Once they do, they compete with crops for moisture, nutrients, light, and space, and in many cases they out-compete them. That's why the most successful vegetable farmers make weed control a priority. They prevent weeds from getting established, and they don't let weeds growing near their fields go to seed. Over time, the weed seed bank diminishes, and weeding becomes less of a major chore.
On a new farm or in a new field, however, you can expect that weeding is going to be a big part of your workload. You'll probably have to deal with both annual and perennial weeds, so you'll need different strategies and tools. Here are some suggestions for staying ahead of weeds.
Generally speaking, annual weeds come from seeds that either dropped on the surface of the soil or were brought up to the surface by plowing, tilling, or other soil disturbance. All weed control efforts, therefore, should aim to disturb the soil as little as possible to avoid giving new seeds conditions favorable for germination.
The first line of defense against annual weeds is cultivation. The ideal time to cultivate is when weeds are in what's known as the "thread stage," which means they have just germinated and are no thicker than a thread. At that point, they are easily removed with a quick pass of a wheel hoe, or by a small, lightweight tool such as a collinear hoe. As weeds get bigger, cultivation tools need to get bigger and stronger to deal with them. Johnny's trapezoid hoes and stirrup hoes are available in several sizes to deal with increasingly tough weed problems. Read the product descriptions carefully when buying tools to ensure that you have a hoe for each type of weed situation.
A popular weed-control strategy on organic vegetable farms is called "stale seedbed" planting, in which a bed is tilled and irrigated to encourage weed seeds to germinate. The weeds are killed before the crop is planted or right before the crop emerges. Weeds are best killed by flame weeding with a propane torch, which won't disturb the soil and bring up new weed seeds. Here is an example of how to do stale seedbed planting: Till a bed, direct seed a crop such as carrots, and irrigate the bed. A few days before the crop is expected to emerge, flame weed or very shallowly hoe the entire bed. When the crop emerges later, it won't have to compete with weeds right away and can get off to a good start. You can tell when a crop is going to emerge by digging up a few seeds to see whether they are starting to germinate. Or you can place a piece of glass over a small part of the row; the glass will warm the soil and get the seeds below it to germinate a few days ahead of the rest.
Another approach to weed control is to cover bare soil with mulch. The key to success with plastic and biodegradable film mulch is to get it on while the soil is free of weeds, and to stretch it taut for maximum soil contact. Keep planting holes as small as possible, just big enough to accommodate the mature size of the crop but with no extra space where weeds can grow. Some growers use landscape fabric, which can last a decade or more if handled well, for paths and even on beds. The heavy black fabric is best for long-season crops such as tomatoes. Organic mulches such as hay and straw are more difficult and time-consuming to apply, but they benefit the soil by adding nutrients and organic matter as they decompose.
Another important strategy for getting ahead of annual weeds is to keep the soil covered with cover crops whenever possible. If there is a short window between harvest and planting, say a month or two between spring and fall crops, a quick annual such as buckwheat can be planted to keep the soil covered so weeds can't get established. Cover crops also can be used for a longer period, or even a full season, to combat a weed problem. The key is to choose the right cover crop that will germinate and grow quickly, outcompeting weeds.
Johnny's cover crop chart summarizes the best uses for many cover crops. Some other good resources are "Plant and Manage Cover Crops for Maximum Weed Control" from the Virginia Association for Biological Farming and the book, "Managing Cover Crops Profitably" by the Sustainable Agriculture Network, available in the JohnnySeeds.com bookstore.
A much bigger problem, especially for organic growers, are the perennial weeds such as bindweed, Canada thistle, yellow nutsedge, pokeweed, and dock. Not only do they survive year to year, they also are able to re-grow quickly after cultivation from vegetative parts such as roots and tubers. In many cases, cultivation (cutting off the parts above the soil) stimulates the below-ground parts to send up even more stems and can spread pieces of root to new areas. In addition, many perennial weeds are prolific seed producers, so they are able to propagate themselves in multiple ways throughout the season.
If perennial weeds are sparse, you may be able to dig each one with a shovel; just try to get the entire root system. If the roots cannot be removed, keep cutting or mowing the plant to reduce its energy stores below ground, and never let it go to seed.
If perennial weeds are prolific, you may need a summer fallow period in which no crops are planted. Instead, plow the field to bring up the roots of big weeds and let them die on the surface. The perennials will re-sprout, but they will be weakened. Cultivating repeatedly will kill or diminish most of the weeds. A summer fallow may be needed every two or three years in rotation with vegetable crops if weed problems are severe.
