Nutrients

Nutrients are a requirement for all life, including plants. While these cacti can survive for a good while with just soil, light, and water, eventually health issues will show up. It may take a season or longer to see impacts of nutrient deficiency or imbalance. pH of the soil and nutrient feed is also related, as the pH affects each nutrient's availability to the roots.

Pick up some Masterblend 3 part formula (Tomato & Vegetable/Epsom Salts/Calcium Nitrate), or for a more costly and slightly less optimal ratio single part, General Hydroponics Maxigro or Megacrop. Mix at the label rate and feed somewhere between every other watering to 4 out of 5 waterings when daily highs are in the 68-86F range, with the non feed waterings being a flush using pure water or non nutrient products such as Recharge, liquid kelp products, etc. To prevent salt buildup, always flush and fertilize to at least 15% runoff.

The most common expression of nutrients you will see on products is NPK. When you see three numbers on the front of a fertilizer product label in “20-20-20” format, these are the percentages of Nitrogen (N), Phosphorus (P), and Potassium (K). These are known as the Macronutrients. To find inclusions of other nutrients, you typically have to look on the back at the Guaranteed Analysis table. Aside from those big three, other required nutrients include Calcium (Ca), Magnesium (Mg), and a whole spectrum of micronutrients, which are essential but present in miniscule quantities.

Nitrogen is the primary driver of growth in plants. It is a critical building block of amino acids, proteins, and the chlorophyll required for photosynthesis. It allows cacti to grow tall, girthy, green, and healthy. In typical fertilizers there are three common types of nitrogen: nitrate nitrogen (like calcium nitrate, which is immediately available for root uptake), ammoniacal nitrogen (which binds to soil particles and provides a steadier release), and urea (an organic form that requires soil microbes to break it down before the plant can use it).

• ** Deficiency:** Without N, growth stalls and columns experience chlorosis, a yellowing of the tissue all over caused by a breakdown in chlorophyll production. A lack of chlorophyll means the plant has less energy to use for growth and defenses. It also increases susceptibility to sunburn.
• ** Excess:** Too much nitrogen results in internal cellular growth outpacing the growth of the outer skin, resulting in splitting, soft and spongey growth, and pathogen susceptibility.

Phosphorus is required for cell division, photosynthesis, and carbohydrate metabolism. It also plays a key role in root development, pupping, and flower production.

• ** Deficiency:** In a state of phosphorous deficiency, possible symptoms include root structural breakdown leading to heavy columns tipping, reduced or eliminated pupping and flowering, and even etiolation despite adequate light. Phosphorous deficiency has a clear indicator that cant be confused with other issues - when P is deficient, the column moves available P up the column to support the newer growth, and older growth lower on the column becomes less vibrant, dull, and eventually turns a red hue. This is a common sight in underfed seedlings.
• ** Excess:** Cacti do not need a lot of P. An excess nearly always manifests as a micronutrient lockout deficiency due to incompatibility. It will chemically bond with zinc and iron in the soil, rendering them unavailable to the roots. Deficiencies of each will cause yellowing between ribs and at the tip. It will also interfere with uptake of calcium and magnesium, and it can even burn fine root hairs, reducing the plants total water and nutrient uptake.

Potassium (K) is vital for water regulation, structural and cellular strength, and disease resistance. It regulates the opening and closing of stomata (pores) in the CAM process, which is critical for minimizing daytime water loss, transpiring out moisture at night, capturing carbon dioxide, driving the synthesis and movement through the plant of sugars, starches, enzymes and proteins. This allows hardening of cell walls, the outer protective skin of the plant, and its structural core.

• ** Deficiency:** When Potassium is deficient, the cacti will move available K to the growing tip. This leaves older growth susceptible to cellular collapse which looks like yellowing, mottling, progressing to sunken or straw colored or brown spots. The plant will face increased susceptibility to issues like Alternaria, heat, or cold stress. In advanced cases of deficiency the lower columns structural integrity fails, leading to the column bending, collapsing, or snapping under its own weight.
• ** Excess:** When there is too much potassium in the soil, it crowds out other similarly charged nutrients including calcium and magnesium, leading to structural and cellular integrity issues or metabolism issues respectively.

Roots absorb calcium and deposit into cell walls, where it stays locked forever, like bones. Plenty of calcium allows thick cell walls and skin, which promote strong column strength, resistance to fungus, pests, and physical damage. It also helps to grow long, thick, brightly colored spines.

