot, and your fertilizer, how do you properly pot the plant in the container?
GT: You have to leave a 1- to 2-inch lip between the top of the soil and the top of the container. Especially when you water the container, if you don't have enough of a lip, the water will run off immediately, and only the top layer of the soil will get moist.
BHG: You bring up a good point: watering. Whether your plant is inside or outside, providing the right water is an essential step in caring for your potted plant, right?
GT: People are always looking for a formula, but the thing with watering is that formulas don't work. Especially if your plant is outside, you have to change how often and how much you water depending on the season and the stage the plant is in. So it becomes intuitive and depends a lot on you feeling the soil and understanding the plant.
Containers definitely affect it. A too-small container may mean the roots take over, and there's no room left for soil to absorb water. So a bigger container will have more soil to soak up water and hold it. Container material affects it too. For example, terra-cotta will dry out much faster. A rainy spring for an outdoor plant means less watering. In really wet seasons, I'll remove the tray underneath, but in a drier season or location, I'll leave the tray. The bottom line is, if your plant is showing distress -- wilting, for example -- you're watering too much. If it's shriveled, you've gone too long between watering.
BHG: You've mentioned plant and root size a lot, but for root size in particular, that's a hard thing to judge, right?
GT: Unless you have experience with a plant, when you're caring for a potted plant you don't realize how it will grow and change. When you go to the nursery in the spring and you're looking at the transplants, they're all kind of the same size. But a big variation that people never consider is the difference in root size. That comes with experience. I've done a lot of container gardening, and it makes you more conscious of size of roots, but really the only time you notice it is when you go to transplant the plant. A rule of thumb is a tall plant will usually have a much deeper root system, while a plant that crawls along the ground will have a shallower root system.
BHG: Won't plants adapt to the size of container, though?
GT: There are so many times that people are misled to think they can grow anything, especially herbs, indoors on a windowsill. So many people say to me that they can't garden, that they kill plants, that they've tried kits. Some plants don't do well in a window or a pot, or do well only for a very short time. Without understanding and managing expectations, it can be really misleading to beginners. Some things you can grow in the short-term in a pot, but you need to know what your plant needs before you decide short-term or long-term.
That said, some plants will adapt to cramped quarters well, including thyme; oregano; leafy greens such as cress, mizuna, and other mustard greens; chives; succulents (especially hens-and-chicks); rosemary (try a dwarf variety called 'Blue Boy'); and geraniums, to name a few.