Years ago, after getting a taste for gardening, I wanted to build my own planter.
Something portable (since I was renting). I also needed to keep my plants watered. So I designed my
very first sub-irrigated planter. I filled it with retail potting mix and it was up and running.
Fast forward 11 years. The planter's still functional. I still get awesome crops. I'll
top off the mix as needed, but it still has the original potting mix.
It's turned into this deep rich humus. A crucial key to success is fertilization.
Large, vigorous plants are gonna draw up lots of nutrients. So each season the soil needs
replenished. For years I've tested vegetables in these 3 SIPs. I kept track of my inputs.
I even began recording my harvests. From this wicking bed, last year I harvested over 44 pounds
of sweet peppers. And 110 pounds of watermelon. All pulled from 30 by 70 inches of soil.
Whether it's corn, tomatoes, zucchini, lettuce or cucumbers, these systems have performed well.
I'll share what I learned so you can maximize your yields!
To start, I wanna discuss fertilization in general. Some gardeners want to be as
"sustainable" as possible. Perhaps they won't use synthetic fertilizers. Only organic. Some
don't even want to buy any products. The idea is to take free organic products, compost them down
and cycle them into the garden. It's almost like a badge of honor to be completely self-reliant.
Homemade composting and vermi-composting with worms are like the gold standard for nutrient
replenishment. I couldn't agree more, in concept. I've harvested countless gallons of worm castings.
My compost tumbler still churns out lots of compost. But I apply it in other areas of
my garden. My conventional raised beds. My seed starting mixes. So I agree with these
approaches. I just don't use those inputs in my SIPs, wicking or 'self-watering' beds.
Years ago, I cautioned against bagged composts or manures, like you find at big box stores.
Why? These agricultural industry by-products can vary in quality and texture. In the ground or
raised beds they work fine. But many won't wick well in SIPs. This applies to top soil as well.
The ultra fine, silty particles get mucky when wet. Pore spaces plug up causing an anaerobic
environment. We don't want root rot to set in. Homemade composts might work. If you can make a
woody compost with a loose texture. I did a small test. Using peat moss,
vermiculite and homemade compost. The plant grew well. So this might be an option.
But compost can vary from batch to batch. And what about first-time gardeners who don't have
any quality compost? I want everyone to enjoy success, even if they're just starting out.
That's why I focus on testing organic fertilizers and even some time-release stuff.
These nutrients are readily available to most gardeners from day one. They're more
concentrated than bagged manures or composts, making them easy to work with. Quite importantly,
with a guaranteed analysis you can consistently determine how much to use in the bed.
All-purpose fertilizers can keep your SIPs running at peak performance without negatively
impacting aeration or wicking properties of the substrate. I've seen consistent results
even after a decade of use. So what have I been using? How can you apply nutrients in SIPs?
On my site, Albopepper.com, you can read pages all about fertilizing SIPs. So be sure to check that
resource as well. But let me share what I've been testing and how I typically apply my nutrients.
Some people mistakenly think synthetic time-release fertilizers
won't work in SIPs. Things like Osmocote seem to be off limits in wicking beds. Well,
I've tested these fertilizers and they work just fine. That being said, I really do prefer
organic products. Jobe's and Espoma are two brands worth mentioning.
For years now, I mostly buy bulk bags of Garden-tone and Plant-tone. These include
macro AND micro nutrients. That includes calcium and magnesium. I like Plant-tone because I can
get a larger size. It's a super great value. As a general all around solution for your vegetables,
Espoma Garden-tone works nicely. Jobe's also has an all-purpose which would work great. Some plants
will use extra nitrogen, like corn or kale. For these, the Plant-tone is a great option. On the
other hand if you give tomatoes too much nitrogen, you'll get lots of stems and leaves with very
little fruit. Jobe's and Espoma both have tweaked formulations intended to optimize yield.
Once you select a fertilizer, how much should you use? It's easiest to say:
"Follow the instructions on the label." But that's where things get confusing.
Look at these instructions for Jobe's All-Purpose. For a 2 inch plant, use 1 and 1/2 tablespoons. Ok.
But plants grow. What happens when it's 12 inches? Scratch that. Let's look at the linear feet. For
a 10 foot row use 1 and 1/2 cups. Alright. But what's this down here? It appears you could also
look the pot size. So for a 4 inch pot, use 1 and 1/2 tablespoons. Easy enough. What if we increase
the pot to 16 inches? The volume increases 64 fold. Do we use 64 times the fertilizer? Nope.
The jump from tablespoons to cups is only a 16 fold increase. So in the 4 inch pot,
the nutrients would be 4 times as concentrated versus the 16 inch pot. But wait, that 16 inch
pot gets the same amount of nutrients as an entire 10 foot row of vegetables?
Whaaaaaaat??? Forget this. Is Espoma any better? Here are the
instructions from Garden-tone's PDF label. Here's a printed label from 2017. Same NPK. Let's use
this sample bed and follow the PDF. First we soil prep with 6.7 cups of fertilizer. A week later we
side dress the plant rows with 16.6 cups. And again throughout the growing season. Let's say
3 more times. In the end we've used 73 cups of fertilizer. That's a lot. Is that overkill?
