Fertilizing Lobelia

The flowering annual bedding variety of lobelia is considered a heavy feeder that can benefit from periodic feeding throughout the growing season. The soil should be amended with compost at the time of planting to give lobelia a nutrient boost from the start. As the plant grows in and establishes, mature lobelia plants benefit from a general liquid fertilizer to promote healthy growth. Perennial Cardinal Flower is native to North America and does not have high fertilizer needs like the annual cultivars but also benefits from occasional fertilizer.


How to Fertilize Lobelia

Lobelia benefits from fertilizing at the time of planting and then one or two times per month in the growing season. Lobelia prefers slightly acidic soil with a lower pH ranging from 5-6. You can test your soil through your local extension office for comprehensive pH and nutrient profiles. Fertilizer for lobelia should be applied around the root zone of the plant. Apply fertilizer after thoroughly watering your plants to prevent root burn. Follow the package direction of your fertilizer for the correct application rate and method. 

Best Time To Fertilize Lobelia

Adding compost at the time of planting is a good way to start your lobelia plant off with a boost. As the organic material breaks down, it will slowly release nutrients for the lobelia to absorb and promote root growth. Do not apply other fertilizers at the time of planting. The best time to start fertilizing is 3 to 4 weeks after planting as the plant matures. Lobelia plants can be fertilized once or twice a month throughout the growing season beginning in late spring. Fertilizer should not be applied during the peak heat of the day and should be applied in the morning or evening. 


Best Fertilizer For Lobelia

Compost is a natural slow-release fertilizer that helps to build the soil when planting. If you do not have compost, you can use a slow-release granular fertilizer in 5-10-10 or 5-10-5 NPK ratios at the time of planting. As the plant matures, you can use an all-purpose fertilizer with approximately a 12-4-8 ratio. Liquid fertilizers make a great choice for regular applications. Choose a fertilizer specifically made for flowering plants with a higher amount of phosphorous if you want to promote blooming. 

Lobelia Fertilizing Tips

  • Do not apply a fertilizer until lobelia has had time to settle
  • Apply fertilizer after watering to avoid root burn
  • Use an all-purpose fertilizer made for flowering plants
  • Fertilize once or twice a month until frost


-Always wear protective gloves and a face mask when handling chemical fertilizers.

-Closely follow all directions and storage guidelines that are on the fertilizer label.


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 Author Katie Endicott - Published 9-14-2022