I’m sitting in my garden trying to understand why the cucumbers I planted a month ago are still only seedlings. I guess growing your own vegetables can sometimes be as frustrating as it is rewarding.
So I did a little research I’d like to share with you.
Some really common reasons fruit and vegetables grow slowly (or not at all) are:
- Poor nutrition
- Wrong soil acidity
- Fertilizer burn
- Not enough sunlight/Too much shade
- Too little water
- Too much water/poor drainage
- Too cold
- Too hot
- Pests
- Weeds
- Disease
Let’s talk a little more about each one, and what you can do about them.
1. Poor soil nutrition
Plants need a whole bunch of soil elements to grow properly. Nitrogen, potassium and phosphorus are the big three. But there are a whole lot of others too. And different plants will prefer a different balance.
As plants grow they drain nutrients out of the soil. In the wild, plants and animals grow and die, returning nutrients to the soil in [dramatic voice] the great circle of life.
In the garden, and especially with fruit and veg, we tend to let plants suck all of the nutrients out of a patch of ground and then harvest the most nutritious parts and take them away all together.
So the nutrients are never replaced. And over time, that can lead to soil that’s running low on the basic nutrients new plants need to grow.
What does it look like?
- Slow growth
- Smaller when fully grown
- Delayed flowering or flowering for longer
- Pale or brown leaves
- Fewer or smaller seeds
- Fewer or smaller fruits
There are a whole bunch of soil test kits available to confirm poor soil nutrition like this one available on Amazon.
What can I do about it?
Digging fertilizer into the soil will replenish these vital ingredients.
You will often see fertilizer labelled with three numbers like 10-10-10. That’s the percentage of nitrogen, phosphorus, and potassium compounds in the fertilizer (in that order). So you can choose a fertilizer to match what you need more of in your soil.
2. Soil Acidity
We’ve all seen Hollywood movies showing acid dissolving it’s way through great big chunks of metal (or worse…).
Acidity (or alkalinity) is measured from 1 – 14 on the pH scale. pH 7 is considered neutral. Anything above that is alkaline, and anything below is acidic. Natural garden soil usually sits somewhere between pH 5 and 9.
And there’s actually quite a delicate balance to keep.
The reason is that phosphorus (an important nutrient) only becomes soluble between about pH 6.5 and 7. Which means it can dissolve in water and be taken up by the roots.
But as the soil becomes even more acidic, toxic compounds like those containing aluminium or manganese start to dissolve more easily in water where they can get into plants and start to poison them.
What does it look like?
Below about pH 5.6 manganese becomes soluble. Manganese is a nutrient in small amounts, but toxic at high concentrations. It can make leaves curl up or crinkle.
Below about pH 5, aluminium begins to be soluble. Aluminium toxicity mostly affects roots and can make them grow thicker, branch less and turn brown. The plant may stop growing or even wilt.
A good soil test kit will include a pH test so you can confirm any suspicions.
What can I do about it?
Digging in garden lime, or bone meal over time will make soil less acidic. You may have to repeat this regularly to keep the pH under control.
Using nitrate based fertilizers will tend to make soil less acidic while ammonium based fertilizers tend to make soil less alkaline.
3. Fertilizer Burn
Fertilizer burn is caused by over fertilizing, or by direct contact between fertilizer and leaves – especially if the leaves are wet.
It happens because the fertilizer salts pull moisture out of the plants which causes a chemical burn.
What does it look like?
Look out for these signs anywhere from a few days to a few weeks after adding fertilizer.
- Yellow or brown patches on leaves.
- Wilting
- Slow growth
What can I do about it?
If caught early enough, fertilizer burn can be treated by flushing the soil with water to wash out excess fertilizer. But be aware of where the runoff is going. You can easily wash water contaminated with high concentrations of fertilizer onto other areas of the lawn or garden and spread the problem even further.
4. Not enough sunlight
Plants get their energy from sunlight. And some need as much as 8-10 hours a day. And if they don’t get enough, they won’t be able to grow properly.
What does it look like?
Well…a bit darker than it should do…
We’re really just talking about too much shade.
But you might also see
- Slower growth
- Smaller fruits
- Pale leaves.
- Wiry growth
In extreme cases leaves will begin to lose their green color altogether and the entire plant might even die.
What can I do about it?
You can usually find out how much light a given plant needs with a quick google.
All you can really do is remove any nearby objects casting shade, or move the suffering plant to a sunnier patch of garden.
Of course, too much sunlight could be a problem too. But it’s more likely to kill plants outright than make them grow slowly.
Consider making a Sun Map so you can be sure you are planting in the right spot.
5. Too little water
Plants need water to move sugars and other nutrients around in their veins. And the fruit and vegetables we love the most are big and juicy. Which means growing them takes a lot of water.
