April gardening tips: How to plant 'old' seeds, rehydrate soil that repels water

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Containers display blooming flowers. Photo courtesy Getty Images.

by UC Master Gardeners of Santa Clara County

Do you have a gardening question? The UC Master Gardeners of Santa Clara County can help. Our volunteers are part of the University of California’s Cooperative Extension program and we are trained to use research-based information to educate our fellow residents on sustainable gardening and landscaping practices specifically for our area.

Our monthly “Ask a Master Gardener” column will answer your questions and offer tips. Have a question? Email lifestyle@embarcaderopublishing.com or leave a comment at the end of this month’s column.

When I water some of my potted plants, the water comes through the holes but the plant still seems wilted. What could be the problem?

This sounds like a classic case of hydrophobic soil. Many potting soils become hydrophobic – meaning they tend to repel water – when they dry out and become difficult to rewet. The term is hydrophobic – not to be confused with the term hydroponic!

We’ve had this question before, so the Santa Clara Master Gardeners published this article on how to water hydrophobic soil, along with a how-to video:

Gardeners may see water draining out the bottom of a pot and assume that means that the soil is saturated. But the water might be running between the side of the pot and the hydrophobic root ball instead, barely wetting the outer surface and leaving the center of the root ball dead dry. Small seedlings from nurseries are particularly prone to this, especially if they have become rootbound. It can happen to large container plants as well.

Potting soils often contain peat moss, which is valued because it decomposes slowly, is lightweight and retains water. Paradoxically though, when peat moss dries out, it is very difficult to rewet. Bags of potting soil can even dry out in storage.

Simply watering hydrophobic soil as usual is unlikely to rehydrate the soil since it resists rewetting.

Here are effective techniques for rehydrating a pot of hydrophobic soil:

Submerge the whole pot in a bucket of water. This is drastic but fast. Initially, there will be so much air in the root ball that the pot will float. When holding it under water, you will see the air bubbles escaping as the air is displaced by water. Remove the pot once the bubbling stops.
Set the pot in a shallow container of water (if size allows), allowing the soil to slowly absorb the water. This technique is known as bottom watering. It may take an hour or more to thoroughly rewet the soil. Be careful not to leave pots soaking in standing water continuously. Check them after an hour or two and remove them when they are hydrated.
For large containers that can’t be lifted easily, you will need to trickle water onto the soil slowly enough so that the water has time to absorb instead of running off. If using a hose on a very slow trickle, be sure to set a timer so you don’t forget about it.
If rain is forecast, you can let the rain do the work for you.
Notice that just as a full glass of water weighs more than an empty glass, a well-watered pot will be heavier than a dried-out one. Get to know how heavy a well-watered pot should feel.

We also see the same hydrophobic soil problem with plants that are transplanted right into the ground. It’s discouraging to dig up a dead plant and find that root ball is still in the shape of the original container. A solution is to briefly soak the root ball until it’s thoroughly hydrated before planting.

Can you plant ‘old’ seeds?

Seed packets have a “packed for” date on the back. Yet seeds can still be viable for years beyond that date if stored correctly. Ideal storage conditions are cool and dry. The older the seeds are, the lower the germination rate will be, so plant more of the older seeds than the number of plants you ultimately want. You can do a germination test by putting seeds on a damp paper towel and enclosing them in plastic to keep them uniformly moist. Do this right before planting time, so you can transplant the ones that successfully germinate. Or you can take your chances and just plant them directly, and see what comes up. If you are saving your own seeds, make sure to choose seeds from the healthiest plants.

If you have some old flower seed packets, you can scatter the seeds randomly in a section of your yard and enjoy whatever blooms. More Information: Vegetable Seed Viability

What are some alternatives to lawn?

If you’re looking for something that doesn’t need regular mowing, something that uses less water or you’re not ready to completely remove your lawn, walkable alternatives include California native options of red fescue and meadow sedge, as well as other alternatives such as white clover, UC Verde buffalograss, Kurapia, Dymondia and thyme. More information: Lawn & Lawn Alternatives