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Whether in pots or in the garden, baby plants are very fragile in their early stages of life. They need the perfect balance of water, sunlight, and fertile soil to grow into strong, high-yielding crops.
Once you’ve planted seeds in the perfect seed-starting mix and sturdy, well-draining cell trays and placed them in the sunlight, your irrigation schedule can make or break your seedling success:
- With too little water, seedlings can quickly dry out, leading to poor germination.
- If you overwater, your seedlings become prone to damping off, and other issues.
- Optimal soil moisture will help plants build strong roots and better germination.
Knowing precisely how much moisture your seedlings need to thrive can be challenging. Let’s dig into how you can determine the amount and frequency of irrigation for garden seedlings this season!
The Short Answer
Most seedlings require water every day or every other day. First, check the soil moisture using your finger by checking the soil color near the drainage hole. If the soil feels or appears dry or brittle, irrigate thoroughly until water pours out of the bottom of the tray, then stop. If the soil is only a little dry, give the seedlings a sprinkle of water to keep them moist until the next deep watering.
The Long Answer
We all wish there was some special trick for watering vegetables, like “Give each plant ½ cup of water daily for the first month.” Unfortunately, this approach is over-simplified and will not work for every vegetable crop.
You cannot assume that every seedling needs the same watering frequency as its neighbor. Each crop, garden bed, and seed-starting setup is too unique to make such broad generalizations. Instead, you can rely on your observation skills to assess when to water.
Check Seedlings Daily
There is no “one size fits all” approach to watering seedlings. The only broad-sweeping rule we can stand behind is: The best gardeners check on their seedlings daily.
This means that seed-starting season is not the time to go on vacation! Your garden plants are the neediest in the first 3-5 weeks of their life. You only need a simple 5-10 minute examination of your greenhouse, windowsill seed trays, or direct-sown garden beds.
Finding a balance between underwatering and overwatering is essential. Irrigation is mainly based on crop type and environment. No specific volume or timing can be applied to all baby plants.
The exact amount or frequency of water depends on 5 key factors:
| Cell/Container Size | The soil in smaller containers or cell trays tends to dry out more quickly than in larger pots. Water your large plants less frequently. |
| Seedling Age | Newly germinated seeds typically need more water than older seedlings with established roots. Maintain continuous moisture for germinating seeds, then cut back to watering every other day or every few days once the seedling has true leaves. |
| Soil Type | Soil blends and seed-starting mixes with higher organic matter (like peat moss, coco coir, or compost) tend to hold onto water for longer periods. |
| Temperature | Warm climates or hot greenhouses will naturally dry out the soil surface more quickly through evaporation. Seedlings in colder areas don’t usually need as much water. |
| Humidity | Dry areas tend to accelerate the speed of soil drying in and around a seedling’s roots. On the other hand, high humidity is typically correlated with reduced watering frequency. |
Take all these factors into account when watering your seedlings. Remember, while you can use a moisture sensor, the only fool-proof way to perfectly irrigate seedlings is through observation.
How to Check Soil Moisture
Hobby gardeners can learn a very valuable lesson from professional farmers and growers— the art of observation! A nursery grower never waters their greenhouse until they have examined the moisture levels in the different plants. A farmer never irrigates their fields until they have checked the recent rainfall, temperatures, and soil water level.
The best thing you can do for your seedlings is check the soil before you water! Here are a few time-tested methods:
Finger Test
Don’t be afraid to get your hands dirty! If you are germinating seedlings in the garden, it is essential to feel the soil before you water. Generally, you only need to put your finger an inch or two deep to determine how much water the seeds need:
Too Dry
If your skin comes out perfectly clean with no soil stuck to it, the soil is far too dry! Water your seeds immediately and cross your fingers that they haven’t been dired out for too long. Do a deep watering that allows the water to penetrate into lower layers of soil or drip out of the bottom of the container(s).
Just Right
If your skin comes out slightly dirty, this probably means that the soil is at a pleasant level of moisture. The seeds can breathe and drink freely. You may sprinkle a little bit of water on top, but avoid any heavy irrigation.
Too Wet
If your finger has lots of soil caked onto it like brownie batter, your soil is probably soggy and waterlogged. The seedlings may be suffocating under the excessively moist conditions. Let them dry out for a day or two before irrigating again.
This method does not work very well for seedlings in small cells or pots because sticking your whole finger into the container could disrupt the root system. Instead, touch just the top centimeter of soil or use another method.
Checking the Soil Surface
If you don’t trust the finger-trick or your cell trays are too small to fit your hand into, it’s time to use visual cues. You can tell a lot about the moisture level by simply looking at a seedling and the soil it is growing in…
Too Dry
Seedlings growing in soil that is cracked or powdery are sure to be unhappy. They might look wilted or weak. The dry soil appears pale, grainy, gritty, or dusty. The seedling needs water immediately. Beware that the soil may have become “hydrophobic” (it will repel moisture), so you may need to give it more water than usual in order to rehydrate.
