Getting a Coffee Plant to Flower and Fruit Indoors

What an indoor plant honestly yields

This is worth being clear about before you spend three years waiting. A coffee plant grown indoors in a pot can and does flower and set fruit, and it is a genuine pleasure when it happens. It will not give you coffee in any practical sense. A healthy indoor plant of five or six years might set thirty to a hundred cherries in a good year. Each cherry holds two beans, so a really good season is perhaps a hundred and fifty green beans, which after drying and roasting comes to something on the order of an ounce (25 to 30 g) of roasted coffee. That is two or three cups, once, from a whole year of the plant's effort.

A field-grown tree in Colombia produces roughly a pound of roasted coffee a year, and it does that with full-day tropical light, deep root run and a proper wet and dry season. None of those exist in a living room. So grow coffee for what it actually is indoors: a genuinely excellent foliage plant with glossy deep green leaves in neat opposite pairs and elegant horizontal branching, that happens to flower with a scent like jasmine and set startling red fruit as a bonus. Judged that way it is one of the better houseplants there is. Judged as a crop, it will disappoint anyone.

The conditions that bring flowers

Flowers come on the previous season's wood on the horizontal side branches, never on the main upright stem. So a plant must first be old enough and branched enough to have that wood. Beyond age, the two things that decide whether a mature plant flowers are light and a period of slightly cooler, drier rest.

Light is the limit for nearly everyone. A plant that grows perfectly well in a moderately bright corner has enough light for leaves and not enough for flower buds. Move it to the brightest position you have that still keeps the midday sun off it, and give it a summer standing outdoors in shade, and you have done more for flowering than any fertilizer will.

Do not let a plant that is being prepared for flowering dry out completely during the cool rest. It wants less water, not none. A hard drought at that point drops the developing buds outright.

The cool dry rest that triggers it

In the wild, coffee flowers a week or two after the first rains break a dry season. Indoors you can imitate that, and doing so is what turns an occasional flowerer into a reliable one.

1. Give it a cooler spell For six to eight weeks in the dark part of the year, keep the plant at 59 to 64F (15 to 18C). A cooler bright room or an unheated but frost-free porch works. Never let it go below 55F (13C), which browns the leaves.
2. Water less during that spell Stretch the interval so the top two inches dry between waterings, rather than the usual one inch. Stop feeding entirely.
3. End it with warmth and a good soak When you want flowering, move it back into warmth and water it thoroughly. That combination is the signal. Buds usually appear at the leaf joints along the side branches within two to four weeks.
4. Keep the humidity up once buds show Bud drop from dry air is the commonest failure at this stage. If a humidifier is going to earn its keep at any point in the year, it is now.

From flower to ripe cherry

The flowers are small, white, waxy and clustered tightly along the branches, and they smell strongly of jasmine. They last two or three days and then collapse, which is normal and not a failure. Coffee is self-fertile, so a single plant sets fruit on its own without a second one, though indoors it helps to move a soft brush from cluster to cluster or simply to tap the branches once a day while they are open, since there is no wind or insect to do it.

What follows is slow. A pollinated flower takes eight to eleven months to ripen its fruit, which is why a plant carries green cherries for most of the year. They swell, stay hard and green for months, then turn yellow, orange and finally deep red over a few weeks. Pick them when they are fully red and give slightly to a squeeze. Green ones will not ripen once picked, and cherries left too long on the branch dry to a dark raisin, which is only a problem if you wanted the seed.

Record the week the flowers opened and the week the first cherry went red. Once you have that gap for your own plant, you know when to start looking the following year instead of checking hopefully every day for four months.

Why a mature plant refuses to flower

Almost always the answer is light, and almost always the owner has already ruled it out because the plant looks healthy. Healthy foliage is a much lower bar than flowering. Work through the list below in order, because the first two account for most cases.

1. Not enough light If the plant sits more than about six feet from a window, or in a north-facing room, it will never flower however well it grows. Move it to the brightest indirect position in the house and give it a shaded summer outside.
2. Too young or unbranched Flowers only come on side branches that formed the previous year. A single straight unbranched stem has nowhere to put them. Topping the plant to force side branching, done in spring, brings flowering forward by a year or more.
3. Never given a cool rest A plant kept at a steady 70F (21C) and watered evenly all year has no trigger. Give it the cool drier spell described above.
4. Too much nitrogen A general feed high in nitrogen used all year gives lush leaves and no buds. Switch to a feed higher in potassium from late summer onwards, and stop feeding entirely through the cool rest.
5. Over-potted A plant moved into a much larger pot spends two years filling it with roots and leaves before it thinks about flowering. Go up one size at a time.