One of the advantages of an AutoPot system is that plants are fed from the bottom up. Once the system is established, water and nutrients enter the tray through the AQUAvalve and are drawn upward through the substrate as the plant needs them.
Most of the time, anything you plan to feed your plants can simply be mixed into the reservoir, provided it is clean, fully soluble and suitable for use in an AutoPot system. However, there are situations where you may want to supplement your normal feeding program with a product that you do not want sitting in the reservoir, pipework or AQUAvalve.
That’s where tray feeding comes in.
What is Tray Feeding?
Tray feeding is exactly what it sounds like: instead of adding a supplemental product to the reservoir or pouring it over the top of the pot, you temporarily shut off the AutoPot system and apply the solution directly to the tray.
The plant then takes up the solution from the bottom in essentially the same way it normally feeds through the AutoPot system.
This gives you a simple way to introduce certain supplements while keeping them out of your reservoir and irrigation lines.
When Should You Tray Feed?
One of the most common reasons to tray feed is when you’re running a mineral or salt-based nutrient program through the reservoir but occasionally want to supplement with an organic product, microbial inoculant or another additive that you’d prefer to keep out of the reservoir.
You might be tempted to simply top-feed that product into the pot. Once an AutoPot has been established and is actively bottom feeding, however, we generally recommend against doing that.
Why Not Just Top Feed?
When mineral nutrients are supplied from the bottom, water and nutrients move upward through the substrate. As moisture moves upward and evaporates from the upper portion of the pot, unused mineral salts tend to migrate with it and accumulate toward the top of the substrate.
This is a normal characteristic of bottom-fed growing and generally isn’t a problem. The upper portion of the substrate remains relatively dry, while the plant develops an active root zone around the consistent moisture and nutrient availability below. Since the top portion of the substrate remains dry, roots stay out of that area where the salts accumulate.
If you suddenly begin top-watering an established bottom-fed plant, however, you’re changing that environment.
Several things can happen:
- Accumulated salts can be dissolved and carried downward into the active root zone, potentially causing a sudden increase in EC. This is one of the biggest concerns when top feeding a mineral-fed AutoPot.
- The moisture distribution can change suddenly, saturating areas of substrate that normally remain relatively dry.
- Nutrients that have become concentrated in different areas of the substrate can be redistributed, temporarily changing nutrient availability and root-zone EC.
- Depending on how heavily you top water, you can temporarily reduce root-zone oxygen by saturating more of the substrate than would normally be wet during an AutoPot irrigation cycle.
It’s sometimes said that switching from bottom feeding to top feeding can “confuse” the plant. That’s not really what’s happening. The plant can take up water and nutrients wherever its roots encounter suitable conditions. The concern is that you’ve spent weeks or months establishing a relatively stable bottom-fed root-zone environment, and suddenly top watering can disrupt that balance.
That’s why, once an AutoPot system has been turned on and the plant is established on bottom feeding, we generally recommend continuing to feed from the bottom rather than switching back and forth between bottom and top feeding.
Tray feeding allows you to introduce a supplemental product while maintaining that bottom-fed approach.
How to Tray Feed in AutoPot
The process is simple:
- Prepare your solution. Mix the product in a separate container according to the manufacturer’s instructions. Don’t add it to your AutoPot reservoir.
- Turn off the reservoir. Close the valve supplying water to your AutoPot system.
- Allow the trays to dry. Give the plants time to consume the remaining solution in the trays and for the substrate to dry back a bit to increase absorbency. Around 12 hours to 1 day is generally sufficient, although timing will vary depending on plant size and environmental conditions.
- Add the solution directly to the tray. Using a small watering can or jug, slowly pour the prepared solution into the AutoPot tray next to the AQUAvalve — never directly on top of the AQUAvalve.
- Fill to the normal tray level. Add solution until it reaches approximately the point where the supply tubing enters the tray. Do not overfill the tray.
- Allow the plant to consume the solution. Depending on plant size, this may take approximately 5–60 minutes. Repeat the feeding if necessary. For supplemental applications, 2–3 tray feedings may be appropriate depending on the product and feeding program.
- Finish with plain water. Once the supplemental feeding is complete and the tray has been consumed, add a small amount of plain water to the tray next to the AQUAvalve. This helps rinse the tray and AQUAvalve area and confirms that everything is flowing normally.
