The Basics of Sub-irrigated Planters

Plant fertilizers – This is a HUGE subject but here’s a basic tip.

There are many schools of thought out there on this subject and for those of us who have been growing plants in pots, there is not much of a “science” to it, we know what plant fertilizers we like, what works better, or quicker or whatever. But there is new stuff to be learned and when it comes to the sub-irrigated planter, we have to change up the flow a little bit.

Most of the large sub-irrigated planters, troughs, the manufactured kits, etc., most all suggest a “strip of plant fertilizer” be laid down in the top 3 or 4 inches of the soil, on one side or down the middle, as long as it’s as far away from where the plants will be as possible. The idea is, with the constant moist soil, the nutrients will leach downward and the plants will take up what they need. It is an excellent idea and using the right kind of plant fertilizer in that strip means a well-fed plant.

Remember, however, that a sub-irrigated planter is a “passive hydroponic system” and as such, nutrients can be supplied through the reservoir water.
Now, don’t get me wrong…the BIGGER plants in the BIGGER SIPS require more plant fertilizer, and as such, I would include the strip or at least, mix it into the soil. But, speaking of the smaller sub-irrigated planter, the pop bottle up to, but not including a 5 gallon bucket, where a “strip” of fertilizer would be impossible to place without getting it too close to the plant…these are the ones I use liquid or soluble plant fertilizer into the reservoir.

Most of the potting mixes sold today include a timed-release fertilizer of some sort and make it easy to “fill-pot-water” and be done with it for awhile. HOWEVER, and this is a BIG however…don’t rely solely on these bags of amended mixes to be the “be all-end all” to the nutrient question! As good as SOME OF THEM may be, they don’t last forever, most are 3 to 6 months feeding, and they may not provide everything the kind of plant YOU ARE GROWING needs. We all benefit from a variation in diet, so do the plants!

For those of us who mix our own soils, we have found tried and true formulas for “general purpose” planting, but we have also may have a container set aside mixed for african violets, or one special for cactus, and the “general purpose” gets amended with extra calcium for say, tomatoes. This is in “the mix”. But as plants grow along, they might and probably will need more, and how do we do that? Easy-peasy…goes in the water reservoir as a liquid.
The plant fertilizers made for hydroponics work well, if you feel like experimenting. They cost a bit more, are often very picky over water parameters, i.e., ph, tds etc., but work great as supplemental feeding right beside the old tried and true granular water soliables.

I like to include Miracle Gro with a 1/4 teaspoon of SuperThrive to the gallon for filling the reservoirs, its a great starter for just about everything and can kick-start an otherwise sluggish little plant into action.

In my opinion, the sub-irrigated planter just makes it super easy to fertilize as a standard gallon mix of whatever you use and like, just gets poured into the reservoir. I do a quarter strength of the label recommendations to a gallon and I’m on my way!