How to Grow Strawberries Indoors
Growing strawberries indoors can yield great results, but it has some challenges.
If you really like this aromatic and healthy fruit and have some indoor area to spare, give them a chance, they might surprise you.
Updated: April 15, 2020.
Before starting to grow strawberries indoors, there are few things to consider:
Growing Location, Light and Temperature
Indoor location for growing strawberries can be everywhere - ordinary windowsill, on flower shelf with other decorative plants (strawberries are both good tasting and very decorative plants), on the wall using some vertical growing system etc.
Strawberries grow best on room temperatures between 20 and 25°C (between 68 and 77°F), but they will tolerate both colder and warmer temperatures. After all, their vegetation period starts early in Spring and continues to the late Autumn. This of course highly depend on geographical location and somewhat on strawberry variety.
Strawberries will also tolerate some draft, but sudden drops of temperatures can harm the plant and lower the fruit yield.
Strawberries are plants that grow on a direct sunlight, even during summer. Strength of direct sunlight is between 32.000 - 130.000 lux, even 180.000 during summer, depending on location and season. Strawberries can grow in shade, but much better on direct sunlight. So, if you are not growing strawberries on a windowsill on southern window, consider having some sort of artificial lighting that can provide enough light for growing plants.
When berries are outside, there are no problems with pollination. However, indoor strawberries must be hand pollinated. This is not complicated and it doesn't require much time.
Strawberry flowers are ready for pollination when petals are fully opened, pistil (female part) is yellow-greenish and stamen (male parts) are brownish. We say '-ish' since this vary little bit from variety to variety, especially from berry to berry - various berries can be grown indoors, not only strawberries.
For hand pollination small, relatively soft, makeup brush is recommended - gently brush the pollen from stamen to the pistil and do this from flower to flower. Be sure to cover entire pistil, or you can end-up with partially pollinated strawberry. Also, after finishing with last strawberry flower, feel free to start all over once more - this way one is certain that there are no missed flowers and that whole pistils are pollinated.
Note: there are hand pollinators on the market, that operate using small batteries. Personally, I have never used one and therefore, I can't recommend any of them.
Pollination can be done on a daily basis - when strawberry flower is pollinated, white petals will soon start to die, leaving green sepal (green leaves surrounding the flower, below petals) around soon-to-be strawberry.
Strawberry Types and Varieties
Day neutral strawberries are recommended type for growing indoors, especially Alpine strawberries. Ever bearing varieties can be used, too, but they don't bear fruits all year long.
Note on Alpine strawberries: there are several names for this type of strawberries, but these strawberries look like wild strawberries, taste like wild ones, they grow no runners, and if conditions are met, they bear small and very aromatic fruits all year long.
Day neutral strawberries can bear fruit all year long, just keep temperatures during summer below 40°C (104°F) and during winter above 15°C (59°F), especially if you grow strawberries on windowsill.
Having 20-25 small Alpine strawberries doesn't require much space, provide enough flowers for almost daily pollination and bear fruits on a daily basis - their fruits are very small, but single Alpine strawberry fruit leaves enough flavor and fragrance in mouth that it is simply a shame to drink water after consuming it :)
Growing System and Watering
Depending on the strawberry size, a strawberry plant requires 0.5 to 2l (dm3) of soil. Alpine strawberries can be grown rather dense, but they also need some space. On average, if you provide 1-1.5l of growing soil per plant, strawberries are going to be happy.
Strawberries can be grown hydroponically and such systems doesn't require much maintenance, after they are set up. Also, such systems are usually vertical growing systems and they provide best yields per occupied area. But, setting them up can be time consuming and costly and hand pollination is a must. Such systems also include artificial lighting for plants in the form of LED lights or small fluorescent tubes and as such, they often doesn't require to be positioned near the window or glass doors. Turning lights on and off and water circulation is controlled using electronics. High-tech systems obviously cost some decent money :)
If you are interested in growing strawberries at home, start with vertical container having 4-6 positions per row, with height up to a meter (3 feet). Position such container near the glass door and use 2 (two) fluorescent tubes or equivalent LED grow lights for artificial lightning of the container that are turned away from the door/window. Tubes/LEDs should be positioned vertically, some 40cm (16 inches) away from the vertical container, some 60-90° away from each other. If possible, use light meter to check light strength on various positions and turn lights on and off automatically or manually. Automatic timers are rather cheap these days, so consider automatic turning on and off.
If you plan on growing strawberries on a windowsill, you can use rectangular containers or round pots. Rectangular containers provide more growing area per length of a windowsill, but round pots are easier to manipulate and rotate on regular basis.
I prefer growing more plants on area that I have, but round pots are much better in this case - all of this is IMHO, of course.
Growing Soil for Strawberries
Strawberries prefer slightly acidic soil with a pH level between 6.0 to 6.5. Also, pH level between 5.5 to 7.0 is acceptable, but ...
pH level of the soil can be tested using small test kits - take a small amount of your soil, mix it with chemicals provided and compare the color with chart provided with a kit.
Strawberries require balanced nutrient levels - nitrogen for leaves, potassium and phosphorous for flowering and bearing fruits. Not to mention many other required microelements ...
This is oversimplification, of course, but if you add, for example, too much nitrogen, you will get plants with plenty of large leaves, but only a few of flowers and fruits that are prone to diseases.
Growing soil should be enriched using compost, humus, aged (or dried - in the form of pellets) cow or horse manure and NPK fertilizers optimized for strawberries.
NPK fertilizers with gradual release of nutrients (up to a 4-6 months) are highly recommended in combination with organic fertilizers.
When growing strawberries on a small area, it is perhaps the best to buy sterile soil optimized for strawberries and NPK fertilizers with gradual release of nutrients.
Harvest - finally :) When growing strawberries at home, indoors, ripe strawberries can be picked up on a daily basis and consumed right away.
Strawberries taste the best when they get their characteristic red color - take your time and if needed, pick the fruit a day later, especially if you are testing a new variety.
Strawberry Pests and Diseases
Strawberries grown indoors are protected from mice and birds, but sometimes pets can be rather damaging - parrots and similar birds are often let outside of birdcages and if left unattended, they can make a mess not only by eating ripe fruits, but they can damage the plants and dig the soil out.
Insects and diseases can and should be treated with (preferably) organic agents.
Certified strawberry plants should be grown in soil treated with a methyl bromide-chloropicrin mixture or SMDC (Vapam) - this will greatly reduce the damage from viruses, nematodes, red stele and other insects and diseases.
However, in some cases, usage of fungicides is required. In that case, carefully read the instructions and whatever you do, do it outside.
After plants are treated, be sure to wait required period of time, before picking the strawberries for consumption.
Strawberries are easy to grow - they require some care and some time, but very soon, they will pay you back with rich and tasty crop. Don't hesitate to test various types and varieties, because you never know what is the perfect strawberry for you, until you find one ... Even then, some surprises are maybe just around the corner :)