Members of the Myrtaceae family, Eucalyptus are native mostly to Australia and Tasmania, where up to 800 species grow. Part of a closely related group of genera that includes Angophora and Corymbia, (known jointly as eucalypts) they range from shrubs to tall trees, including the world's tallest known broad leaf tree, Eucalyptus regnans. They grow in a wide variety of habitats and fast growth has made them valuable to the timber industry in some parts of the world. The common name, gum tree, comes from the sticky exudate of some species.
The immature, round, gray-green leaves found on most Eucalyptus houseplants are substantially different from the plant's typical mature leaf form and make an appealing display. But, Eucalyptus is a challenging houseplant. It demands plentiful sunlight and many varieties need to experience sharply cooler temperatures in the winter during their non-active growth period to maintain good health. Most importantly, this delicate young houseplant will swiftly become a large tree. Eucalyptus gunnii (cedar gum) is a popular plant and suitable to grow indoors temporarily, but you should be aware that your plant will probably outgrow your home and you may need to relocate or discard it eventually. Other dwarf cultivars and species can grow indoors for as briefly as a year and up to about five years.
Offering this plant enough light is one of the biggest challenges to its care. Strong direct light is crucial to maintaining a healthy plant with good leaf color. Full sunlight (at least 6 hours per day), from a southern exposure is best. This is not a good plant to try to grow in a low-light situation or without the right light direction; it will deteriorate quickly.
Take care not to under- or over-water. Water thoroughly, until water comes out of the bottom drain hole. Then let the soil nearly dry out before you water again. If it is hard to judge soil moisture, a water meter stuck down into the soil may help you get a good care routine established. In winter, the plant needs a period of less water.
The right planting container is important. If the container doesn't have a drain hole, or if the saucer under the plant isn't emptied after watering, the root system will stay too wet and the plant will decline rapidly.
Typical household levels of humidity are fine for this plant and no additional misting is needed.
Normal home temperatures in the 65 to 75ºF. range are ideal. Protect this plant from challenging micro-climates by keeping it away from heat and air conditioning vents and drafty doors and windows. It is sensitive to rapid temperature changes.
In winter, temperatures should be lowered to around 45 to 50ºF, from November through February, for many types of Eucalyptus sold as houseplants, including Eucalyptus gunnii.
Your Eucalyptus is a fast-growing tree and will use up its space in a container quickly. It will need to be re-potted every spring and some faster growing varieties may need re-potting twice a year. Move the plant to a container with a drain hole, one or two sizes larger than the last one and use equal parts of an organic potting soil, perlite or sharp sand for drainage, and peat moss. Some types of Eucalyptus need mildly acidic soil. Make sure that you get the entire root structure covered with potting mixture.
Many Eucalyptus problems develop when keeping the plant in a decorative container without a drain hole. You can insert a plastic pot with a drain hole inside of a decorative, non-draining container as long as you remove the interior pot when you water and allow the soil to drain completely before replacing your Eucalyptus in the decorative container.
Feed your plant once a month, in spring to fall, with an organic houseplant food.
In the winter, hardy Eucalyptus like E. gunnii will need a rest period with very little water, no food and lower temperature, about 45 - 50 ºF. This non-growth period during lower light conditions allows the plant to gather its strength for the next growing season and it will lose its vigor without the rest.
Eucalyptus is propagated by seed. Plant seeds in the spring in a seed-starting potting medium and keep in bright, indirect light, at 70 to 75ºF, in a covered propagation case. Bottom water for uniformly damp but not wet soil.. Once true leaves are present, individual plants can be potted on into small pots, in the same soil mixture used for mature plants (see 'Re-Potting"). Begin to water as a mature plant and be prepared to re-pot once the roots fill the container.
Some Eucalyptus plants arrive as gifts in the mail. Your plant will be stressed by its journey to you in a box. It will have had no light or water for a period of time and it may have been exposed to high heat or chill (or both). It will take a period of time to become acclimated to its new environment and to recover from the journey.
Keep it as stable as possible, give it the best possible care and don't make too many changes. Hopefully, with some patience and gentle care, the plant will begin to look more vigorous and you will begin to see new growth. Expect the plant to take several weeks to recover and for the improvements to be gradual.
If at all possible, buy your eucalyptus from a nursery or plant store and bring it home yourself to spare it (and yourself) this inauspicious start.
Leaf curl is a sign of stress. Your plant is letting you know that something is wrong with its growing environment. Consider these possibilities if your plant has dry and curling leaves:
Leaves become stiff and gray: If you are growing your eucalyptus as a houseplant, you are probably seeing only juvenile, rounded leaves on your plant. (There are mature leaf type as well but those rarely grow on plants that are small enough to keep as houseplants and some Eucalyptus keep these rounded leaves for most or all of their lives.) Even the immature leaves have distinct stages and the leaves may begin soft and green but become covered with a stiff, waxy, grey coating as they age.
The Houseplant Survival Guide by 
