Cacti typically grow in arid regions where the soil lacks essential nutrients. Although they are adapted to nutrient-poor environments, cacti do benefit from occasional fertilizing to encourage optimal, healthy growth. Frequency, fertilizer composition, and application are all important to consider when feeding a cactus.
Choosing a Cactus Fertilizer
Cacti have adapted to grow in habitats where nitrogen availability is low, so choose a fertilizer that has a low nitrogen content. It is still a necessary nutrient for growth and metabolic functions, but excessive nitrogen may cause the cactus to become thin and weak.
The NPK ratio of a fertilizer indicates the proportions of nitrogen (N), phosphorus (P), and potassium (K). Specialized cactus fertilizers typically have an NPK ratio with lower nitrogen (2-7-7) to support the plant’s growth adaptations. If using a general, balanced fertilizer (5-5-5), dilute to half or quarter strength to avoid problems with overfertilization.
Note: Specialized plant feeds tailor nutrients to particular requirements. For example, leafy houseplants benefit from high nitrogen (3-1-2), whereas flowering plants would benefit from higher potassium (1-2-2).
Types of Fertilizer
Fertilizers can be either organic or inorganic and are available in both liquid and solid forms.
- Liquid Fertilizers: Diluted in water and applied directly to the soil. They are easily applied as part of the watering schedule.
- Granular Fertilizers: Applied as a top dressing or incorporated into the soil before planting. They gradually release nutrients into the soil over time.
- Organic Fertilizers: Nutrients derived from plant or animal sources. Examples include bonemeal, seaweed, manure, and worm castings. Chemical composition may be inconsistent.
- Inorganic Fertilizers: Nutrients that come from synthetic sources. Inorganic fertilizers have a consistent chemical composition.
How to Fertilize a Cactus
Cacti are sensitive to overfertilizing. Feed sparingly and take care to reduce stress on the plant and its roots.
- Moisten soil: Water the cactus a day or two before fertilizing. Applying fertilizer to dry soil may cause root burn.
- Dilution: Follow the instructions to dilute the fertilizer appropriately. When using a balanced fertilizer, dilute to half or quarter strength. Specialized cactus fertilizers may also benefit from half-strength dilution. Consider that underfertilizing is generally better than overfertilizing for cacti and succulent species.
- Avoid wetting the foliage: Direct contact from fertilizer on the stems or foliage may cause burns or damage, especially if the cactus is in direct sunlight. Apply fertilizer directly to the soil.
- Rest period after repotting: Wait 6 to 8 weeks before feeding a cactus after repotting to allow the plant to settle.
Note: Some potting mixes contain added nutrients. Although this is less common for cactus soils, check whether the particular mix includes a slow-release fertilizer. Cacti planted in enriched soils will not need fertilizing for the first year after potting.
When is the Best Time to Fertilize a Cactus?
Fertilize during the active growing season. Monitor for signs of new growth as the season approaches—offsets, leaflets, new needles, and stems indicate that the plant has resumed active growth. Fertilize no more than three times during the growing season. For many cacti species, twice is sufficient.
Avoid fertilizing during dormancy or extreme heat. The active growing period for winter dormant species is from early spring to summer, whereas summer dormant species actively grow from early fall to winter. In particularly hot summers, some species may slow growth to conserve energy. Refrain from fertilizing until normal growth has resumed.
Troubleshooting for Feeding a Cactus
Cacti are not heavy feeders. Too much fertilizer can negatively affect the growth and health of the plant.
- Excessive or abnormal growth: Rapid, leggy growth that appears weak.
- Root burn: Signs include yellow or browning plant tissues, stunted growth, and wilting.
- Pests and Diseases: Weakened health can make the cactus susceptible to pest and disease outbreaks.
- Salt build-up: Excessive feeding can cause a build-up of salts in the soil, which are detrimental to the roots. Signs include a visible white crust on the soil surface, hardened soil, and stunted growth.
In instances of overfertilizing, flush the soil with plenty of water and allow excess to drain away. In severe cases, repot the cactus into fresh soil. Refrain from fertilizing until the following growing season.
Tip: Consider that it is best to be cautious when feeding a cactus. If unsure, dilute liquid fertilizers to quarter-strength and feed just once at the beginning of the growing season. Monitor cacti regularly for symptoms of nutritional deficiencies and gradually adjust the fertilizing schedule as necessary.
Signs of Nutrient Deficiencies in a Cactus
Changes in a cactus’ growth pattern, health, or overall vigor may indicate a nutritional deficiency.
- Yellow or discolored plant tissues
- Distorted growth
- Stunted growth
- Poor flowering
- Weakened or brittle stems
It is important to maintain proper watering, provide sufficient sunlight, and use well-draining soil to cultivate healthy cacti. Many symptoms of poor health can also be indicators of problems associated with inadequate care practices. Take care to consider all aspects of the growing conditions before diagnosing a potential nutrient deficiency.