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Knowing how often to water seedlings is an important skill to learn when starting seeds indoors. Too little water can affect germination or cause small seedlings to wilt. Too much water deprives plants of oxygen, encourages fungus gnats, and may prompt issues like damping off. The frequency of watering depends on factors like the size of the seedlings, the growing mix, and the types of containers you’re using. In this article you’ll learn how often to water seedlings grown in cell packs, pots, soil cubes, and more, and how to do it right.
Why it’s important to know how often to water seedlings
Starting seeds indoors isn’t difficult and you can boost your success by learning how often to water seedlings. Just-sprouted seedlings are delicate and both under and over-watering can affect their growth. Here are some ways watering impacts seedling health.
Underwatering issues:
- Reduces seed germination – Too little water may not break seed dormancy so the seeds don’t sprout. Or if the seeds do start to germinate, a very dry growing mix can dehydrate the emerging plants before they break through the soil.
- Wilting seedlings – Seedlings need a consistent supply of moisture and when there is too little water, the roots die and plants wilt.
- Dried up seedlings – If you forget to check your seedlings for a day or two and the growing mix dries out completely, your plants may not survive. Very wilted or dried up seedlings won’t recover.
To learn more about how often to water seedlings watch this video:
Overwatering issues:
- Seeds rotting – Waterlogged growing mix can cause seeds to rot, reducing germination rates.
- Wilting seedlings – As noted above, too little water can result in wilted seedings, but so can too much water. In saturated soil, the spaces around the roots are filled with water. Plants also need oxygen and the lack of air causes the seedlings to droop or wilt.
- Insect, mold, or disease problems – Too much water can prompt a fungus gnat infection or mold to grow on the soil surface. Excess moisture also promotes problems like damping off, whose pathogens thrive in wet growing conditions.
Two ways to water seedlings
There are two watering methods for seedlings: watering from the top or from the bottom. Both options are effective, but there are pros and cons to each. Your choice is based on preference but also how you’re growing your seedlings. For example, seedlings in soil blocks shouldn’t be watered from above as it can case the blocks to crumble. More on top and bottom watering below:
- Top watering – This is the most common way to water seedlings that are growing in pots, cell packs, and plug trays. For the first week or two I top water the growing medium by misting with a spray bottle. This keeps the surface of the growing mix moist to promote good germination. Once the seeds sprout, I switch to a watering can.
- Bottom watering – Bottom watering seedlings isn’t difficult, but does require more time and attention than top watering. It uses capillary action to move water from a tray into the growing mix. You must use containers or seedling trays with no holes to prevent water spillage. Once the growing mix is saturated, you have to check the tray and pour out any excess water. Bottom watering can reduce the occurrence of plant diseases as you’re not getting the foliage wet.
Essential tools for watering:
When it comes to watering seedlings, there are a few tools you can use and it’s not one-size-fits-all. For example, I use different watering tools for different stages of growth. Here are four common types of watering tools:
- Watering can – A watering can is essential and I recommend buying one with a removable rose attachment. This has tiny holes and creates a gentle shower, perfect for small seedlings. For sturdier seedlings I swap out the rose for a spout attachment. This lets me direct water exactly where I need it.
- Hand mister – Also called a spray bottle, a hand mister has an adjustable nozzle and allows you to mist small seedlings. Spray bottles are great for the first few weeks of watering, but once the seedlings size up and a larger volume of water is needed, it’s time to switch to a watering can.
- Seedling sprayer – This is a unique tool that is part watering can and part spray bottle. It has a soft silicone bulb and a spraying rose. To fill it, squeeze the bulb to remove air and place the rose in a container of water. As you release the bulb, it sucks up water. When the bulb is full, use it to gently irrigate seedlings. It’s handy, but isn’t the right tool if you have a lot of seedlings because most seedling sprayers only hold about a cup of water.
- Indoor garden hose – If your seed-starting area is close to a sink you can use an indoor garden hose. These are often coiled to save space and fit overtop a faucet for easy watering.
The best water for watering seedlings
When filling up watering cans or hand misters, use lukewarm or slightly warm water. Very cold water can shock young seedlings or delay germination of seeds. You also don’t need to buy special water, like distilled water, for seedlings. Municipal tap water, as well as well water, that is safe to drink is fine for seedlings.
Factors that impact how often to water seedlings
Ok now that we’ve looked at watering methods and tools, it’s time to talk about how often to water seedlings. Frequency of watering depends on factors like the size of the container and the temperature of the room. Here are 5 points to consider:
1) Container size:
It’s a fact, smaller containers dry out quicker than larger containers. That means you’ll have to water cell packs and plug trays more often than larger pots.
2) Container material:
The growing mix in containers made of natural materials like peat or coir dries out faster than that in plastic pots. These porous materials wick moisture from the soil making it extra important to play close attention to watering.
3) Type of potting mix:
There are many types of growing mixes you can use for seed starting. The two main options are seed-starting mix and all-purpose potting mix. The peat in seed-starting mixes is more finely milled, so it’s lighter and less dense. Both types of mixes contain ingredients like perlite and vermiculite, and, depending on the product, compost. I use an all-purpose mix as I start a lot of seeds and it’s usually more cost-effective than seed-starting products.
4) Growth stage:
The root systems of seedlings, especially just after germination, aren’t well developed and therefore the plants don’t need a lot of water. For the first few weeks you’ll water once or twice a week. As the plants grow and use more water the growing mix dries out faster. You’ll need to irrigate more frequently and with a larger amount of water.
