Green thumbs might seem to have an innate knack for caring for plants, while black thumbs appear to be doomed with a Midas touch of death. But the only difference between green thumbs and black thumbs, really, is just familiarizing yourself with both your particular plants' specific needs and also some general plant-keeping guidelines.
These tips will help you troubleshoot the problems that inevitably arise no matter what kind of plant parent you are by nature:
Why are my plant's leaves turning yellow?
The most common reason for a plant's leaves turning yellow is moisture stress due to either under-watering or over-watering. If your soil feels dry and you haven't been watering that often, you can assume you may be under-watering. On the other hand, if the soil is wet to the touch and you have been watering frequently, over-watering is likely the problem.
To fix these problems, simply adjust your watering schedule. A watering meter can help you gauge how much moisture is in your plant's soil. Adjusting the plant's soil can also help; water-retaining soil can help keep a plant sufficiently moist, whereas well-draining soil prevents roots from becoming water-logged. Always make sure your pot drains well.
Consistent over-watering can lead to root rot, which is another moisture problem (bigger than moisture stress) that may also become apparent through yellowing leaves. To attempt to rescue a plant from root rot, check out these instructions.
Why are my plant's leaves turning brown?
Brown leaves are also typically a sign of poor watering habits. Specifically, shallow watering can lead to brown leaf tips. When you water, you want to water thoroughly, until water runs through the drainage hole (making sure your plant won't be sitting in water). A plant with leaves that are turning brown may also need additional humidity. Try lightly misting it, or place it on a tray filled with pebbles and a bit of water.
Another common cause of brown leaf tips is a buildup of salt in the soil from softened water or from over-fertilization. Watering with distilled water can help solve this issue.
How often should I water?
This really depends on the specific needs of your plant, but keep in mind that your home's atmosphere and the seasons can also affect how much you'll need to water. For instance, your home may be drier in the winter months when the heater is on. This will dry your plant's soil out more quickly, necessitating more frequent watering. Humidity-loving plants may also need a light misting when it's extra dry indoors.
In general, regular watering is the best, so setting a basic watering schedule of once a week is a good idea. Adjust accordingly for plants that need more or less water.
Do I really need to fertilize?
Many times, soil is fortified with all the nutrients a plant needs to survive. So you could go years without fertilizing and your plants will still live. However, if you want your plants to grow more quickly and really thrive, look into the type of fertilizer that is best for your plant. Usually, an all-purpose fertilizer is suitable, but you might find fertilizer specifically for indoor plants, trees, flowers, vegetables or evergreens. Make sure to fertilize only during the growing season, usually spring and summer. Over-fertilizing, just like over-watering, can cause problems for your plants.
How do I know if my plant has bugs?
Spider mites are too small for the naked eye to see, but you may notice your spider mite-infested plant begin to exhibit small brown or yellow spots on their leaves, or even spider-web type webbing. To address a spider mite problem, hose your plant down with a somewhat strong stream of water, which is usually enough to knock the spider mites off the plant.
Mealy bugs themselves are also hard to detect, but they make their presence known by leaving easily seen powdery webs on joints in your plant or on the underside of leaves. Mealy bugs may also produce a sticky residue on the plant's leaves that can spread to nearby objects. If you suspect mealy bugs, separate the plant from any nearby plants right away. Next, wipe down the leaves of the affected plant with a mixture of one part alcohol to three parts water with a bit of dish soap mixed in.
When should I re-pot my plant?
You should re-pot your plant when you want to give it the added boost of fresh soil or when it has outgrown its current pot, which will be exhibited by roots that grow through the drainage hole or that appear above the top of the soil.
Pistils Nursery has an excellent step-by-step of how to re-pot your plant. Take note that spring, which encourages a surge of new growth in most houseplants, is the best season for re-potting.