Southern Ag 4-18-38 Hydroponic Fertilizer
Water-soluble 4-18-38 hydroponic tomato fertilizer with key nutrients and trace elements for soilless systems. 25 lb bag.
Southern Ag 4-18-38 Hydroponic Fertilizer, also known as Hydroponic Tomato Special, is a concentrated, water-soluble dry fertilizer designed for hydroponic and soilless growing systems. With a high-potassium 4-18-38 nutrient profile and essential micronutrients, this formula is well-suited for tomato-focused hydroponic feeding programs and other vegetable-growing setups that require a dependable soluble fertilizer base. The official label identifies it as formulated for soilless culture and lists the net weight as 25 lbs. / 11.34 kg.
Use Southern Ag 4-18-38 as part of a complete nutrient mix with magnesium sulfate and calcium nitrate according to label directions. Its dry crystal form makes it a practical choice for growers who mix fresh nutrient solution for reservoirs, spray tanks, and transplant applications. The SDS lists the product’s recommended use as a water-soluble fertilizer and describes it as a solid crystal material.
Key Benefits
| Benefit |
Why It Matters |
| 4-18-38 NPK profile |
Provides nitrogen, available phosphoric acid, and soluble potash for hydroponic feeding programs. |
| High potassium content |
Useful for fruiting crop nutrition programs where potassium demand is important. |
| Micronutrient package |
Includes boron, copper, iron, manganese, molybdenum, and zinc. |
| Made for soilless culture |
Label states the fertilizer is formulated for plants grown in soilless systems. |
| 25 lb bulk size |
Suitable for frequent mixing, hydroponic gardens, greenhouse use, and serious growers. |
Guaranteed Analysis
| Nutrient |
Guaranteed Amount |
| Total Nitrogen (N) |
4.00% |
| Nitrate Nitrogen |
3.50% |
| Ammoniacal Nitrogen |
0.50% |
| Available Phosphoric Acid (P₂O₅) |
18.00% |
| Soluble Potash (K₂O) |
38.00% |
| Boron (B) |
0.20% |
| Copper (Cu) |
0.05% |
| Iron (Fe), chelated |
0.40% |
| Manganese (Mn), water soluble |
0.20% |
| Molybdenum (Mo) |
0.01% |
| Zinc (Zn), chelated |
0.05% |
| Chlorine |
Not more than 1.00% |
The guaranteed analysis above follows the official Southern Ag label. Nutrient sources listed on the label include potassium nitrate, potassium phosphate, potassium sulfate, ammonium phosphate, boric acid, copper sulfate, ferric DTPA, manganese sulfate, sodium molybdate, and zinc EDTA.
Label Mixing Snapshot
| Application |
Label Mixing Direction |
| Spray tank / transplant solution |
Mix 8 oz. / 227 g of Southern Ag 4-18-38 with 5 oz. / 142 g magnesium sulfate in 100 gallons of water. Once dissolved, add 6–8 oz. / 170–227 g calcium nitrate and dissolve completely. |
| Application interval |
Apply every 1–2 weeks. |
| Seedlings |
Use half rate during early seedling growth until plants are well established. |
Always follow the product label, adjust for your crop, water quality, and growing system, and avoid combining with Bordeaux, lime, or highly alkaline materials unless compatibility has been tested.
Product Specifications
| Specification |
Details |
| Brand |
Southern Ag |
| Product Name |
4-18-38 Hydroponic Fertilizer / Hydroponic Tomato Special |
| Formula |
4-18-38 |
| Product Type |
Water-soluble fertilizer |
| Form |
Dry crystals |
| Net Weight |
25 lbs. / 11.34 kg |
| Best For |
Hydroponic and soilless growing systems |
| Use With |
Magnesium sulfate and calcium nitrate, per label directions |
| Storage |
Store in a cool, dry area away from heat and incompatible materials. |
Storage and handling guidance is based on the SDS, which also recommends avoiding dust formation and avoiding contact with skin, eyes, and clothing during handling.
