Answer: I'm sorry about your plants!In my garden, tithonia has always been sturdy enough to support itself, so there may be several factors at work in this case. First of all, your garden may be unusually windy or in a spot where violent patterns occur. If this is the case, you may just need to stake the plants.
Next, make sure you are not over fertilizing the plants. Overfeeding can cause them to grow taller than normal and have overly large and lush foliage that acts like a sail in the wind. The combination can cause plants to topple in a wind that less succulent plants would be able to tolerate.
Finally, make sure you are not overwatering and as a result encouraging shallower than normal rooting. These plants are usually deep rooted, and they are known for thriving in sunny and relatively dry locations because they are so deep rooted. Deep roots also help to anchor the plants more securely. To water these, water very deeply and less often, say a deep soaking about once a week or so if it hasn't rained.
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