And do you really need to follow a monthly schedule? Why not just do it all at once
and be done? Fortunately my 2017 bag gave instructions based on container volume:
2 cups per cubic foot. This bed has 32 cubic feet so I would need 64 cups. That's a little less than
the other method. Is it still too much though? Why not just try to match a retail potting mix?
Lots of people use Miracle Gro. Sure, some gardeners raise their nose at the brand and parent
company Scott's. But you can't deny the results. In my very, very first year trying to garden
I saw the difference. Throw a pepper in the ground and you get this. Put it in a pot of Miracle Gro
and voilà! This explosion of growth made me so excited,
I never wanted to stop gardening ever since. So what's in that stuff? Just look on the bag.
I can take the total weight of the mix and look at the percentage of NPK. This let's me determine the
weight of macros in a single cubic foot. So how does that application rate for Espoma Garden or
Plant-tone stack up? On a cubic foot basis, it's somewhat comparable. Depending on the macros, some
values might be slightly lower. Or up to twice as much compared to a stock bag of potting mix.
Distilling this all down, leads to this general guideline for blended,
organic granular fertilizers: 1 to 2 cups per cubic foot of potting mix. That assumes the NPK
values are around 3 to 5. This also assumes the soil's been depleted from the previous season.
Certainly this applies to building an unfertilized mix from scratch.
To see what would happen on the high end of this scale, I've been testing my SIPs year after year.
Recording my data. And monitoring plant health. After 5 years of testing, here are some sample
rates from this past growing season. As you see, I've mixed and matched. No issues. Even mixing
time-release with organics has worked great. Quickly, I'll just hone in last year's pepper
crop. I blended three fertilizer types. All together it was about $6 in fertilizer. But my
yield was 44 pounds of peppers. That could easily amount to $160 worth of yield!
So what are my tips for mixing this into the soil? In my SIPs, I use a two prong approach.
For short term crops like lettuce, I use a lower fertilization rate. And I just blend it all into
the top 3 to 4 inches of soil. But for larger and longer lived crops like corn, cucumbers, zucchini,
peppers, watermelon or tomatoes I mix between 1/3 to 1/2 of the fertilizer into the surface.
Afterwards, I bury bands or strips of the remaining fertilizer around and in between
the plants. To do this, carve a trench 4 inches deep with a hand trowel. Evenly pour in the
fertilizer. Then press the fertilizer into the soil so it's 2 inches below the surface. Cover
it over with some of the surrounding mix. Then I plant my crops. Be sure the nutrient bands
are at least 3 inches from the plants roots. What if you're sowing seeds?
Large seeds like squash, melon or corn have germinated fine as long at they weren't too
close to those fertilizer strips. But those nutrients will suck up water and could dry out
sensitive seeds. So either wait to apply the bands after the seedling has gotten established, or just
grow the seedlings ahead of time. What happens though,
is the blended fertilizer acts quickly becoming available to plants early on.
As nutrients get depleted and plants get larger, their roots reach those nutrient bands. Even if
you use purely organic, uncoated fertilizer, the nutrients last much longer, steadily
feeding your crop throughout the season. Are there any finer points to be aware of?
I don't use impermeable mulch, like plastic, over the surface of the soil. I've even stopped
covering my SIP boxes during the Winter. Here in the northeast, we get regular precipitation.
This helps to flush excess salts out of the soil at the end of the season.
Likely this has helped to avoid toxic buildups. If you're in an arid climate, keep this in mind.
You might manually flush the soil surface each season. You could also get a soil analysis every
couple of years to check nutrient levels and salinity. You might opt for the lower,
more conservative fertilization rates and see how the plants respond.
Rotating crops could be a way to balance out nutrient levels. I generally don't do it,
but it's a good option. You could also consider secondary scavenging crops. Heavy feeders
like brassicas could be grown after the main crop as a way to suck up unused nutrients.
This would help to further reset your bed before the next growing season.
Conversely, what if you underestimate the plants' nutrient requirements? Later in the season, leaves
might be yellowing due to nitrogen depletion. A side dressing of fertilizer would help.
But liquid plant feeds can give the quickest results. These work as both root drenches
and even foliar applications. I don't advise adding them to the water reservoir though.
You can use various organic solutions. But honestly, Miracle Gro Plant Food works just fine.
Whatever you decide, pay attention to the NPK values so plants actually get what they need.
I hope this info has helped with your container and SIP gardening. The wicking beds supply lots
of water, as needed. In a good location, your plants can get sufficient light. That just leaves
nutrients. And by supplying what plants need, you can get high density, high yield crops!
Thanks for watching. Please like and subscribe if you haven't. I hope these tips bring you great
success so you have a year of Happy Gardening! Hi. Hi. Your yard always looks wonderful.
I try to stay on top of it. I know. I just, I'm amazed at the size and what you produce.
In a small space, right? Really. Thank-you.