- Let the tray dry again and restart the system. Once the water has been consumed, turn the reservoir back on. There is no need to wait another 12 hours before restarting the system.
Never Pour Solution Directly on the AQUAvalve!
Whenever you’re tray feeding, pour the solution beside the AQUAvalve rather than directly over it.
The AQUAvalve is designed to precisely control the water level within the tray. Slowly adding your solution alongside it allows the tray to fill normally without unnecessarily pouring concentrated nutrients, organics or microbial products directly over the valve mechanism.
If you pour your solution directly on top of the AQUAvalve, you can disrupt its cycling ability and may have to reset your trays.
What Types of Products Can Be Tray Fed?
Tray feeding can be useful for products you want to use occasionally but don’t necessarily want sitting in your reservoir or traveling through your irrigation lines.
Examples include:
- Liquid microbial products
- Biological inoculants
- Certain organic supplements
- Thick or potentially sediment-forming additives
- Occasional supplemental feeds that aren’t part of your normal reservoir nutrient program
Always check the manufacturer’s application instructions before using a product this way. Tray feeding solves the delivery issue, but the product still needs to be appropriate for your plants, substrate and overall nutrient program.
Not All Organic Products Need to Be Tray Fed
It’s important to make one distinction: just because a product contains organic ingredients doesn’t automatically mean it needs to be tray fed.
AutoPot pipework and the inlet to the AQUAvalve are considerably larger than the narrow irrigation lines and drip emitters used in many traditional irrigation systems. Because of this, AutoPot can accommodate certain products containing organic ingredients that might be more problematic in a conventional drip system.
For example, products such as Head Masta from CX Horticulture, Emerald Goddess from Emerald Harvest or C4 from Mills contain organic ingredients but can generally be used through an AutoPot reservoir when properly mixed. On the other hand, products such as B-52 from Advanced Nutrients, thick humic acid products, molasses-based additives or anything particularly viscous or prone to leaving residue are better candidates for tray feeding.
There isn’t necessarily a hard line between the two. A lot comes down to the viscosity, solubility and consistency of the product, along with some intuition and common sense from the grower.
If a product mixes cleanly, remains well dispersed and flows easily, it may be perfectly suitable for reservoir feeding. If it’s thick, sticky, settles out or leaves significant residue, tray feeding is the safer option.
This is one area where AutoPot has an advantage over many traditional irrigation systems. You’re not automatically limited to perfectly clear mineral nutrients simply because you’re feeding through irrigation lines. The larger flow paths of the AutoPot system allow growers to use a wider range of inputs, while tray feeding provides another option for products you’d rather keep out of the reservoir and AQUAvalve.
What About Living Soil?
Living soil is a little different.
With an AutoPot living-soil grow, the goal is generally to establish the system and allow the soil to remain consistently hydrated from below. Repeatedly switching between top and bottom feeding changes the moisture profile you’ve established within the container.
If liquid supplementation is necessary after the AutoPot system has been activated, tray feeding provides a way to introduce an appropriate supplement from below while maintaining the system’s normal bottom-fed operation.
Dry amendments and top-dressing feeding styles require a different approach, so those should be considered separately from the tray-feeding method described here. We will have a separate post about dry amendments and top dressing soon.
The Bottom Line...
If you’re running nutrients through your AutoPot reservoir and everything you’re using is clean, fully soluble and reservoir-safe, there’s usually no reason to complicate things.
And remember, organic doesn’t automatically mean it needs to stay out of your AutoPot reservoir. Some organic-containing products flow through the system without issue. The better questions to ask are whether the product is soluble, how viscous it is, whether it stays well mixed and whether it’s likely to leave behind sediment or residue.
If you’re comfortable with the product moving through the system, reservoir feed it. If it’s thick, sticky, sediment-forming or simply something you’d rather keep out of your reservoir and pipework, tray feeding gives you another option.
Most importantly, tray feeding allows you to introduce supplemental products while maintaining the bottom-fed environment the plant has become established in, without top watering and potentially redistributing accumulated salts, moisture and nutrients through the root zone.
Reservoir feeding for products that can safely travel through the system. Tray feeding for the ones you’d rather keep out. Once your AutoPot is established and bottom feeding, keep feeding from the bottom.