How To Speed Up Germination

Many seeds can take weeks, if not months, to germinate. This can create a lot of difficulty and uncertainty for home-growers, particularly those with short seasons or who are short on space or those growing plans that take a long time to establish or fruit.

You can speed up germination by placing seeds in a warm environment (a minimum of 7°C / 45 F) with high humidity (around 95% RH) and determining if you should provide light or dark conditions for the particular seed. Pre-soaking seeds or using the paper towel method can make germination faster too.

By altering your germination method or making the following changes to the seed’s environment, you can make your seeds germinate much much faster.

Which Method Germinates Seeds The Quickest?

The paper towel method is usually the fastest way of getting a wide range of seeds to germinate. By putting seeds in contact with a moist surface in a sealed container, you provide the most favourable conditions for seeds to take-up water and reach the necessary moisture content for germination.

The paper towel method also enables you to easily check on the seeds – removing the need to dig around on the soil to find out if a seed has germinated or, instead, rotted. This makes it great for viability testing of old seed and ensuring that you have the correct number of plants.

Being locked away in a plastic tub or Tupperware also means they can be easily stacked near a heat source, making them a space-efficient way of germinating seeds.

The paper towel method is often used for larger seeds like sweetcorn, squashes and runner beans. It is recommended that you soak them in a wet paper towel for a few days until a root starts to emerge, and then you can plant them directly in the soil before the shoot appears.

However check on your seeds regularly as you will need to plant them as soon as you see the root emerging so that the root and stem grow in the correct orientation to one another and the ground, and so that the seedling has access to the nutrients it will need to grow.

Is It Better To Soak Seeds Before Planting?

While soaking seeds can speed up germination, it also alters the environment in other ways such as preventing airflow around the seed and limiting oxygen exchange. It can also cause other issues such as making some seeds hard to handle and increasing waste or making some seeds turn to mush.

Therefore you shouldn’t try and germinate seeds directly in water.

However immersing seeds in water, allowing them soak-up moisture and then sowing seeds before they have germinated can greatly speed up germination. This is known as seed priming and is common practice for slow germinating seeds such as peppers and tomatoes.

For seeds like tomatoes and chilli peppers the advice is to soak seeds in tea for a few hours or overnight. The idea is that this helps the seed coat absorb water, swell and ferment but the tannins in the tea supposedly help the seed coat chemically break down via a different mechanism which helps speed up germination.

Soaking seeds for about 24 hours hasn’t appeared to cause any negative effects in my experience, however soaking seeds for too long can begin the rotting process so many people will advise that you do not soak seeds for longer than 48 hours.

Using Heat To Speed Up Germination

Most seeds are built to stay dormant over winter and wait until spring to germinate so that they take advantage of the rising temperatures. So sowing seeds and leaving them on a cold windowsill is a recipe for slow germination, particularly if you are growing heat-loving plants like tomatoes and chilli peppers or slow germinating plants like ground cherries. In fact, most seeds won’t germinate at all below 7°C/45°F.

To speed up germination, place seeds near a gentle heat source. You can cover a radiator with blankets and put your seeds on top, use an airing cupboard or place your seeds above a mantle-piece. Alternatively you could buy a heat mat and directly control the soil temperature.

If you have a south facing window and well-insulated windows, then placing seeds on a windowsill may also do the trick later in the season when there are more sunlight hours and temperatures are higher. I use a shelf above a boiler flue during January and February and swap to a west-facing windowsill from mid-March onwards.

Seeds won’t germinate if it’s too cold but some seeds won’t germinate if it’s too hot either. Around 18°C/64°F is ideal for many annual plants.

And if you are using heat sources in the deepest, darkest parts of your house, then be sure to check on them regularly (at least twice a day) and to move them to a sunny or bright location after they have germinated or use artificial light sources such as grow lights.

Seeds Need Humidity To Germinate

Seeds need to raise their moisture content from near-dry to 25 to 50% to germinate which means that they require a source of water. Germination will be fastest, if seeds are placed in a high humidity environment (95% relative humidity) so that soil moisture levels are adequately maintained.

The simplest way of stopping the soil drying out is to wrap the seed container in cling film or storing it in a zip-lock bag or placing a propagation lid or humidity dome over the tray to trap the moisture and create a high humidity environment around the soil and keep the seed moist.

Of course, if the soil is saturated this will prevent that water from clearing and the seed obtaining the necessary oxygen so you should first take action to remove the excess water before raising the humidity levels.

Do Seeds Germinate Faster In The Light or The Dark?

It depends on the seed.

Many seeds will germinate in either light or dark conditions, in which case germinating in darkness tends to be faster as light can slow germination by drying the seed and enabling chemical reactions that removes oxygen. However some seeds require light exposure or complete darkness to germinate.

Plants have evolved to produce seed with the best chance of growing into healthy plants for their climate. Seeds such as lettuce have developed regions in their seed coat which are light sensitive and allows them to respond to their orientation – only germinating if the seed is optimally placed.

Light can travel through soil – but only so far! If a seed that requires light exposure is covered by too thick a layer of soil then germination will not take place. This is why some seeds require only a thin layer of soil or vermiculite after sowing or simply firming into the soil surface.

However seeds such as calendula, germinate less well under light. Generally speaking, larger seeds such as sunflowers and nasturtiums, and most vegetable seeds will germinate better in darkness, with celery and salad seeds like lettuce and rocket being the main exceptions.

For the fastest germination, it’s important to determine the light requirements of your seed before sowing and, if the seed can germinate in darkness, leave it to germinate in a dark warm spot like an airing cupboard and, if it needs light, let it germinate on a sunny windowsill above a radiator.

How To Speed Up Germination When Direct Sowing

If you’re direct sowing seeds into the ground then it’s a different story. We lose much of the environmental controls we get indoors and, beyond ensuring that the soil doesn’t dry out (which usually isn’t an issue in late winter and early spring) we have to turn to the following methods:

One thing we can do to help our seeds germinate faster is to pre-warm the soil. That means relying on the sun to heat the ground by laying black fabric over the growing area through the winter (which will conveniently remove many weeds) or at least a few weeks before sowing.

These fabrics or sheets tend to limit water absorption too which means that the ground will be drier and, hopefully, have a higher air content and therefore stay warmer during the nights.

Alternatively you can try and use horticultural fleece to retain soil temperature overnight. However, it does allow moisture to enter and while it should prevent the temperature from dropping off overnight, it may also limit how hot the soil gets.

The other thing you could try is to use cloches directly over the area where you have sown your seed. While these are normally used to protect plants from frosts, they should also act as mini-greenhouses – warming the soil during the day and keeping the air and a small patch of ground warm overnight.

Use The Right Seed Starting Mix

By sowing seeds in the ideal seed starting mix, you can get fast germination due to the moisture retention and very quickly improve germination rates toomake. A specifically formulated seed starting compost, coconut coir or a blend of the two are great choices for maximising germination rates.

Using additives such as perlite to enhance drainage can also help to create a moist environment without inviting seed or root rot and the lower nutrient concentration will not stunt the growth of a newly emerged seedling.

I create my own mix using the above ingredients and find outstanding germination results, more or less getting germination every time. You can read more about the mix I use and how to make it at home in the article below.

Happy Gardening!