Soaking seeds before planting can help to speed up the germination process.
The soaking approach promotes softening of the seed coat, and thus allows moisture to penetrate more easily.
The most common way of soaking seeds is to submerge them in room temperature water for several hours (or overnight).
Soaking can also be done in vinegar or in the fridge if cold stratification is also required to soften a seed coat and break a seed's dormancy.
For many seeds, a soak of 8-12 hours (easy to do it overnight) in room temperature water is sufficient to soften a seed coat.
Though, like most things in gardening, not everything behaves in the same way. Some seeds, especially trees and shrubs, will also require scarification.
To facilitate this, simply nick or lightly scratch the seed coat; this will allow water to penetrate more easily. Other seeds may require a cold weather stratification to break their dormancy.
Seeds to Soak: Boosting Your Germination Success
Here are some of the many plants that will benefit from a period of soaking before sowing.
Soaking Vegetable Seeds
Beans: (all types, including lima beans, broad beans, and runner beans): benefit from soaking for 8 to 12 hours.
Peas: Soak for 12 to 24 hours in cool water.
Corn/Maize: Soak for 12 hours in water to promote faster and more uniform germination
Okra: These will require a 12 to 24 hour soak in water, or briefly soak in vinegar to help break down their hard seed coats.
Beets: soak for 12 to 24 hours in cool water
Swiss chard: 12 to 24 hours in cool water
Parsley: Your Parsley seeds should be soaked in warm water for 24 hours. This will greatly improve parsley germination rates.
Cilantro/Coriander: soak for 12 to 24 hours in cool water.
Spinach: Soak your Spinach seeds for 12 to 24 hours in cool water to aid germination.
Soaking Flower Seeds
Lupine: Seeds can be either soaked overnight in cool water or scarified with sandpaper. This will help to break the Lupines hard seed coats, and greatly improve germination success.
Sunflower: 12-hour soak in room temperature water.
Nasturtium: Soak Nasturtium seeds for about 10 to 12 hours in room temperature water.
Morning Glory: Soak overnight in water or briefly scarify with sandpaper.
Sweet peas: Soak for 12 to 24 hours in cool water, a brief scarification in the fridge may also help to boost germination success rates.
Delphinium: The seeds of Delphinium seeds should be soaked for 24 hours in cool water.
Poppy: 12 to 24 hours in cool water.
Columbine (Aquilegia): Columbine seed germination will greatly benefit from a period of cold stratification after first being soaked in cool water for a few hours.
Canna: Canna Lily seeds should first be scarified using either sandpaper or a nail clipper, and then soaked for one to two days in warm water.
Baptisia: As these have very hard seed coats, you will first need to use a file or sandpaper to scarify their surface. Follow this up with a 24 hour soak in warm water.
Asclepias: Some Asclepias plant species will require scarification, followed by a 12 to 24 hour soak in cool water. Cold stratification is also recommended as this can help to improve germination rates.
Passionflower: Passiflora plant seeds will benefit from a 12 to 24 hour soak in lukewarm water once they have undergone a brief scarification.
Hibiscus: Scarify seeds with sandpaper or nick them with a knife. Follow this up by soaking Hibiscus seeds for 12 to 24 hours in warm water.
How to Soak Seeds Before Planting
To soak seeds before planting, first place them in a shallow bowl and then cover them with room temperature water. You will get the best results if all seeds are submerged.
For most seeds, you can leave them to soak for about 12 to 24 hours, though some seeds only require a couple of hours, and others a couple of days.
Exceeding the recommended soaking times may be detrimental, as the seeds might begin to rot. Some seeds only need a few hours, so consult specific planting guidelines.
After soaking, drain off the water, and sow immediately into prepared soil or a seeding mixture pot.
What Will Happen If I Don't Soak My Seeds?
Many of these seeds can and will eventually germinate by their own accord if they are not soaked. Though this can take a long time, and the right sowing and environmental conditions will be required.
The soaking process is simply trying to reproduce the wetness that seeds are naturally subjected to over time in their natural environment.
Soaking accelerates the germination process through softening the seed coat, thus making it easier for the embryo to break through the coat.
When a seed has a particularly hard coat, the breaking down of the seed coat can be significantly increased through a combination of soaking, scarifying, and stratification.
Soaking Seeds in Vinegar
Soaking seeds in acidic vinegar is a form of scarification that can be used to help break down very hard seed coats
Some of the more commonly sown seeds that might benefit from a vinegar soak include many members of the Ipomoea, Asclepias, Passiflora, and Hibiscus plant genera.
As vinegar can be very effective at breaking down a seed coat, seeds are usually only soaked in it for about 30 minutes. Perhaps, up to an hour for seeds with particularly hard coats.
Once this time is up, rinse the seeds under clean water to remove any trace of residual vinegar (which may damage the embryo). Sow out the seeds immediately after this rinse, and then treat as normal.
If you have not tried to use vinegar, it is recommended that you don't use it on all your seeds, as they can easily get damaged beyond repair.
Summary
The soaking of plant seeds helps to soften the seed coat. This allows the embryo to break out, and promotes faster and more consistent germination.