Without enough water, the plant won’t be able to get important nutrients to the places they are needed. So it will grow slowly, or not at all.
What does it look like?
Especially during dry spells, keep an eye out for:
- Wilting
- Yellow, brown, brittle or falling leaves
- Fruit ripening or dropping early (and small)
- Stunted growth
The ground my also be dry or cracked. But note that most plants prefer to have one thorough water every so often rather than a small amount every day.
So it is perfectly possible to find happy, healthy plants in dry soil. Or even dehydrated plants in soil that feels damp to the touch (on the surface).
It’s best to use some common sense and keep mental note of watering times (whether by hand or by rain).
What can I do about it?
Different plants need different amounts of water, but a quick google search should help you figure out what you should be aiming for.
Then it’s just a case of watering the right amount, and with the right frequency, to fill in any gaps that the weather doesn’t water for you.
If you can already see signs of dehydration then give a long, deep water straight away. Deep watering encourages roots to grow deep, and even watering at midday or in the evening is better than making an already dehydrated plant wait until the next morning.
Bear in mind, especially in hot, dry weather, water will evaporate faster than usual and maybe before the plant has taken as much as it needs – so you might need to give a little more to compensate.
6. Too much water
Too much water can damage soil structure and cause water logging. And if that goes on for more than a few days it can be very bad for plants, especially the more delicate fruits and vegetables. We’ve talked before about why plants die in waterlogged soil.
The short story is, roots don’t get the oxygen they need, struggle to take up nutrients properly, and struggle to properly move water around the plant.
The result is something that looks pretty similar to not having enough water!
What does it look like?
Just like dehydration, expect to see:
- Wilting
- Yellow, brown, brittle or falling leaves
- Fruit ripening or dropping early (and small)
- Stunted growth
But also look out for:
- Mold or algae around the base of the plant
- Soil that feels wet or mushy when squeezed up into a ball.
What can I do about it?
Usually, too much water will be because of too much rain. And short of moving house, you probably can’t do much about that.
But some things you can work on are:
- Improve drainage
- Increase or redirect runoff
- Check for and treat any root rot
- Move plants to a drier area of garden
We talked about some ways you could achieve that in our detailed write-up here.
7. Too cold
Plants are made up of a lot of water. When temperatures dip below freezing, the water turns to ice and expands, causing cells to burst in a way that’s similar to a severe burn.
Fragile fruit and vegetable plants are especially at risk of being killed of entirely by an unexpected frost – depending on where you live of course.
But freezing isn’t the only way low temperatures can play havoc with growing plants.
Most plants are very seasonal. New seedlings will germinate at a certain time of year. Plants will flower at a certain time of year. And then fruit at another time of year.
The reason they are so good at telling the time (of year) is that they are specially adapted to pick up on small temperature changes between seasons.
So if they are planted in the wrong climate where it is colder than they are used to, they may never get warm enough to realize spring has arrived at all.
What does it look like?
Frost damage
- Brown or Black leaves with dark patches between veins
- Fewer or no fruits
- Plant appears to collapse
Climate too cold, but no frost
- Plants grow slowly or seeds don’t germinate at all
- Delayed flowering or fruiting
What can I do about it?
Frost damage is unfortunately a lot easier to prevent than cure. Some fruit and vegetable plants will recover if you prune back any damaged stems to a healthy sideshoot. Less hardy plants can be grown in warmer patches of garden, or moved into a greenhouse or coldframe over winter.
If you tend to get frost against a fence, hedge or wall then think about how you can rearrange things to improve airflow and allow trapped cold air to drain away.
Planting against a south facing wall (in the northern hemisphere) can give plants that little bit more protection from frost or icy winds.
And of course you need to make sure you are choosing the right plants for whatever climate you have in your garden. The US Department of Agriculture labels climate zones in the US from 0 to 12. You can see which zone you are in here.
8. Too hot
Hot weather causes water to evaporate faster from the large surface area of the leaves. So it maybe isn’t surprising that some of the symptoms of heat stress looks a lot like dehydration.
But while you will obviously need to water more in hot weather, overheating can happen without the plant actually being dehydrated.
Most plants will actively try to reduce the rate they are losing moisture in hot weather. Most evaporation happens from the leaves, so many plants will curl up or drop leaves.
What does it look like?
Wilting, curling or dropping leaves are the classic signs. But there are a lot of other possible reactions, and different plants can react very differently to heat stress.
Some may drop flowers, or not flower at all (tomatoes).
Some may bolt – sending up a flower stalk and prematurely going to see (cool season veg like lettuce).
What can I do about it?
- Choose varieties that suit your climate. The USDA hardiness map comes in handy again here.
- Water more often. But not too often. You can still over water plants in hot weather.
- Water deeper. Long, deep watering will encourage roots to grow deeper into the soil where moisture will hang around for longer.
