If you’re growing citrus in Tucson, knowing exactly when to fertilize citrus trees in Tucson is the key to a healthy, productive tree. Getting the timing right helps your trees handle our intense heat and produce those sweet fruits we all love.
Our unique desert climate, with its hot summers and mild winters, creates a specific schedule for feeding your trees. This guide will walk you through the expert timing and methods to keep your oranges, lemons, and grapefruits thriving.
When to Fertilize Citrus Trees in Tucson
The golden rule for fertilizing citrus in Tucson is to feed during the active growing season and stop before the winter chill. You should never fertilize in the fall or winter, as this can promote tender new growth that will be damaged by frost.
The ideal feeding window runs from late February or early March through about August. Here’s a simple schedule to follow:
- First Application (Late February/Early March): This is your most important feeding. Apply fertilizer as the tree exits winter dormancy and flower buds begin to swell. This gives it energy for blooming and setting fruit.
- Subsequent Applications (May, July, August): Follow up with lighter feedings every 6-8 weeks through the summer. Your last application should be done no later than the end of August.
Why This Tucson-Specific Schedule Matters
Fertilizing on this schedule aligns with our natural weather patterns. The spring feed supports flowering. The summer feeds support the fruit as it enlarges and matures on the tree. Stopping in August allows the tree to slow its growth and harden off before any potential frost, which usually arrives in late November or December.
Signs Your Tree Needs Fertilizer
While sticking to a schedule is best, your tree might show signs it needs food. Look for pale green or yellowing leaves, especially if the veins remain green. Reduced flowering or very small fruit can also be a clue. Keep in mind that yellow leaves can also be caused by over-watering or poor drainage, so check your soil moisture first.
Choosing the Right Fertilizer for Desert Citrus
Not all fertilizers are created equal, especially for our alkaline desert soils. Citrus trees have particular needs.
Key Nutrients to Look For
- Nitrogen (N): This is the most critical nutrient for leafy growth and overall vigor. Look for a fertilizer where nitrogen is the first number in the N-P-K ratio.
- Micronutrients: Our mineral soils are often deficient in iron, zinc, and manganese. These are essential for preventing chlorosis (yellowing leaves). Choose a fertilizer that includes these, often labeled as “citrus fertilizer” or “with micronutrients.”
Recommended Fertilizer Types
A slow-release granular fertilizer formulated for citrus and trees is an excellent choice. It feeds the tree steadily over several months. Organic options like well-composted manure or a balanced organic blend also work very well and improve soil health over time.
Avoid using high-phosphorus fertilizers meant for flowers; citrus doesn’t need the extra phosphorous and it can lock up other nutrients in our soil.
How to Apply Fertilizer: A Step-by-Step Guide
Proper application ensures the tree’s roots can actually access the nutrients you’re providing.
- Water Deeply First: Always water the soil thoroughly a day before you fertilize. Applying fertilizer to dry soil can burn the roots.
- Find the Drip Line: Identify the “drip line” of the tree—this is the circle on the ground directly under the outermost reach of the branches. Most of the feeder roots are here, not right at the trunk.
- Spread Evenly: Broadcast the recommended amount of granular fertilizer evenly on the soil surface starting a foot from the trunk and going out to about a foot past the drip line.
- Water Deeply Again: After applying, water deeply again. This helps dissolve the fertilizer and carry it down to the root zone.
Special Note for Potted Citrus
Citrus in containers need more frequent but lighter feeding. Use a liquid or water-soluble fertilizer every 4-6 weeks during the same growing season (March-August). They leach nutrients faster with regular watering.
Essential Watering Practices Alongside Fertilizing
Fertilizer and water work hand-in-hand. Proper watering is critical, or the fertilizer won’t be effective.
- Deep and Infrequent: Water long enough so moisture penetrates 2-3 feet deep into the soil. This encourages deep roots.
- Adjust for Season: Watering frequency will change dramatically. You might water every 7-10 days in the spring/fall, but every 4-5 days during peak summer heat. Always check soil moisture a few inches down before watering.
- Use Mulch: Apply a 3-4 inch layer of organic mulch (like wood chips) around the tree, keeping it a few inches away from the trunk. Mulch conserves moisture, keeps roots cooler, and adds organic matter as it breaks down.
Common Mistakes to Avoid in Tucson
- Fertilizing Too Late: The biggest mistake is feeding in September or October. This can cuase a flush of new growth that gets killed by frost, wasting the tree’s energy.
- Over-Fertilizing: More is not better. It can burn roots, cause excessive leafy growth instead of fruit, and pollute groundwater. Always follow label rates.
- Ignoring Soil pH: Our water and soil are alkaline. High pH locks up iron, making it unavailable to the tree. If you see persistent yellow leaves, consider applying chelated iron as a supplement.
- Fertilizing a Newly Planted Tree: Wait until you see new growth after planting before you apply any fertilizer. Let the tree establish its roots first.
FAQ: Fertilizing Citrus in Tucson
Can I fertilize my citrus trees in October?
No. You should stop fertilizing by the end of August. Fertilizing in the fall promotes new growth that is vunerable to frost damage.
What is the best citrus fertilizer for Tucson?
Look for a balanced, slow-release granular fertilizer with micronutrients (iron, zinc, manganese). A formula with an N-P-K ratio like 13-7-7 or similar, labeled for citrus and trees, is ideal for our conditions.
How often should I fertilize a young citrus tree?
For the first three years, fertilize young trees lightly but more frequently—about every 6-8 weeks from March through August. This supports their rapid growth phase as they get established.
Why are my citrus leaves turning yellow even with fertilizer?
Yellow leaves (chlorosis) in Tucson are most often caused by iron deficiency due to alkaline soil, not a lack of fertilizer. Over-watering or poor drainage can also cause yellowing. Try applying chelated iron and ensure your watering schedule is correct.
Is it okay to fertilize when the tree is flowering?
Yes, your first spring application should coincide with the early flowering period. The nutrients support the blossoms and the small fruit that sets afterwards.
By following this Tucson-specific schedule and tips, you’ll give your citrus trees the best foundation for success. Consistent care with timely feeding and proper watering will reward you with lush growth and a bountiful harvest of homegrown citrus, perfect for our sunny desert gardens.