The Harmattan is a season in West Africa that occurs between the end of November and the middle of March. It is characterized by the dry and dusty northeasterly trade wind, of the same name, which blows from the Sahara over West Africa into the Gulf of Guinea. The name is related to the word haramata in the Twi language. The temperature is cold in most places, but can also be hot in certain places, depending on local circumstances.
This season differs from winter, because it is characterized by cold, dry, dust-laden wind, and also wide fluctuations in the ambient temperatures of the day and night. Temperatures can easily be as low as 9 °C (48 °F) all day, but sometimes in the afternoon the temperature can also soar to as high as 30 °C (86 °F), while the relative humidity drops under 5%.

The air is particularly dry and desiccating when the Harmattan blows over the region. 

The Harmattan brings desert-like weather conditions: it lowers the humidity, dissipates cloud cover, prevents rainfall formation and sometimes creates big clouds of dust which can result in dust storms or sandstorms

Source Wikipedia

Harmattan can be one of the most difficult seasons for gardeners in West Africa.
Cold dry morning and evenings, smouldering hot dry dust noons.
Humidity can get really low and therefore affect our humidity loving tropical plants.

Here are a few tips to help you through the harmattan season.

1. Mulching: Covering the soil of your potted plants with some organic mulch can protect your soil from losing moisture too quickly
2. Keep a watering schedule based on the needs of your plants. Your calendar apps can come in helpful for this.
3. Mist your plants. Mist your indoor and outdoor plants daily to help balance humidity. Plants with narrower leaves lose humidity faster than broad-leaved plants so pay attention to them.
   You can get a humidifier or a spritz bottle for this.
4. Harmattan comes with lots of dust, so remember to wipe the dust off your leaves. Dust can clog up the pores of the leaves, plants use their leaves for respiration. Avoid using oils or oil-based leaf shine products in harmattan when wiping your leaves. While your leaves will shine their pores will quickly get clogged with dust again. You can use just water to wipe of diluted milk.
   If you have a large garden and can’t possibly wipe every leaf use the spray or mist function on your hose to wash off the dust.
5. Feed your plants with organic fertilisers at the beginning of the harmattan season.
6. Consider moving some pot your potted plants around, cause often the direction of direct sunlight may change from where it was in rainy months

Listen to and love each plant based on their needs.

Happy plant parenting.