By Pathumwan
Nottinghamshire,
United Kingdom 
Hi, A couple of years ago I bought a lot of Alliums and put them in big pots and planters, the first year they were great big flower heads the second not as big, this year only as big as a dandelion head, could any one tell me what I am doing wrong, do I have to lift them each year and replant? or is there something else I am missing out.
12 May, 2019
Answers
Next year I would give then fresh soil and then give them some slow release fertilizer granules. if there is any foliage still green spray them with a foliar feed. They also benefit from the heat and dryness of the soil. so if they stay in the pot with other plants in the summer they may be too wet to mature for next year. Does this make sense?
12 May, 2019
After flowering this year give the green foliage plenty of shots of a weak liquid fetiliser in the water. After the foliage has died down allow to dry out then repot the bulbs in good, fresh compost.
12 May, 2019
Thank you all for your answers I will certainly try them next year, When is the best time to repot them?
13 May, 2019
i usually check mine after the foliage has gone and put them back in the old compost until late autumn then repot then.
13 May, 2019
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Have you replenished the soil in any way?
12 May, 2019