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Bottom Watering Seedlings: A Complete Guide

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Bottom-watering seedlings is a great way to ensure that they are getting the required amount of water to grow healthy. It takes the guesswork on how much to water because you can overwater once done correctly.

Bottom watering seedlings promotes strong and healthy plant growth by allowing the entire root system to access the applied water that has been distributed evenly within the soil. The other benefit of bottom watering seedlings is that it prevents overwatering and the pests and diseases that come with it.

Seedlings when watered from the bottom can be a tricky task, but it is well worth the effort. Seedlings need water to grow, and if they are not watered correctly they can eventually die.

This article will help you learn how to properly water your seedlings so that they have the best chance of surviving and growing.

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Related Posts that are helpful –
Bottom watering vs Top watering
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What is Bottom Watering?

Plant absorbing water from bottom watering

Bottom watering is the process of irrigating plants and seedlings from the base of the plant. Bottom watering is an easy and affordable way to grow plants because the water can be directly applied to plants with little waste. 

When seedlings are watered from the bottom the water travels up through the soil with capillary action.

The water is then able to distribute evenly throughout the seedlings soil structure, supplying all the roots with an even amount of water.

Gravity keeps water from gathering in one place for any given period of time.

When removed from the bottom watering tray, whatever excess water that was hung up is then allowed to drain freely away from the soil leaving only the water that the soil has ?soaked up? during the watering period.

This method of watering also helps prevent overwatering by not supplying the plant with a potentially excessive amount of moisture.

Too much water can harm seedlings and cause the roots to rot. Watering from the bottom is an easy way to avoid this problem.

How to Bottom Water Seedlings?

Bottom watering takes a little more time than conventional top watering, but is totally worth the time and effort to prevent the effects of overwatering.

With that being said, seedlings are at a very delicate stage of their life cycle and any type of stress can lead to unwanted disaster. 

This is why we recommend bottom watering and we have outlined a step by step guide on how to correctly bottom water your seedlings so that they will emerge as strong and healthy plants.

Steps for Bottom watering seedlings –

  1. Obtain a flat open tray which is larger than the size of the seedling tray.
  2. Place your seedling tray on the flat open container for bottom watering
  3. Fill the container with 1 inch of water
  4. After 15 to 20 minutes remove the seedling tray
  5. Remove the excess water from the flat container 
  6. Place the seedling tray back into the empty container to allow excess water to drain out for 10 minutes.
  7. Remove the plant tray

Note: The time taken to bottom water the plant should be enough to allow the water to reach to the surface of the soil. You can deem the bottom watering process completed when the top of the soil is moist to the touch.

level in bottom watering tray

What to Look out for

Different types of soil mixes would have different absorption rates depending on the ratio of amendments and organics within the soil.

Plants would have varying soil requirements depending on the species, which is why you should inspect the seedling soil to determine how well it would absorb water. But that’s just sight. 

The real test is to try the bottom watering method and observe how well or how fast the soil absorbs water. This way you can determine how long you should leave the seedlings within the watering tray.

The Benefits of Bottom Watering Seedlings

The overall benefit of bottom watering seedlings is that they emerge as healthy as possible from this delicate stage.

Other benefits of bottom watering seedling include –

Promotes Healthy Root and Plant Growth

As water is applied to the bottom of the seedling?s soil system this prompts the roots to grow deep into the soil and spread more evenly through the structure.

When this happens the roots of the seedling will be able to access more nutrients from the surrounding soil.

What this eventually equates to is a more healthy and stronger seedling plant. It greatly increases their survival rate when placed in the open garden environment when they are matured enough.

Prevents Overwatering

As previously discussed, bottom watering only applies the required amount of water to the soil by capillary movement. 

The soil absorbs the water it needs after which the excess is drained out by gravity. The seedling roots can now absorb the nutrients and water from the surrounding soil.

Prevents Root Rot

As you may know root rot is caused by overwatering conditions where all the air spaces between the soil is filled to capacity with water.

This excessive amount of water stifles the roots of the plant of oxygen. With the lack of available oxygen, root rot is characterized by dark brown to black roots. 

Plants lose vigour, become stunted and yellow, and may wilt or die back and drop some leaves. They do not respond to fertilizer and water.

By supplying only the required amount of water, bottom watering solves this problem.

Prevents Pest and Fungus Growth

By limiting excessively damp and overwatered conditions, bottom watering seedlings retards the environment that would normally support the growth of fungi and pests like fungus gnats.

