From our perspective as geraniums (Pelargonium spp.), our most critical requirement for a successful start in a new location is warm soil. Our roots are highly sensitive to cold and damp conditions. Planting us when the soil is still cool from winter significantly increases the risk of root rot, a condition where our delicate root systems fail to develop and instead decay. This stunts our growth before it even begins and can be fatal. We require soil temperatures to be consistently at or above 60°F (15°C) to actively grow and establish ourselves. This warmth signals to our biological systems that it is safe to expand our root network and seek out nutrients and water.
Our above-ground growth is equally vulnerable to cold. We are tender perennials, meaning we cannot survive a frost. Even a light frost will damage our succulent stems and leaves, causing them to blacken and wither. This not only sets us back severely but can also kill us outright. Therefore, the timing of planting must occur only after all danger of the last spring frost has completely passed. This date varies greatly by geographic region, so it is crucial for our caretakers to know their local frost-free date and monitor the forecast diligently. Our survival depends on this simple fact.
For the vast majority of climates, the optimal time to plant us is in the late spring. This period typically offers the perfect combination of warm soils and reliably mild air temperatures. Specifically, this translates to a time several weeks after the last average frost date. For many, this is around mid-to-late May. This timing allows us to use the entire growing season to establish a strong, extensive root system and develop robust foliage. A strong foundation in late spring directly translates to our ability to produce a profusion of blooms throughout the summer and well into the autumn.
Our start in life influences this timing. If we are purchased as young plants from a nursery, we have likely been raised in a climate-controlled greenhouse. We are accustomed to perfect conditions and are therefore quite tender. We must be "hardened off" before permanent planting. This process involves gradually acclimating us to outdoor conditions—wind, sun, and cooler nights—over 7-10 days. Only after this hardening-off period and when nighttime temperatures stay above 50°F (10°C) should we be planted. If we are started from seed indoors, we require an even longer lead time, needing to be sown 12-16 weeks before the intended outdoor planting date to be of a sufficient size.
In regions where winters are very mild and frosts are rare (USDA zones 9-11), an alternative and highly beneficial timeline exists: autumn planting. Being placed in the ground in early autumn allows us to establish our roots in the still-warm soil without the intense heat stress of summer. We can focus our energy on root development rather than supporting top growth and flowers. By the time the cooler winter arrives, we are already well-established. This gives us a tremendous head start for the following spring, often resulting in an earlier, larger, and more spectacular display of blooms compared to our spring-planted counterparts.
