There are over 250 species of aloe, but the most common is aloe barbadensis, also known as aloe vera. It is prized for its medicinal values: applying the juice of the aloe to your skin can help heal burns and scars. Aloe is native to Africa; in colder climates, it must be kept indoors throughout the winter. It's also important to avoid overwatering, as this can hurt more than it helps.
Diagnose Your Plant
To diagnose your aloe vera's ailment, inspect the colour and firmness of the leaves and the dryness of the soil. A small amount of oozing and stinking is normal, but more may indicate a serious problem.
When very healthy, young aloe vera leaves are full, firm and bright green, as pictured in the first photo. Older aloe plants or those kept outdoors can turn greyish as their skin thickens; this is normal, so long as the leaves stand stiffly upright. A dried-out aloe, as in the second picture, has very thin, droopy leaves with scar tissue. When an aloe plant turns yellow and mushy, it is being overwatered and is beginning to rot. When leaves turn black and droopy, they have frozen.
Aloe vera products can be purchased as health and beauty aids, but they are generally processed to remove some of the characteristics of pure aloe gel. The gel that oozes from a broken aloe leaf is usually very thick and sticky; it generally has a noticeable odour. If your aloe gel is extremely stinky and yellow, however, it can indicate an unhealthy plant. Yellowness and odour are signs of rot, usually due to overwatering. If your aloe is oozing gel from split leaves, those leaves have died due to overwatering or freezing.
Aloe plants have shallow roots that spread horizontally rather than vertically. They require very little water, and when overwatered can experience root rot. Aloe vera can be allowed to stay in its container until the roots fill the soil. When replanting, choose a container that's wider than it is deep, and fill with cactus mix, sandy soil or another mix that gets good drainage. Aloe can regrow its roots in certain cases.
Healing Your Aloe
Using the information above, determine whether your aloe vera is healthy, overwatered, frozen or dried out. If it has been overwatered, leave it in a warm and dry place with plenty of light, and do not water again until it has returned to health. If it has frozen, trim back the black leaves, working from the base of the plant toward the top; move it to a warm spot away from windows and drafts, with plenty of light, and don't water or move it until it returns to health.
General Aloe Care
Aloe plants should be kept warm year-round. They can survive droughts, but can not survive overwatering: water only when soil is completely dry, and be careful not to water unless leaves are firm and green. Never leave your aloe in a pot without drainage holes, and always use a well-draining soil (or mix sand into your potting soil). Bring aloe plants indoors at the first signs of winter, and keep away from cold windows or drafts. During winter months, water even less than in summer: your aloe will be dormant, and will not need water. Repot aloe vera in spring if necessary, and always give it plenty of light.