5) Temperature of the room:
I grow most of my seedlings under grow lights in my basement. This space is kept cooler than average room temperature and because of this water doesn’t evaporate as quickly. If you’re growing seedlings in warm temperatures, like a sunny window, the growing medium dries out faster and you’ll have to water more often.
How often to water seedlings
For most types of vegetable, flower, and herb seedlings, the goal is to maintain a lightly moist growing medium; not too wet and not too dry. This may sound like a balancing act, but trust me, it’s not difficult once you’ve got the hang of it. The most important point is to check the growing mix daily, watering when necessary. You can do a visual check to see if the soil looks dry, but it’s best to feel it with your finger to get a more accurate reading on the moisture level. Below is a guide that outlines how often to water based on whether you’re using cell packs, plug trays, peat pellets, pots, or soil blocks.
How often to water seedlings in cell packs and plug trays
Growing seedlings in cell packs is a space effective way to start seeds. Cell pack sheets fit perfectly in 1020 trays, preferably those without holes to prevent water spills in your seed-starting area. The size of the individual cells varies depending on the type of cell pack or plug tray you are using and smaller cells dry out faster than larger cells. However uneven watering or having a fan in the room, can cause some of the cells in the tray to dry out quicker than others. This means you’ll have to spot water the dry cells using a watering can with a spout attachment. I try to give each cell the same amount of water every time I irrigate.
Generally, I water seedlings growing in cell packs and plug trays once or twice a week for the first two to three weeks. As the seeds germinate and the young plants size up, watering becomes more frequent.
How often to water when growing in peat pellets
Seed-starting pellets are compressed disks of peat moss or coco coir that are surrounded by a mesh netting. When you’re ready to sow seeds you first need to hydrate the pellets by saturating them with water. I place them in a tray and add warm or room temperature water until they expand their full size. This typically takes 8 to 10 minutes. When the pellets have fully hydrated, plant the seeds.
As with potting mixes and seed-starting mixes the goal is to maintain a lightly moist growing medium for the seedlings. I find seedlings grown in peat pellets dry out quicker than those in cell packs or plug trays. Again, use your finger to feel the top of the pellet to gauge whether it’s time to water.
I bottom water peat pellets by adding a half inch of water to the tray. Once this is absorbed, I check the growing mix to see if it’s fully dampened. If it’s still dry, I add more water. When the pellets are evenly damp, I drain out excess irrigation water and place the tray back under my grow light. You can also top water peat pellets using a watering can. Make sure to thoroughly wet them so there are no dry spots in the growing mix. Expect to water two to three times a week as the seedlings grow.
How often to water seedlings in pots
For fast-growing plants like squash and pumpkins I start the seeds in 4 inch diameter pots which offer plenty of root space for the vigorous seedlings. Pots hold a larger volume of growing mix than cell packs, plug trays, and peat pellets. For this reason, bottom watering isn’t the best way to water. You’d need to put the pots in a deep container or bucket in order to get the full effects of the capillary action of bottom watering. Instead I top water using a watering can. When the seedlings are very small I use a rose attachment, but once they’ve sized up and have several sets of true leaves, I switch to a spout attachment.
Because pots dry out slower than small cell packs and plug trays, you’ll have to water less often. Depending on the size of the plant and temperature of the room, likely one to two times a week.
How often to water when growing in soil blocks
Soil blocking has become my go-to way to start seeds. It’s easy, uses less plastic, and produces healthy, vigorous seedlings ready for the garden. The technique for watering soil blocks, however, differs from watering seedlings grown in cell packs or pots. For the first week or two I use a hand mister to keep the top layer of soil damp, spraying the growing mix every few days. By week 3 I’ve switched to bottom watering. If you top water soil blocks using a watering can, they’ll crumble. You want them to maintain their shape and not collapse into piles of growing mix. I use a watering can with a spout attachment, directing water into the tray holding the soil blocks. Add enough water that the blocks are saturated.
Allow the soil cubes to dry to the touch before watering again, but not so much that the plants wilt. In average room temperature you’ll need to water soil blocks two to three times a week once the seedlings have several sets of true leaves. Read more about soil blocking and get my how-to guide.
How often to water when growing in biodegradable containers
There are many types of biodegradable containers you can use to sow seeds indoors. These include egg cartons, toilet paper tubes, peat pots and strips, and coconut coir pots. These porous types of containers dry out much faster than plastic cell packs, plug trays, and pots. You can top or bottom water seedlings in biodegradable containers. The key to success is to maintain a lightly damp growing mix so expect to water three to four times a week.
How often to water seedlings in the garden
Perhaps you’re wondering how often to water seedlings outside in the garden. As with indoor grown seedlings you want to make sure that you’re supplying enough water to promote healthy plant growth. Whether they’re transplants or direct sown, outdoor seedlings are exposed to sun, wind, and warm temperatures which cause the top layer of soil to dry out quickly. I check my vegetable garden daily, giving seedling beds a good soaking when the soil is dry a half inch down to ensure adequate moisture. Use your finger to gauge soil moisture.
It’s best to water with a hose nozzle that has a shower attachment so the seedlings aren’t damaged by a hard jet of water. If the weather is cloudy or damp, you may not have to water for a few days. As the plants grow, you can reduce how often you water to once or twice a week as needed.
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