Scouting for pests and diseases
One of the fringe benefits of weeding is that while you are out there hoeing or hand pulling weeds, you can monitor crops for any signs of damage from pests or diseases. Turn over leaves and look at the undersides, as that is where many insects lay eggs and where diseases first appear. If a plant is wilted, pull it up and look at the roots to see if they are stunted or rotting. Unless you are familiar with a specific insect and know that it's going to harm your crop, do some research before you take action.
Many insects are beneficial and you should learn what they look like in all their life stages so you don't inadvertently kill these allies. Likewise, learn the life cycles of pests that are common in your area so you can watch for them even before they start to do damage. We highly recommend the book Garden Insects of North America by Whitney Cranshaw. This is a huge (656 pages), comprehensive book about insects that are likely to be found in vegetable and fruit fields and gardens. Insects are categorized by the type of damage they do, which makes it easy to narrow down the potential culprits when you spot a problem.
Another essential reference is Identifying Diseases of Vegetables from Penn State University, which includes concise descriptions and large color photos of common diseases.
In addition, there are many online resources to help you identify problems. Check with your State Extension Service to see if it has an IPM (Integrated Pest Management) program for vegetables and fruits. If so, you might find information that will be targeted to your area. If not, do an internet search for "IPM vegetable" and pick the site from the state nearest yours. Many of these IPM sites have excellent photos.
Once you know the nature of the problem you're dealing with, you can turn to Johnny's chart of physical, biological, and botanical controls for all the most common pests and diseases of vegetables.
The chart lists multiple strategies, from row cover to inexpensive repellents to certified-organic insecticides.
Keep records of pest and disease outbreaks. Write down the dates you noticed the problem and took action on it; the plant's stage of development; the temperature and general weather conditions. Review your notes at the start of next season, and you'll be better prepared to catch problems before they become serious.
First, please note that this information applies only to indeterminate tomato varieties. Determinates should NOT be pruned because pruning will reduce yield.
Indeterminates, however, will grow until killed by frost, always dividing their energy between vegetative growth and fruit production. Appropriate pruning reduces vegetative growth to the minimum required for plant health, thereby increasing the energy available for flowering and fruiting. Pruned tomatoes produce larger fruits that ripen earlier, sometimes by as much as two weeks. Pruning also helps prevent foliar diseases because it reduces crowding and touching of leaves. Too much pruning, however, can result in fruits with sunburn, catfacing, and blossom end rot.
Indeterminate tomatoes are vining plants with many branches. Pruning reduces the number of branches to one, two, or several main branches or "leaders" which will ideally be about the same size. This is accomplished by removing side shoots or "suckers" that grow in the leaf axils between leaves and the stem. Here's how it's done:
1. If you want just one leader, remove all the leaves and side shoots below the first flower cluster. As the plant grows, continue to remove all suckers from the leaf axils.
2. If you want two leaders, which is often recommended in case the main stem is damaged, leave one sucker directly below the first flower cluster. Prune all other suckers that grow on both stems.
3. For plants with three or four leaders, leave the first sucker or first two suckers above the first flower cluster. After that, prune off all new suckers.
The suckers should be removed when they are 2-3" long. In most cases, they will snap off when bent, although if the plant is wilted they may need to be pruned off with pruners or a razor blade. Pruning should be done about every week to 10 days to stay ahead of sucker development. If this task gets away from you and suckers get too long, you should pinch or cut off the growing tip of the sucker, leaving a few leaves behind, rather than trying to remove the entire shoot, which would create a wound close to the main stem and make it more vulnerable to disease.
For more information, see Johnny's video "How to Prune Tomatoes."
Training systemsOpinions vary about the best way to prune and train indeterminate tomatoes, with four primary strategies used by commercial growers:
Sprawl or ground culture involves neither pruning nor staking. Plants are left growing on the ground or on plastic mulch.
Cage systems involve pruning the plants to three or four leaders and confining them inside a cage.
Stake and Weave or basket weave requires plants to be pruned to one or two vines, and supported by twine strung between stakes beside every other tomato plant.
Trellis systems require plants to be pruned to two leaders that are tied to twine hanging from a wire stretched overhead.
Each system has advantages and disadvantages. Oklahoma State researchers compared the four systems and found that trellis culture, with the plants pruned to two leaders, resulted in the earliest and largest tomatoes and the best pest control. However, fruit cracking and sunburn were problems. Cage production resulted in the largest marketable yield, but ranked lower in earliness, fruit size, fruit cracking and rotting, and pest control. Ground culture was the worst in almost all measures. The system that seemed the best balance between yield and quality was Stake and Weave.
For more information, see "Training Systems and Pruning in Organic Tomato Production" by Oregon Tilth.
For information, read article on training hoophouse tomatoes in the Catalog Extras section of JohnnySeeds.com