- Water in the morning. We mentioned it already, but there’s an old myth that watering in the midday sun can cause plants to get scorched when water focuses sunlight on the leaves like a magnifying glass. That probably won’t happen. But water will still evaporate faster at midday. And evening watering leaves plants damp for longer which can encourage fungal infections.
- Make a Sun map. It’s a great way to figure out where the cooler, shadier spots are so you can plan out where to put cooler season plants.
9. Pests
Pests come in all different shapes and sizes. Depending on where you live, you may see anything from beetles, caterpillars and snails to birds, rabbits or even deer.
Most of the time pest damage is pretty obvious. You’ll see chewed up leaves and great big holes in fruits. And with most large pests like birds, deer or rabbits, you will need a physical barrier to keep them away (like a fence or netting).
But some pests can be much more subtle. Especially tiny creepy crawlies that drink sap or damage roots. And then it might seem like your veggies have given up on growing even with very little visible signs of any damage.
But even these tiny sneaky pests leave a few telltale signs behind that you can watch out for.
Sap drinkers
Sap drinking pests can leave leaves shriveled, wilted or yellowing, and are especially damaging to young leaves. While feeding, sap drinkers like aphids squirt out a sticky, sugary liquid called honeydew onto leaves and stems. And it’s common for a black, sooty mold to feed and grow on top of the honeydew.
So keep an eye out for leaves and stems that feel sticky to the touch, and look like they have a black sooty covering (like someone’s tipped ash over them).
If you’re suspicious, take a look at the underside of a couple of leaves. Aphids, whitefly and other common sap drinking pests like to live there in groups.
Aphids can be fired off of stronger plants with a well aimed spray of water, but that might not be a good idea with young or more delicate plants. Slightly soapy water can act as an insecticide, and neem oil is an effective repellent.
Root eaters
Underground root eating grubs like beetle larvae can also do a lot of damage, and for obvious reasons they can be very difficult to detect.
As with other types of root damage, look out for:
- Wilting
- Yellow, brown, brittle or falling leaves
- Fruit ripening or dropping early (and small)
- Stunted growth
But also keep an eye out for adult beetles above ground, or animals like racoons or skunks digging for the grubs.
Root eating grubs can be treated with Heterorhabditis bacteriophora. It’s a bit of a mouthful – but Heterorhabditis bacteriophora are parasitic nematodes that feed and multiply inside root eating beetle larvae. They can be bought from a garden center or online as a biological pesticide.
10. Weeds
Vegetables may look peaceful. But under the surface there’s a war going on!
Well okay, that might be overdoing it a little. But the fact is, each square foot of soil only contains a finite amount of important resources like water, nutrients and sunlight.
Some plants are very good at growing quickly and grabbing up as much of those resources as they can.
And when that happens, there’s not much left for anything else growing nearby.
The plants we usually call weeds are just the ones that have adapted to be the most effective at growing quickly, securing resources, and strangling out the competition.
But it’s important to realize, any two plants we put too close together are going to have a negative effect on each other. Even if we actually wanted both of them. So accidental overcrowding is actually exactly the same problem.
What does it look like?
If a plant is being crowded out, then it means one of two things. Either the roots aren’t getting enough nutrients or water, or the leaves aren’t getting enough sunlight. So look for signs of general root damage or lack of sunlight.
- Wilting
- Pale, Yellow, brown, brittle or falling leaves
- Fruit ripening or dropping early (and small)
- Stunted growth
- Wiry growth
What can I do about it?
Unfortunately, curing a weed problem is mostly going to come down to carefully digging them out by hand.
With a lot of weeds it’s important to make sure you get the root out in one piece. Bindweed for example can regrow a whole new plant from a piece of root only two inches long left underground.
So weed early, weed often, and try to get them out while they are still seedlings.
11. Disease
Just like humans, plants are commonly infected by viruses, bacteria, or fungi. Diseases directly damage plant cells as well as sapping vital nutrients to grow themselves.
What does it look like?
There are as many different plant diseases as there are human diseases. But an awful lot of them show up as ugly, irregularly shaped dark, brown or rust-colored lesions on leaves or fruits.
What can I do about it?
Half of the battle is prevention. And many common vegetable diseases can be prevented by making sure there is good air circulation (by pruning out excess stems and foliage), and making sure leaves, fruits and roots are not staying damp for long periods of time (by watering correctly and in the morning rather than evening).
But even with care, there are plenty of vegetable diseases that are unavoidable.
If you’re already at the point where you’re seeing lesions or rust colored speckles on leaves or fruit, then it’s important to quickly understand exactly what disease you are dealing with so it can be properly treated.
If that’s you, then this gallery of common vegetables diseases from the university of Maryland might help with diagnosis.
