Like a goldfish in a bowl, a houseplant will only grow as large as the environment in which it is confined. So when your prized plants start to lose their vigor and color, the problem is usually due to growing pains below the surface.

Over time, two things happen to your indoor plants. One is that the soil, or potting medium, gets "tired" and becomes devoid of essential nutrients. The second is that a plant's roots will continue to grow, taking up more and more space in the pot. As this happens, the plant becomes "root-bound."

This combination of decomposing potting medium and cramped quarters inevitably leads to an unhealthy environment. The cure is usually quite simple: repotting the plant.

Repotting should be done twice a year, preferably in the late winter and early spring, and it's best to repot plants only when they are between flowering cycles.

Over time, all potting mixes decompose through the work of bacteria. As a decomposed particle gets smaller in size, it eventually gets washed out through the drainage holes in the pot. Smaller particles also settle, limiting the air space in the root environment. What happens is roots have more room to grow, but become root-bound in the small pot. With less potting medium around to hold water, the roots dry out and the plant begins to wilt.

But possibly the biggest sign that your plant needs repotting is how much room is left for new root growth. If the roots are growing out of the drainage holes or encircling the root ball -- or if you notice the appearance of brown, unhealthy ones at the bottom of the root mass -- then it's time to repot.

What's going on above ground is what's going on below ground. This means if the plant is getting bigger, then you can safely assume it's growing just as much below the surface. Pulling your plant out of the pot every so often is a good way to check on its needs.

How to Repot

To repot a plant, select a new container with a diameter at the top of the rim an inch to 2 inches wider than the original pot's diameter (a pot too large can lead to over watering).

If the pot has been used previously, use an anti-bacterial soap to kill harmful organisms. Clay pots need to be soaked overnight and then scrubbed to remove the white fertilizer salts around the insides.

Fill one-third of the new pot with premium potting soil. Premium products feature more ready-to-use organic material. Bargain products end up costing you much more since they contain little to no nutrients for the plant - and tend to "clump," making it difficult for roots to grow.

Next, gently shake off the old potting soil or mix from the root mass (while you're at it, check for any slugs). Carefully spread the roots out evenly. Make sure the crown of the roots is ½ to 1 inch below the top of the pot. This allows space for adding sufficient water, and it eliminates spills.

To finish the repotting process, fill in around the sides of the root ball with your potting medium. Gently compress the mix as you fill in. Then, water the plant thoroughly to ensure that all areas in the root zone have been moistened. When using a premium potting medium, the only maintenance you will need to worry about in the first month is watering.

It is important to know that repotting will not necessarily bring an unhealthy plant back to life. Plants with damaged roots, fertilizer build-up, diseases, or sunburned leaves may never return to a healthy state. Furthermore, repotting a sickly plant may cause more stress and possibly kill it. It is best to throw out visibly unhealthy plants and replace them with healthy ones.

Knowing When to Water

Now that you have your revitalized plant in a place that allows it to roam more freely, make sure you know when to water and when not to water.

One way to check is to press your fingertip into the soil. If your finger feels wet, you may be over watering the plant. If soil sticks to your fingertip, the plant is pleasantly satiated. And if none of the potting mix sticks to your finger, it's time to water.

Remember, your plants need care just as we all do. Keeping them well fed and watered with room for growth is a sure recipe for a healthy plant life.

Source: HEALTHY INDOOR PLANT: A GUIDE TO SUCCESSFUL INDOOR GARDENING