Why Strawberries Grow Misshapen and How to Hand Pollinate Them

A misshapen berry means incomplete pollination

Every seed on the surface of a strawberry has to be pollinated before the flesh around it swells. Wherever pollination failed, that part does not fill, so you get berries that taper to a point or are flattened on one side. They taste thinner too, and stay sharp.

So the shape is not telling you about disease or feeding. It is telling you what happened while the flower was open. Trace the cause back to flowering time and what to do next becomes obvious.

When pollination goes wrong

All five come back to the same thing: pollen has to be dry, mobile and moved. If any of those is missing on the day, the berry records it.

1. Too cold Pollen sheds at roughly 59 to 77F (15 to 25C). Through cold mornings the pollen does not move and neither do the insects, which is why the earliest flowers so often give misshapen fruit.
2. Too hot Above 86F (30C) pollen viability drops. Small, misshapen berries late in the season are partly down to heat.
3. Rain and humidity Wet pollen does not move and insects do not visit. Under an overhang or on a balcony there is also less air movement, so poor pollination is more likely than out in the open.
4. No pollinating insects Bees do not get into a city balcony, a cloche or a tunnel. Covering stabilizes temperature and reduces disease, but pollination is the one thing you then have to do yourself.
5. A late frost Frost during flowering blackens the center of the flower and that flower will not fruit. Cover on cold nights only, and uncover in the morning.

How to hand pollinate

Do it mid morning on the day a flower opens, while pollen is being shed. Take a soft brush or a cotton bud and stroke the yellow center of the flower lightly, in a circle. Press hard and you bruise it, which deforms the fruit in a different way.

A strawberry flower has both male and female parts, so you do not need pollen from another plant. Moving between flowers with the same brush does improve the set. A flower stays receptive for about two days, so you do not have to do it every single day.

1. Pick your time Mid morning on a dry day, once the petals are fully open. On a wet or overcast day the pollen is damp and will not move, so leave it until the next day.
2. Circle the center Stroke twice around the yellow center, working from the outside in. Those are the parts that become the seeds on the surface of the berry.
3. Move from flower to flower Carry on to the next flower with the same brush. The more pollen the brush is carrying, the more evenly the berries set.
4. Open the covers If you are using a cloche or tunnel, open it during the day when it is mild. That lets insects in and lets the humidity out.

With no brush to hand, simply flicking the plant with a finger to shake it helps. Indoors or on a balcony, making it part of the morning round produces noticeably better shaped fruit.

Thin the flowers to even out the size

A truss opens about ten flowers in sequence, and the later ones give progressively smaller berries. Reducing each truss to four to six leaves you with larger, more even fruit.

Flowers that open in the autumn and winter after planting are a drain on a plant that is still small, so pinch them off. Building the plant up and putting everything into the spring trusses gives you more fruit in the end.

Take the small buds at the end of the truss. Pulling by hand rocks the plant and disturbs the roots, so cut the flower stalk with scissors.

When flowers do not set or fruit stays small

If flowers appear but never turn into fruit, pollination is the first suspect, but excess nitrogen does the same thing. Large, dark, leafy growth with small fruit means you should stop feeding and see what happens.

If no flowers appear at all, the problem was in flower bud formation the previous autumn. The usual reasons are planting too late, too much fertilizer in autumn, or a winter spent somewhere too warm to accumulate enough cold.

From flower to picking

It takes 30 to 45 days from pollination to a ripe berry, depending on temperature: longer in the cold of early spring, shorter as it warms. Check daily, and pick once the color has run right up to the calyx, because that is where the sweetness is.

Strawberries do not sweeten after picking, so picking early costs you flavor. On the other hand a berry left to go over is an entry point for gray mold, so when rain is forecast pick slightly early and eat them that day.

Berries picked in the cool of the morning keep better. Picked in the heat of the day they start to spoil the same day.