Try lower concentration of protein or precipitant or both at the same time. Usually it's easier to decrease the protein concentration (and don't forget do decrease concentration when u perform seeding! ) 

Good luck!

Have you tried slowing down the nucleation step? I mean try lower temperature or adding paraffin oil to the reservoir.. I hope you have tried microbatch under oil set up too..

you need to try a fine screen varying pH  and PEG concentration. Remember many amino acids have isoelectric points between pH 5 and 6 so you will change charges of some amino acids rapidly around pH 5.5.   In other words many amino acids may go neutral in charge causing protein to come closer together and making hydrogen bonds rather than salt bridges. Try varying PH between 4 and 6 and PEG between 20 and 30%.

Hi Malwina

If it is possible attach your drop (sphe) picture to get better solution.

1- Do seeding (streak-seeding)

2- Change the pH around 5.5 (i.e. pH: 4.5 to 6.5)

3- Try similar condition with different buffer in the same pH range like MES, Na Cacodylate

4- Try with different method like Microbatch  

You should fine screen the condition from the crystal screen. Start with the pH (5.0, 5.1....5.9, 6.0) and find the exact pH where your best spherulites grow. Also vary your PEG 3350 and protein concentration. If spherulites still persists, try a different PEG such as PEG 400, 1000, 4000, 6000 to see if that can make a difference. If still no luck, use your optimum conditions to try a crystallization grade detergent to see if the spherulites will form well shaped crystals. 

Generally, you need to make crystal growth slower. If you would use crystallization in gel medium, it could be achieved by utilizing gel with smaller pore size (see Fig.1 in https://www.researchgate.net/publication/256745399_Atomic_force_microscopy_of_growth_and_dissolution_of_calcium_oxalate_monohydrate_COM_crystals.) In seeding method, you can vary concentration of precipitants (harder way) or decrease droplet evaporation rate (easier way).

Article Atomic force microscopy of growth and dissolution of calcium...

In some cases small variations in pH can be useful. Add a little bit of NH4OH into the reservoir solution. Ammonium will evaporate and change the pH in the drop. After some time it will change back.