• ** Deficiency:** The progression of Calcium deficiency includes increased susceptibility to humidity spots, pests, fungus, a structurally weakened column, yellowing, and eventually tip dieback and halting of new growth.
• ** Excess:** Since calcium competes with potassium and magnesium, if it is too high in ratio related to either of those the plant will experience a deficiency of them. Heavy calcium presence in soil can lead to alkaline pH, locking out Iron uptake and leading to Iron deficiency - manifested as a bright neon yellow tip while the rest of the cactus remains green.

Magnesium is the central atom in the chlorophyll molecule. It is essential for metabolism, energy production, and it also gives the cacti its deep green color. It allows the plant to handle high intensity light without stress. It also helps transport phosphorous through the plant tissue.

• ** Deficiency:** Since magnesium is mobile, symptoms will manifest at the base first and creep upward. Reduced ability to photosynthesize leads to less growth, and even etiolation despite light and nitrogen. Basal bleaching, where the lower column turns to a lighter shade of green, then yellow, finally a cream color, skin becomes papery thin, and woody, even corking.
• ** Excess:** Again, Magnesium directly competes with calcium and potassium. An excess of Mg results in the typical signs of Ca and/or K deficiencies. When too high in ratio with Ca it can also cause soil degradation, turning the potting mix into a cement-like, muddy mess that retains stagnant water and triggers root rot.

Including but not limited to Iron, copper, zinc, boron, manganese, Molybdenum, Silicon, Sulfur. These are still required for proper plant health but in parts per million quantities vs the above macronutrients whole percentages. A well balanced micronutrient profile will benefit chlorophyll production, plant growth hormone regulation promoting fat new growth and pups, deep, even coloration, and symmetrical growth.

• ** Deficiency:** Various micronutrient deficiencies lead to stalled chlorophyll production, spotted yellowing, bright yellow tips, stalled growth hormone production, irregular cellular division at the tip causing weird growth or even terminated tips.
• ** Excess:** Micronutrients in too high of ratio lead to macronutrient lockout, brown or black spots on lower columns, and column splitting.

The optimal elemental nutrient ratio expressed in N:P:K:Ca:Mg is 1 : 0.4 : 1.6 : 1 : 0.35. On fertilizer products sold in the US, P is expressed in terms of P²O⁵ and K is expressed as K²O, which can be verified by examining the label.

* P²O⁵ x 0.436 = P

* K²O x 0.83 = K

So for a US label product, the optimal N:P²O⁵:K²O:Ca:Mg ratio is 1 : 0.92 : 1.93 : 1 : 0.35. Micronutrients are also important. For a deep dive on where this ratio comes from, check out this forum thread: https://cactiguide.com/forum/viewtopic.php?t=47603

Masterblend 3 part is the one product on the market I have been able to find that most closely hits these ratios and at a good price too. The other two options mentioned above are slightly off on the ratios but close enough that they shouldn't cause any issues. Masterblend has the added benefit of buffering the feed solutions pH to a perfect 6.3 when mixed properly and allowed to rest for 3 to 12 hours before use. It should be prepared as follows: Dissolve 2 parts Tomato & Vegetable, 1 part epsom salts in the majority of the water. In a separate container, dissolve 2 parts calcium nitrate and then add to the rest. Do not let mixed fertilizers sit for more than a day as you may see algae or bacterial growth or you could have the components react and create a suspension, indicated by clouding, which would change the nutrient availability and pH.

If you are going to use synthetic fertilizers, you should understand how to test your feed solution and soil.

It's best practice to reduce feeding things that push growth when growth would naturally slow or stop - when dormancy is approaching. This means cutting out all growth hormones and reducing nitrogen in proportion when daily high temperatures are soon forecast to get too far outside of the ideal 68-86℉ growth window. Other nutrients, including calcium, magnesium, phosphorous, and potassium are still valuable to these plants right up until they stop drinking due to dormancy to keep their immune response up during those dormancy periods.

To encourage flowering, boost phosphorous and potassium in ratio right before and right after the plants dormancy.

I don't think that synthetic nutrients as discussed above pose any health risk whatsoever to people consuming crops treated with them or to the plants, if applied properly. Do you always purchase organic produce at the grocery store, and never eat out at that serve non organic produce? Synthetics offer more consistent and controllable nutrient levels and ratios with no real downsides. But if you are insistent on remaining organic, the best option is to use organic soil amendments which are added when creating your own soil recipe. A specific recommendation would be Espoma Citris Tone (Other brands have different, less optimal ratios).

There are a varied assortment of other very helpful things to water or feed your cacti. To learn more about them, check out the Beneficials page.