When fungus thrives they attract the small fly-like fungus gnats which like to feed on them. The gnats also like damp conditions and they will feed on the roots of the seedlings eventually causing it to die.

Regulates Humidity

When seedlings are bottom watered the amount of moisture surrounding the plant will be less but just the right amount to help the plant thrive within their environment. 

Excess humidity can lead to moisture loving fungus to set in which will directly affect the seedlings health and development.

Bottom Watering Vs Top Watering

Bottom Watering Vs Top Watering

Bottom watering plants keep the soil uniformly moist so the entire root structure gets watered while Top watering encourages the presence of fungus and gnats while the water can be channeled out of the soil, not being able to reach the entire root structure.

Experts recommend that a garden requires about one inch of water every seven days and the soil structure should be kept healthy to enable the plant to absorb water efficiently. 

Bottom WateringTop Watering
Prevent overwateringDoes not prevent overwatering
Water is applied uniformly to the soilWater can channel
(not reaching all the roots)
Can help control humidityDoes not help much with humidity
Prevents splashing of soilCan cause soil to splash
Prevents fungus and pest infestationCan apply water to leaves where fungus can thrive
Prevents root rot conditionsCan promote root rot with overwatering

When to Bottom Water Seedlings?

When bottom watering seedlings, it will be smart to consider the time of day to apply water from the bottom.

The best time of day to bottom water your seedlings is during morning periods between the hours of 6am to 9 am and on late evenings between the hours of 5pm to 6pm.

This is because during this time the humidity in the air and surrounding environment is lower so less water is lost to the atmosphere as time passes. 

These times are suggested for seedlings that are not germinated with a humidity dome.

Although it is a widely used practice to use a humidity dome for seedlings, it is not required. The seedlings will still germinate.

On the other hand a humidity dome keeps the soil moist for a longer period of time and it also promotes germination rates.

With this exception, when using a humidity dome bottom watering can be done anytime during the day.

How often to Bottom Water Seedlings?

Seedlings can be bottom watered one time each day either in the morning or the evening period when the surrounding humidity is higher.

However, the best indicator that your seeds or seedlings need water is how dry their growing medium is. When you touch the soil, it should neither feel soggy or too dry. Instead, it should feel like a moist sponge.

If you have watered the seedlings during the morning period and found that the soil is dry, you can water again within the same day. 

The general rule is to keep the soil moist. 

As previously stated, the use of a humidity dome helps prevent the problem of the soil drying out too quickly by keeping the environment around the seedling humid for a longer period.

Bottom watering seedlings

Best water for seedlings when Bottom Watering?

The best water for seedlings is distilled water or rain water. 

Distilled is basically the purest form of water as all the minerals within the water have been removed through boiling. The pure water becomes steam, which is collected in a flask after the steam has condensed.

Rain is by far the best type of water that you can give your plants. It is full of minerals that are necessary for plant growth, and will make your plants grow bigger and healthier than any other type of water.

Rain water is also slightly acidic with a pH ranging between 5 to 5.5. This slight acidity helps nutrients within the soil to mobilize fast which means more nutrients will be delivered faster to the seedlings which will be reflected in increased growth rate.

Alternatively, tap water can be used but that is dependent on the quality of the water in your area. 

Most tap water should be fine for your houseplants unless it is softened because it has salts that can build up in the soil over time and eventually cause problems. 

Chlorinated water is also safe for most houseplants, but if you have a filtration system, that’s even better for your plants.

Applying fertilizer when bottom watering

Seedling may have to be fertilized depending on the plant variety and nutrient requirement. 

Adding fertilizer when bottom watering can allow the seedling to efficiently absorb the nutrients that are applied to it as the entire root system will be able to access the nutrients from the fertilizer.

The application of fertilizer in this way requires the fertilizer to be of a water soluble type. The fertilizer is firstly dissolved fully into the water before it is added to the watering tray.

It then follows the same watering time according to the method stated above.

See our more detailed article on how to bottom water with fertilizer.

The Takeaway

Bottom watering is the best way to apply water to your seedlings. 

It provides them with a steady supply of nutrients and water that they need as their roots develop, without exposing them to risks like fungi or bacteria growth. 

The benefits of bottom watering greatly outweighs the traditional method of top watering. One of which is the fact that it’s almost impossible to overwater your seedling which can cause a lot of pests and disease to thrive.

This article has given you all the information about when, how often and how to add fertilizer when bottom watering your seedlings to ensure you have success when transplanting them into your garden.

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