My indoor lemon tree

[RootLover1]

Hi! My dear indoor lemon tree planted from seed is 10+ years old. A year ago there was a reign of bugs (spraying with green soap solution was unsuccessful), so I cut off all leaves and stems, leaving only a small trunk. After suffering, the plant started to regrow. Now that the plant has started flourishing, I installed an LED light to aid photosynthesis and took a soil sample to the laboratory to see how I need to fertilize it. Some of the leaves dried partially, so I assume there is a nutrient imbalance. I did not get enough sample to measure pH, because roots are so abundant in the pot (about 15L or 4 gal) and I did not want to damage them. I have pinched off apical buds to get more bushiness.

I will probably get the lab results today and share them with you.

 

[RockyAldo]

It looks like it has made a strong comeback after its challenges. Browning may be due to nutrient imbalance or fungus.

 

[RootLover1]

Aluminium: 34 mg/kg
Boron: 1.42 mg/kg
Calcium: 7600 mg/kg
Copper: 6.1 mg/kg
Iron: 435 mg/kg
Potassium: 831 mg/kg
Magnesium: 625 mg/kg
Manganese: 29 mg/kg
Sodium: 153 mg/kg
Phosphorus: 734 mg/kg
Sulphur: 152 mg/kg
Zinc: 13.7 mg/kg

The numbers should be of those forms available to the plant (Mehlich III extraction). Apparently, the soil is very fertile, with low amounts of manganese and aluminium. Perhaps anyone knows how to interpret these numbers better?

 

[cpp gardener]

The numbers all look good, except that Phosphorus and Pottassium are a little high, but since it’s potting soil and not in the ground the values are not critically so. When you do fertilize, use something with 10-20 % Nitrogen and low in P and K.

 

[Meadowlark]

Apparently, the soil is very fertile, with low amounts of manganese and aluminium. Perhaps anyone knows how to interpret these numbers better?

Looking at your calcium levels and other minerals, I sure would want to know the ph of that soil. Lemon needs an optimal range of 5.8 to 6.5 for optimal nutrient uptake. High pH levels in the soil can risk nutrient deficiencies.

 

[RootLover1]

Fortunately, the lab had just enough soil left to measure pH. It is 6.17.

Apparently, about 12g of dry soil is sufficient to do both analyses.

 

[Meadowlark]

That's good to go. Any idea of how your soil calcium levels reached those heights...more than an order of magnitude above optimal levels?

 

[RootLover1]

Is it possible that peat-based (potting) soils are naturally high in Ca, and other nutrients have been added in abundance by regular fertilization? I have used different nutrient mixes, including a specialized citrus fertilizer and some plain NPK for flowers. Today I shall apply ammonium nitrate solution to get some nitrogen. Should I measure soil N levels?

 

[cpp gardener]

No, I don’t think peat-based soils are high in Ca, in fact exactly the opposite. Have you mixed in any native garden soil with the potting soil? That could be the source.
Ammonium nitrate is a very strong N source. Be careful how much you use. Testing N is a good idea, although it is so mobile in the soil that the content fluctuates very quickly with every watering.

 

[tyronee]

I also have an indoor lemon tree that I got from eflorist, and it’s been such a rewarding (and sometimes challenging) experience. It’s amazing how resilient they can be with the right care. Sounds like you’ve done everything right — even cutting it back to just the trunk was a brave move, but clearly it paid off. Installing an LED light was a smart call too; I noticed a big difference in mine once I added supplemental lighting, especially during the darker months. I’ve also been dealing with some minor leaf drying and suspected a nutrient issue, so I totally get your concern. That’s great you had a soil test done — even without the pH reading, it should give you a better idea on how to move forward with feeding. Mine responded really well to a gentle citrus-specific fertilizer.

 

[RootLover1]

Found a photo of how it looked like one month after total pruning. Is your tree fruiting?