Just Right
Perfectly moist soil should look loamy, crumbly, breathable, and moderately dark in color. However, the appearance will depend on the type of soil or seedling mix you use. You may have to gauge your specific soil type over time. Notice that happy seedlings look vibrant, upright, and hydrated.
Too Wet
If algae or mold is growing on the soil surface, it is a sure sign that you are overwatering! The seedling is probably suffocating in the soggy environment. It may have a wilted or yellowing appearance.
Cut back immediately and let the soil dry out. You can lightly rake the soil surface to aerate it. Consider removing the upper layers of algae or mold using gloves and then spraying with a diluted neem solution to prevent fungal infections.
Be sure to lift up your seedling pots and check the soil appearance near the drainage hole as well.
Try Forming a Soil Ball
The final method for checking soil moisture is the “ball method.” You can use this when filling seed-starting trays, checking moisture in a square seedling pot, or monitoring seedlings in your garden beds.
Pick up a small amount of soil and roll it between your hands to create a ball. Notice how the soil sticks to itself…
Too Dry
The soil won’t hold together at all and may crumble or fall into dusty pieces. You can feel the gritty particles of soil between your fingers. Seedlings likely need water ASAP.
Just Right
The soil may hold a loose ball shape and lightly fall apart when pressed together. It sticks to itself a little bit but doesn’t feel like Play-Doh. The perfect moisture level is crumbly, loamy, and pleasant to the touch.
Too Wet
The soil feels sticky and forms a soggy climb that may leak water out when squeezed. Seedlings probably need to dry out and get more aeration in their root zone before the next watering.
How to Water Seedlings
You’ve finally mastered the art of checking soil moisture, but now you need to actually give your seedlings a drink!
Many gardeners don’t realize that their watering methods could be stalling their plant growth. Baby seedlings are particularly prone to toppling over or losing their root stability.
Newly germinated seeds can even float away when they are watered too harshly! Here’s how to avoid flooding seedlings with big blasts of water.
Hose Watering
A garden hose is the easiest and most efficient way to water outdoor seedlings or plants in your nursery. You can even move your indoor seedlings onto the patio to water and then bring them back inside once they have drained.
When irrigating seedlings with a hose, remember to:
- Use a fan nozzle to spread out the water like a pleasant, even rain.
- Check the water pressure on the ground before putting it over your seeds.
- Never hold the hose in one place for too long.
- Maintain a continuous flowing movement of water over the seedlings.
- Hold the spray nozzle at least 1-2 feet away from the seedling surface.
Using a Watering Can
If you only have a few seedlings, a watering can is the cheapest, most accessible way to irrigate.
When watering with a can, remember to:
- Choose a watering can with a wide fan-like nozzle.
- This will help distribute water evenly over the soil surface.
- Avoid dumping large amounts of water in one place.
- Let water drain before adding more.
- You don’t want to flood seedlings with moisture too quickly.
Drip Irrigation
When direct sowing into your garden, drip irrigation is an efficient and passive way to slowly deliver water straight to the root zone of your plants. It prevents wasted water while also keeping weeds at bay. Instead of watering a whole garden bed, drip lines bring the irrigation to your crops only.
When using drip irrigation, remember:
- Your seedlings need to be planted in lines or rows for this method to reliably work.
- Lay drip lines about an inch from the stem of the seedlings.
- You need to set an irrigation timer or a timer on your phone to monitor the lines.
- Start by running the drip lines for 30 minutes to an hour, then check the soil moisture.
- Drip irrigation does not work as well for germinating seeds.
- Use overhead hoses or sprinklers to germinate the seeds.
- Start using drip lines to supply them with moisture afterwards.
Bottom Watering
If you feel uncertain about your watering capabilities, you may want to try out bottom watering. Bottom watering is the easiest way to prevent overwatering. This method waters seedling trays and potted plants from the bottom-up.
Capillary action makes bottom watering possible. This intriguing phenomenon explains how plant roots and soil defy gravity by bringing moisture up to the roots. The process of adhesion and cohesion of soil and water particles allow the moisture to “climb” up to plant roots.
To bottom water your seedlings, follow this simple process:
- Find a bowl, catchment saucer, or closed tray and fill it with a couple inches of water.
- Place your cell tray, 6-pack, or seedling pot inside the tray.
- Allow the soil and plant to work their magic as they draw the moisture upward.
- Check the moisture every 10-15 minutes.
- Once the top appears damp you can dump the catchment tray.
Keep in mind that this method only works with seedlings that have developed true leaves and a modest root system. Their containers must have drainage holes from which the plant can suck up moisture like a straw. Do not use bottom watering on newly germinated seeds; they are likely growing too close to the surface.
Final Thoughts
The philosophy of watering seedlings may seem complicated, but the daily activity is very simple. Once you get used to your specific plants, soil, and climate, your watering schedule will likely take just 5-10 minutes per day. When in doubt, check your plants on a daily basis and err on the side of caution to prevent overwatering.
